Basic immunology

Basic immunology
BASIC IMMUNOLOGY BY MOHAMMAD AKHEEL II YEAR PG OMFS
BASIC IMMUNOLOGY IMMUNITY ANTIGENS ANTIBODIES - IMMUNOGLOBULINS ANTIGEN – ANTIBODY REACTIONS COMPLEMENT SYSTEM STRUCTURE AND FUNCTION OF IMMUNE SYSTEM IMMUNE RESPONSE HYPERSENSITIVITY AUTOIMMUNITY ORAL IMMUNOLOGY
IMMUNITY The term Immunity is derived from the Latin word Immunitae, which referred to the protection from the legal prosecution offered to Roman Senators during their tenure in office. Refers to the resistance exhibited by the host towards injury caused by microorganisms and their products. Protection against infectious diseases Distinguishes self from non-self Eliminate potentially destructive foreign substances from body
IMMUNITY INNATE ACQUIRED Non specific Specific Active Passive Species Racial Artificial Individual Natural
INNATE IMMUNITY ACQUIRED IMMUNITY Resistance to infection which individual The resistance that an individual possesses by virtue of his genetic and acquires during life constitutional make up Early defense response against Later defense response microbes Immune response Non specific Immune response is highly specific Innate response do not alter on repeated Adaptive response improves with each exposure successive encounter with same pathogen Memory effect absent Memory effect present Not affected by immunisation or prior Is improved by immunisation contact
INNATE IMMUNITY It consists of cellular and biochemical defense mechanisms that are in place even before infections and poised to respond rapidly to infections. These mechanisms react only to microbes and not to non-infectious substances Innate Immunity Species Racial Individual
Species immunity  Refers to the total or relative refractoriness to a pathogen, shown by all members of species.  Person obtains by virtue of being a part of the human species.  Determines whether or not a pathogen can multiply in them. For e.g.  All human beings are totally unsusceptible to plant pathogens and to, many animal pathogens, such as render pest or distemper. Pasteur’s experiments on anthrax in frogs, which are naturally resistant to the disease but become susceptible when their body temperature is raised from 25° to 35°C.
Racial immunity  Racial differences are known to be genetic in origin For e.g.  People of Negroid origin in USA are more susceptible than the Caucasians to tuberculosis.  Genetic resistance to Plasmodium falciparum Malaria seen in some parts of Africa and Mediterranean coast. A hereditary abnormality of red cells (sickling) prevalent in the area, confer immunity to infections by malarial parasite.
Individual immunity  The difference in innate immunity exhibited by different individuals in a race  The genetic basis of individual immunity is seen in twins. For e.g. Homozygous twins exhibit similar degrees of resistance or susceptibility to Lepromatous leprosy and Tuberculosis.
Innate immunity does not recognize every possible antigen instead it recognizes pathogen-associated molecular patterns. Receptors enable the phagocyte to attach to these patterns so it can be engulfed and destroyed by lysosomes. Pathogen-Associated Molecular Patterns Binding to Endocytic Pattern- Recognition Receptors on Phagocytes
Determinants of innate immunity I. Species and strains II. Age III. Hormonal Influences IV. Nutrition
MECHANISMS OF INNATE IMMUNITY I. Epithelial surfaces Skin Mucosa of the respiratory tract Human eye. Flushing action of urine II. Antibacterial substances in Blood and tissues III. Inflammation IV. Fever V. Cellular factors
ACQUIRED IMMUNITY A person is said to be immune when he possesses specific protective antibodies or cellular immunity as a result of previous infection or immunization or is so conditioned by such previous experience as to respond adequately to prevent infection Because this form of immunity develops as a response to infection and is adaptive to the infection, it is called adaptive immunity. The characteristics of adaptive immunity are  Specificity for distinct molecules.  An ability to remember and respond more vigorously to repeated exposure to the same microbe. Hence it is also called as specific immunity.
ACTIVE IMMUNITY PASSIVE IMMUNITY 1. Produced actively by host’s immune Received passively by the host system 2. Induced by infection or by contact No participation by the host’s immune with immunogens (vaccines, system allergens etc). 3. Affords desirable and effective Conferred by introduction of protection readymade antibodies 4. Immunity effective only after a lag Protection transient and less effective period (time required for generation Immunity effective immediately of antibodies). 5. Immunological memory present; No immunological memory subsequent challenge more subsequent administration of effective (booster effect) antibodies less effective due to immune elimination 6. Negative phase may occur No negative phase 7. Not applicable in immunodeficient Applicable in immunodeficient hosts hosts
Natural Active immunity  This results from either a clinical or inapparent infection.  Immunity following chicken pox and measles infection is usually life long Artificial Active Immunity This is the resistance induced by vaccines. Vaccines are preparations of live or killed microorganisms or their products used for immunization.
Types of Vaccine: Immunizing agents that are used for immunoprophylaxis  Bacterial vaccines: Live (BCG vaccine for T.B.). Killed (Cholera vaccine). Subunit (Typhoid Vi antigen). Bacterial products (Tetanus Toxoid).  Viral Vaccine: Live (Oral polio vaccine – Sabin). Killed (Injectable polio vaccine – Salk). Subunit (Hepatitis B-vaccine).  Combinations If more than one kind of immunizing agent is included in the vaccine, it is called a mixed or combined vaccine. DPT (Diphtheria – pertussis - tetanus) MMR (Measles, mumps and rubella). DPTP (DPT plus inactivated polio).
Natural Passive immunity  This is the resistance passively transferred from the mother to the baby. In human infants, maternal antibodies are transmitted predominantly through the placenta.  Human colustrum, which is also rich in IgA antibodies and resistant to intestinal digestion. Synthesis of antibodies (IgM) occurs at 20th week of IUL but its immunogenic capacity is still inadequate at birth. It is only by about the age of three month that the infants acquire a satisfactory level of immunological independence.
Artificial passive immunity This is the resistance passively transferred to a recipient by administration of antibodies. Passive immunization is indicated for immediate and temporary protection in a non-immune host Employed for the suppression of active immunity, when the latter may be injurious. Used as treatment of some infections. Hyper immune sera of animal or human origin, convalescent sera and pooled human gamma globulins are used for prophylaxis and therapy. Rh immune globulin is used during delivery to prevent immune response to the Rhesus factor in Rh-negative women with Rh-positive babies.
Cells of the Innate Immune System: Phagocytes Macrophages play several roles in the immune responses:  Phagocytosis.  Required to process and present antigen to immunocompetent T cells for induction of CMI.  Production of cytokines, such as IL-1 and TNFα, which are proinflammatory  Lyses tumor cells by secreting toxic metabolites and proteolytic enzymes  Examples of tissue macrophages are kuppfer cell of the liver, microglial cells of brain, mesangial phagocyte of the kidney, alveolar macrophages of lungs and osteoclasts of bone.
NEUTROPHILS: Mediate the earliest phase of inflammatory response and aids in phagocytosis. The cytoplasm contains enzymes such as lysozyme, collagenase, elastase lactoferrin, acid hydrolase, and myeloperoxidase and other microbicidal substances. Enzymes stimulates Kallikrein catalyzes Bradykinin promotes Inflammation They also possess receptors for IgG antibody. These receptors enable neutrophils to participate in the inflammatory response and phagocytosis.
EOSINOPHILS They are phagocytic cells. contains receptors for immunoglobulins, growth factors and complement components on the cell surface Their primary function may be secretion and extracellular killing rather than intracellular. perform specialized function namely immediate hypersensitivity in response to parasites and protozoa. secrete destructive enzymes such as acid phosphatase, peroxidases and proteinases and promotes inflammation
Mast cell Has inflammatory mediators such as histamine, eosinophils chemotactic factor, neutrophil chemotactic factor and heparin and zinc ions. It also synthesizes SRS-A, TNFα and leukotriene C4. These cells possess receptors for complement components (C3a and C5a) as well as receptors for the Fc portions of the antibody molecules, IgE and IgG The stimulation of these receptors can result in activation and secretion of vasoactive substances that increase vascular permeability and dilation.
BASOPHILS Basophils contain several enzymes, histidine carboxylase. release histamine, leukotrienes, and prostaglandins, chemicals that promotes inflammation MONOCYTES phagocytes. Monocytes differentiate into macrophages serve as antigen-presenting cells in the adaptive immune responses LYMPHOCYTES B-lymphocytes (B-cells) mediate humoral immunity T-lymphocytes (T-cells) mediate cellular immunity
ANTIGENS An antigen has been defined as any substance which when introduced parenterally into the body stimulates the production of an antibody with which it reacts specifically and in an observable manner The two attributes of antigenicity are:  Induction of an immune response (immunogenicity).  Specific reaction with antibody or sensitized cells (immunological reactivity). Based on the ability of antigens to carry out these two functions, they may be classified into different types:  Complete antigen is able to induce antibody formation and produce a specific and observable reaction with the antibody so produced.  Haptens are substances, which are incapable of inducing antibody formation by themselves, but can react specifically with antibody.
Determinants of Antigenicity: Size: Large molecular size (6.75 million) : highly antigenic Low molecular size (<5000) : less or non-antigenic Chemical nature: Proteins and polysaccharides : highly antigenic. Lipids and nucleic acids : less antigenic. Susceptibility to tissue enzymes: only substances, which are metabolized and are susceptible to the action of tissue enzymes, behave as antigens. Foreignness: Only antigens that are foreign to the individual (non self) induce an immune response. Antigen Specificity: It is the position of the antigenic determinant group in the antigenic molecule at ortho, meta and para positions which determines antigen specificity. It is not absolute. Cross reaction can occur between antigen which bear stereo-chemical similarities
Antigen reacting only with particular Immunocytes B-lymphocytes have sIg molecules on their surface that recognize epitopes directly on antigens. Different B-lymphocytes are programmed to produce different molecules of sIg, each specific for a unique epitope.
Iso specificity: Isoantigens are antigens found in some but not all member of a species. A species may be grouped depending on the presence of different antigens in its members e.g. human erythrocyte antigen based on which individuals can be classified into different blood groups. Autospecificity: Autologous or self-antigens are ordinarily non-antigenic but there are exceptions. Sequestered antigens that are not normally found free in circulation or tissue fluids (such as lens protein normally, confined within its capsule) are not recognized as self-antigens. Similarly antigens that are absent during embryonic life and develop later (such as spleens) are also not recognize as self-antigens.
ANTIBODIES (IMMUNOGLOBULINS) They are specific glycoprotein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen. Antibody Structure A monomer has four glycoprotein chains:  two identical heavy chains have a high molecular weight that varies with the class of antibody.  two identical light chains. The light chains come in two varieties: kappa or lamda and have a lower molecular weight. The four glycoprotein chains are connected to one another by disulfide (S-S) bonds and noncovalent bonds Additional S-S bonds fold the individual glycoprotein chains into a number of distinct globular domains. The area where the top of the "Y" joins the bottom is called the hinge. This area is flexible to enable the antibody to bind to pairs of epitopes at various distances apart on an antigen. The two tips of the "Y" monomer are referred to as the Fab portions of the antibody.
The Fab portion of the antibody has specificity for binding an epitope of an antigen. The Fc portion directs the biological activity of the antibody.
Folding Domains of an Antibody The Fab portion of the antibody has the complementarity-determining regions (red) providing specificity for binding an epitope of an antigen. The Fc portion (purple) directs the biological activity of the antibody. (S-S = disulfide bond; N = amino terminal of glycoprotein; C = carboxy terminal of glycoprotein; CHO = carbohydrate.)
Epitope of an Antigen Binding to Fab of an Antibody
Ways That Antibodies Help to Defend the Body 1. Opsonization: Using antibodies to attach microbes to phagocytes or phagocytes to cells recognized as nonself. 2. MAC Cytolysis: Using antibodies to activate the classical complement pathway resulting in the lysis of gram-negative bacteria and cells recognized as nonself by way of the membrane attack complex (MAC). 3. Antibody-dependent Cellular Cytotoxicity (ADCC) by NK Cells: Using antibodies to attach NK cells to infected cells and tumor cells. 4. Neutralization of Exotoxins: Using antibodies to prevent exotoxins from binding to receptors on host cells.
5. Neutralization of Viruses: Using antibodies to prevent viruses from binding to receptors on host. 6. Preventing Bacterial Adherence to Host Cells: Using antibodies to prevent bacteria from binding to receptors on host. 7. Agglutination of Microorganisms: Using antibodies to clump microbes together for more effective phagocytosis. 8. Immobilization of Bacteria and Protozoans: Using antibodies to against cilia and flagella to block motility.
The 5 Classes (Isotypes) of Human Antibodies a. IgG (Immunoglobulin G; 4 subclasses) IgG makes up approximately 80% of the serum antibodies. The Fc portion of IgG can activate the classical complement pathway. bind to macrophage and neutrophils for enhanced phagocytosis. bind to NK cells for antibody-dependent cytotoxicity (ADCC). enables it to cross the placenta. (IgG is the only class of antibody that can cross the placenta and enter the fetal circulation.)
IgG
A Bacterial Capsule Preventing C3b Receptors on Phagocytes from Binding to C3b Attached to a Bacterial Cell Wall In some bacteria, the capsule covers the opsonin C3b bound to the bacterial cell wall so that it can't bind to C3b receptors (called CR1) on the surface of phagocytes.
Opsonization of an Encapsulated Bacterium The Fab portion of IgG binds to epitopes of a capsule. The Fc portion can now attach the capsule to Fc receptors on phagocytes for enhanced attachment. Once attached to the phagocyte by way of IgG, the encapsulated bacterium can be engulfed more efficiently and placed in a phagosome.
b. IgM (Immunoglobulin M) IgM makes up approximately 13% of the serum antibodies and is the first antibody produced during an immune response. The Fc portions of IgM are able to activate the classical complement pathway. (IgM is the most efficient class of antibody for activating the classical complement pathway.) Monomeric forms of IgM are found on the surface of B-lymphocytes as B- cell receptors or sIg.
IgM IgM is a pentamer and, therefore, has 10 Fab sites.
c. IgA (Immunoglobulin A; 2 subclasses)  IgA makes up approximately 6% of the serum antibodies  IgA is found mainly in body secretions (saliva, mucous, tears, colostrum and milk) as secretory IgA (sIgA) where it protects internal body surfaces exposed to the environment by blocking the attachment of bacteria and viruses to mucous membranes. While only 6% of the antibodies in the serum are IgA  The Fc portion of secretory IgA binds to components of mucous and contributes to the ability of mucous to trap microbes.  IgA can activate the alternative complement pathway.
Secretory IgA Secretory IgA is a dimer and has 4 Fab sites. A secretory component helps protect it from digestion in body secretions.
d. IgD: (Immunoglobulin D; 2 subclasses) IgD makes up approximately 0.2% of the serum antibodies. IgD is found on the surface of B-lymphocytes (along with monomeric IgM) as a B-cell receptor or sIg where it may control of B-lymphocyte activation and suppression. IgD may play a role in eliminating B-lymphocytes generating self- reactive autoantibodies.
e. IgE (Immunoglobulin E) IgE makes up about 0.002% of the serum antibodies Most IgE is tightly bound to basophils and mast cells via its Fc region. The Fc portion of IgE made against parasitic worms and arthropods can bind to eosinophils enabling opsonization. The Fc portion of IgE can bind to mast cells and basophils where it mediates many allergic reactions. Cross linking of cell-bound IgE by antigen triggers the release of vasodilators for an inflammatory response.
ANTIGEN-ANTIBODY REACTIONS Antigens and antibodies, by definition, combine with each other specifically and in an observable manner. In vivo, they form the basis of antibody mediated immunity in infectious diseases, or of tissue injury in some types of hypersensitivity and autoimmune diseases. In vitro In the laboratory, they help in the diagnosis of infections,in epidemiological surveys, in the identification of infectious agents and of noninfectious antigens such as enzymes. In general, these reactions can be used for the detection and quantitation of either antigens or antibodies. Antigen-antibody reactions in vitro are known as serological reactions.
General features of antigen-antibody reactions I. The reaction is specific, an antigen combining only with its homologous antibody and vice versa. 2. Entire molecules react and not fragments. When an antigenic determinant present in a large molecule or on a 'carrier' particle reacts with its antibody, whole molecules or particles are agglutinated. 3. There is no denaturation of the antigen or the antibody during the reaction. 4. The combination occurs at the surface. Therefore, it is the surface antigens that are immunologically relevant.
5. The combination is firm but reversible. The firmness of the union is influenced by the affinity and avidity of the reaction. Affinity refers to the intensity of attraction between the antigen and antibody molecules. It is a function of the closeness of fit between an epitope and the antigen combining region of its antibody. Avidity is the strength of the bond after the formation of the antigen- antibody complexes. 6. Both antigens and antibodies participate in the formation of agglutinates or precipitates. 7. Antigens and antibodies can combine in varyring proportions, unlike chemicals with fixed valencies. Both antigens and antibodies are multivalent.
SEROLOGICAL REACTIONS Precipitation reaction When a soluble antigen combines with its antibody in the presence of electrolytes (NACI) at a suitable temperature and pH, the antigen-antibody complex forms an insoluble precipitate. When, instead of sedimenting, the precipitate remains suspended as floccules, the reaction is known as flocculation. Mechanism of precipitation Marrack (1934) proposed the lattice hypothesis. Multivalent antigens combine with bivalent antibodies in varying proportions. Precipitation results when a large lattice is formed consisting of altemating antigen and antibody molecules. The lattice hypothesis holds good for agglutination also.
Antigens : Dark spheres Antibodies : Spindles Mechanism of Precipitation by lattice formation A: Antigen excess C: Antibody excess (Lattice formation does not occur) B: (Zone of equivalence) Lattice formation and precipitation occur optimally
Applications of precipitation reaction It is very sensitive in the detection of antigens as little as 1 pg of protein can be detected by precipitation tests. Finds forensic application in the identification of blood and seminal stains, and in testing for food adulterants. The following types of precipitation and flocculation tests are in common use: Ring test: Grouping of streptococci by the Lancefield technique. Slide test: The VDRL test for syphilis is an example of slide flocculation. Tube test: The Kahn test for syphilis is an example of a tube flocculation test.
AGGLUTINATION REACTION When a particulate antigen is mixed with its antibody in the presence of electrolytes at a suitable temperature and pH, the particles are clumped or agglutinated. Agglutination is more sensitive than precipitation for the detection of antibodies. The same principles govern agglutination and precipitation. Agglutination occurs optimally when antigens and antibodies react in equivalent proportions.
Applications of agglutination reaction Slide agglutination: When a drop of the appropriate antiserum is added to a smooth, uniform suspension of a particulate antigen in a drop of saline on a slide or tile, agglutination takes place. A positive result is indicated by the clumping together of the particles an the clearing of the drop. It is the method used for blood grouping and cross matching. Tube agglutination: This is a standard quantitative method for the measurement of antibodies. When a fixed volume of a particulate antigen suspension is added to an equal volume of serial dilutions of an antiserum in test tubes, the agglutination titre of the serum can be estimated. Tube agglutination is routinely employed for the serological diagnosis of typhoid, brucellosis and typhus fever.
COMPLEMENT SYSTEM: The term complement refers to a system of factors, which occur in normal serum and are activated characteristically by Antigen antibody interaction and subsequently mediate a number of biologically significant consequences. It is a non-specific serologic reagent in that complement from one species can react with antibody from other species. Complement ordinarily does not bind to free antigen or antibody but only to antibody, which has combined with its antigen. All classes of Immunoglobulins do not fix to complement, only IgM. IgG3, 1 and 2 in that order fix complement on the Fc portion of the Immunoglobulin molecule. But not IgG4, A, D & E Complement is a complex of different fractions called C1 to C9. The fraction of C1 occurs in serum as a calcium ion dependent complex, which on chelation with EDTA yields three proteins subunits called C1q, r, and s. This complex is made up of a total of 11 different proteins.
Assembly of C1 during the Classical Complement Pathway The Fab of IgG or IgM bind to epitopes on an antigen. C1q, C1r, and C1s then assembles on the Fc portion of the antibodies to form C1, the first enzyme of the classical complement pathway. The enzyme C1 is able to cleave C4 into C4a and C4b, as well as C2 into C2a and C2b.
Formation of C3 Convertase during the Classical Complement Pathway The enzyme C1 is able to cleave C4 into C4a and C4b. The C4b binds to adjacent proteins and carbohydrates on the surface of the antigen. C2 then binds to the C4b and C1 cleaves C2 into C2a and C2b. The C4b2a functions as a C3 convertase that can subsequently cleave hundreds of molecules of C3 into C3a and C3b.
Formation of C5 Convertase during the Classical Complement Pathway The C4a2b functions as a C3 convertase that can subsequently cleave hundreds of molecules of C3 into C3a and C3b. Much of the C3b binds to adjacent proteins and carbohydrates on the antigen to participate in opsonization while C3a can stimulate inflammatory responses. Some of the C3b binds to C4b2a to form C4b2a3b, a C5 convertase that can cleave C5 into C5a and C5b.
The Membrane Attack Complex (MAC) Causing Cell Lysis This C5b6789n, or membrane attack complex (MAC), puts pores into lipid bilayer membranes of human cells to which antibodies have bound. This results in cell lysis. MAC can also damage the envelope of enveloped viruses and put pores in the outer membrane and cytoplasmic membrane of gram- negative bacteria causing their lysis.
Benefits of C5a and C3b Most C3b binds to antigens on the microbial surface. Some C3b combines with C2a and C4b to form the third enzyme of the complement pathway that is able to split C5 into C5a and C5b. C5a stimulates mast cells to release histamine for inflammation and diapedesis. It also functions as a chemoattractant for phagocytes. The phagocytes are then able to bind to the C3b attached to the surface of the microorganism allowing for opsonization (enhanced attachment).
COMPLEMENT FIXATION TEST (CFT) Ability of antigen antibody complexes to 'fix' complement is made use of in the complement fixation test (CFT). This is a very versatile and sensitive test, applicable with various types of antigens and antibodies and capable of detecting as little as 0.04 mg of antibody nitrogen and 0.1 mg of antigen. CFT is a complex procedure consisting of two steps and five reagents- Antigen, Antibody, Complement, Sheep erythrocytes and Amboceptor (rabbit antibody to sheep red cells).
Inactivated serum incubated at Wassermann Guinea pig of patient 37deg.C for 1hr. with Antigen Complement ( 2 units ) If complement is Fixed (utilised) not fixed (not utilised) Patient serum has Patient serum has no Syphilitic antibody Syphilitic antibody (Complement is left intact) Sheep RBC coated with Haemolysin Incubated at 37deg.C for 30 min. If no lysis of RBC If lysis of RBC Complement was utilised in I step Complement was not utilised SERUM HAS ANTIBODIES SERUM – NO ANTIBODIES
LECTIN PATHWAY Mediated by mannan-binding lectin (also known as mannan-binding protein or MBP). MBP is a protein that binds to the mannose groups found in many microbial carbohydrates but not usually found in the carbohydrates of humans. The MBP is equivalent to C1q in the classical complement pathway. Activation of the lectin pathway begins when mannan-binding protein (MBP) binds to the mannose groups of microbial carbohydrates.
Activation of the Lectin Pathway Activation of the lectin pathway begins when mannan-binding protein (MBP) binds to the mannose groups of the microbial carbohydrates. Two more lectin pathway proteins called MASP1 and MASP2 (equivalent to C1r and C1s of the classical pathway) now bind to the MBP. This forms an enzyme similar to C1 of the classical complement pathway that is able to cleave C4 and C2 to form C4bC2a, the C3 convertase capable of enzymatically splitting hundreds of molecules of C3 into C3a and C3b.
ALTERNATIVE COMPLEMENT PATHWAY The alternative complement pathway is mediated by C3b, produced either by the classical or lectin pathways or from C3 hydrolysis by water. (Water can hydrolize C3 and form C3i, a molecule that functions in a manner similar to C3b.)
Activation of the Alternative Complement Pathway and Formation of C3 Convertase Activation of the alternative complement pathway begins when C3b (or C3i) binds to the cell wall and other surface components of microbes. Alternative pathway protein Factor B then combines with the cell-bound C3b to form C3bB. Factor D then splits the bound Factor B into Bb and Ba, forming C3bBb. A serum protein called properdin then binds to the Bb to form C3bBbP that functions as a C3 convertase capable of enzymatically splitting hundreds of molecules of C3 into C3a and C3b.
Formation of C5 Convertase during the Alternative Complement Pathway Some of the C3b subsequently binds to some of the C3bBb to form C3bBb3b, a C5 convertase capable of enzymatically splitting hundreds of molecules of C5 into C5a and C5b.
Functions of Complement system include:  Control of inflammatory reactions and chemotaxis.  Clearance of immune complexes.  Cellular activation and antimicrobial defense.  Development of antibody responses  Contributes to pathogenesis of Hereditary angioneurotic edema Nephrotoxic nephritis Paroxysmal nocturnal hemoglobinuria Infectious mononucleosis Autoimmune hemolytic anaemia  Complement mediates immunological membrane damage (cytolysis bacteriolysis).  Participates in pathogenesis of Type II & Type III hypersensitivity reaction.  Antiviral activity.  Promotes phagocytosis and immune adherence.  It also interacts with the coagulation, fibrinolytic and kininogenic systems of blood.
Cytokines Cytokines are mediators that function as up and down regulation of immunogenic, inflammatory and reparative host responses to injury. Soluble mediators called cytokines control many critical interactions among cells of the immune system. They generally act over very short distances, being “autocrine” (acting on the cells that produce them) or “paracrine” (acting on cells close by) Cytokines can be of two types: Lymphokines : produced by lymphocyte. Monokines :produced by monocytes or macrophages. Interleukins, Interferons, Tumour necrosis factor and Growth factors are grouped under Cytokines
Interleukin 1 (IL-1): mediates host inflammatory response to infections promote neutrophil margination and migration into an inflamed site. In low conc., as a mediator of local inflammation. in larger conc., exerts endocrine effects. are endogenous pyrogens (i.e. they induce fever) early hematopoietic progenitor in the bone marrow.
Interleukin 2 (IL-2):  This is a growth factor for antigen stimulated T lymphocytes and is responsible for T cell clonal expansion after antigen recognition and stimulus for antibody synthesis.  Potentiates apoptotic death of antigen activated T cells. Interleukin 3 (IL-3):  Induces growth of all types of hematopoetic cells known as multi colony stimulating factor
Interleukin 4 (IL-4): It is secreted by activated CD4+ T cells of the TH2 subset and by mast cells. IL-4 suppresses the induction and function of TH1 cells Enhances IL-3 mediated mast cell growth Increase macrophage expression of class II MHC proteins Interleukin 5 (IL-5): stimulate the production of eosinophils enhances the activities of basophil
Interleukin 6 (IL-6): Promotes B-cell differentiation and IgG production Interleukin 7 (I- 7): A growth factor for both B and T cell progenitor and mature T cells as well as macrophages and monocytes Increases macrophage cytotoxic activity and induces cytokine secretion by monocytes. Interleukin 8 (IL-8): Acts as a neutrophil chemotactic factor
Interferons: In 1957, it was discovered that cells exposed to inactivated viruses produces soluble factor that can “interfere” with viral replication when applied to newly infected cells. The factor was named interferon (IFN). Interferons do not exert their antiviral effects by acting on viral particle but rather by inducing an antiviral state within the host cell that makes it inhospitable to viral replication. This as well as the antiproliferative and immunomodulatory effects of interferon reflects their ability to regulate specific gene expression in their target cells. They can be classified into three distinct types:  INF-α (leukocyte interferon) – type I  INF-β (fibroblast interferon) – type I  IFN-γ (immune interferon) – Type II.
STRUCTURES AND FUNCTIONS OF IMMUNE SYSTEM THE LYMPHOID SYSTEM The body uses the lymphoid system to enable lymphocytes to encounter antigens and it is here that adaptive immune responses are initiated. a. Primary lymphoid organs The bone marrow and the thymus constitute the primary lymphoid organs. B-lymphocytes mature in the bone marrow while T-lymphocytes migrate to the thymus and mature there. b. Lymphatic vessels Lymphatic vessels are responsible for flow of lymph within the lymphoid system and are a part of the body's fluid recirculation system. c. Secondary lymphoid organs Adaptive immune responses require antigen-presenting cells, such as macrophages and dendritic cells, lymph nodes and the spleen
Number of surface antigens or markers have been identified on Lymphocytes. These markers reflect the stage of differentiation and functional properties of cells. When a cluster of monoclonal antibodies was found to react with a particular antigen, it was defined as a separate marker and given a CD (cluster of differentiation) number. CD Cell type association number CD 1 Thymocytes, Langerhans cells CD 2 T cell SRBC receptors CD 3 T cell antigen receptor complex CD 4 Helper T cell (receptor for HIV) CD 8 Suppressor/cytotoxic T cells CD 19 B cells
Antigen-Presenting Cells (APCs) APCs include dendritic cells, macrophages, and B-lymphocytes. 1. Dendritic Cells Captures and present protein antigens to naive T-lymphocytes . (Naive lymphocytes are those that have not yet encountered an antigen.) 2. Macrophages Captures and present protein antigens to effector T-lymphocytes. (Effector lymphocytes are lymphocytes that have encountered an antigen, proliferated, and matured into a form capable of actively carrying out immune defenses.) 3. B-lymphocytes Captures and present protein antigens to effector T4-lymphocytes. triggers the T4-cell to produce and secrete various cytokines that enable that B-lymphocyte to proliferate and differentiate into antibody-secreting plasma cells.
T4-Lymphocytes (T4-Helper Cells, CD4+ Cells) T-lymphocytes displaying CD4 molecules on their surface that regulate the immune responses through their production of cytokines. T4-lymphocytes recognize epitopes bound to MHC-II molecules by way of the T-cell receptors (TCR) and CD4 molecules on their surface. Have a shape, capable of recognizing peptides from exogenous antigens bound to MHC-II molecules on the surface of APCs and B-lymphocytes. The TCR recognizes the peptide while the CD4 molecule recognizes the MHC-II molecule. overall role of these effector T4-lymphocytes is to: 1. activate macrophages and NK cells. 2. produce cytokines that enable activated B-lymphocytes to produce antibodies and T-lymphocytes into effector cells.
Different types of effector T4-lymphocytes based on the cytokines they produce are Th1 cells and Th2 cells. a. Th1 lymphocytes Th1-lymphocytes recognize antigens presented by macrophages and function primarily to activate and heighten cell-mediated immunity by producing cytokines such as interleukin-2 (Il-2), interferon-gamma (IFN-gamma), lymphotoxin, and tumor necrosis factor-beta (TNF-beta). b. Th2 lymphocytes Th2-lymphocytes recognize antigens presented by B-lymphocytes. They produce cytokines such as interleukins 2, 4, 5, 10, and 13 that promote antibody production.
Activation of a Macrophage by a Th1 Lymphocyte 1. Bacteria are engulfed by a macrophage and placed in a phagosome. A lysosome fuses with the phagosome forming a phagolysosome. 2.An activated Th1 lymphocyte binds to a peptide/MHC-II complex on a macrophage by way of its TCR and CD4 molecule. 3.Co-stimulatory molecules such as CD40L on the Th1 cell then bind to CD40 on a macrophage. 4. The Th1 lymphocyte secretes the cytokine interferon-gamma (IFN-gamma) that binds to IFN-gamma receptors on the macrophage. 5. The IFN-gamma activates the macrophage enabling it to produce more hydrolytic lysosomal enzymes, nitric oxide, and toxic oxygen radicals that destroy the microorganisms within the phagosomes and phagolysosomes.
T8 -LYMPHOCYTES T-lymphocytes displaying CD8 molecules on their surface and carrying out cell- mediated immunity. T8-lymphocytes recognize epitopes bound to MHC-I molecules by way of the T-cell receptors (TCR) and CD8 molecules on their surface. During its development, each T8-lymphocyte becomes genetically programmed, by gene-splicing reactions, to produce a TCR with a unique shape capable of binding epitope/MHC-I complex with a corresponding shape One of the body's major defenses against viruses, intracellular bacteria, and cancers is the destruction of infected cells and tumor cells by cytotoxic T- lymphocytes or CTLs.
B-lymphocytes (B-cells) B-lymphocytes refer to lymphocytes that are produced in the bone marrow and require bone marrow stromal cells and their cytokines for maturation. During its development, each B-lymphocyte becomes genetically programmed through a series of gene-splicing reactions to produce an antibody molecule with a unique specificity - a specific 3-dimensional shape capable of binding a specific epitope of an antigen Antibodies on the surface of B-lymphocytes that function as B-cell receptors are also known as surface immunoglobulin (sIg)
a. Activation of naive B-lymphocytes by T-dependent antigens Most proteins are T-dependent antigens. In order for naive B-lymphocytes to proliferate, differentiate and mount an antibody response against T-dependent antigens, these B-lymphocytes must interact with effector T4-lymphocytes. b. Activation of B-lymphocytes by T-independent antigens T-independent (TI) antigens are usually large carbohydrate and lipid molecules with multiple, repeating subunits. B-lymphocytes mount an antibody response to T-independent antigens without the requirement of interaction with T4- lymphocytes.
CLONAL SELECTION: The selection and activation of specific B-lymphocytes and T-lymphocytes by the binding of epitopes to B-cell receptors or T-cell receptors with a corresponding fit. CLONAL EXPANSION: The proliferation of B-lymphocytes and T-lymphocytes activated by clonal selection in order to produce a clone of identical cells. This enables the body to have sufficient numbers of antigen-specific lymphocytes to mount an effective immune response.
Clonal Selection, Step-1 During its development, each B-lymphocyte becomes genetically programmed, through a process called gene translocation, to make a unique B-cell receptor. Molecules of that B-cell receptor are placed on its surface where it can react with epitopes of an antigen.
Clonal Selection, Step-2 B-lymphocyte with an appropriately fitting B-cell receptor can now react with epitopes of an antigen having a corresponding shape. This activates the B- lymphocyte.
An Effector T4-Lymphocyte Recognizing Epitope/MHC-II on an Activated B- Lymphocyte An effector T4-lymphocyte uses its TCR and CD4 molecule to bind to a complementary shaped MHC-II molecule with attached peptide epitope on an activated B-lymphocyte. This interaction, along with the binding of co-stimulatory molecules such as CD40 and B7 on the B-lymphocyte with their complementary ligands on the effector T4-lymphocyte triggers the T4-lymphocyte to produce cytokines that enable the activated B-lymphocyte to proliferate, differentiate into antibody-secreting B-lymphocytes and plasma cells, and switch classes of the antibodies being made.
Proliferation and Differentiation of a B-Lymphocyte after Interaction with an Effector T4-Helper Lymphocyte An effector T4-helper lymphocyte, by way of its TCR and CD4, binds to the MHC-II/epitope on the activated B-lymphocyte. This, along with co-stimulatory signals that result from the binding of costimulatory molecules such as CD40 and B7 on the B-lymphocyte with their corresponding ligands on the activated T4-lymphocyte enable the T4-helper cell to release cytokines such as IL-4, IL-5, IL-6, and IL-10. These cytokines then bind to cytokine receptors on the activated B-lymphocyte triggering its proliferation into a large clone of identical B- lymphocytes. The clone of B-lymphocytes eventually differentiates into antibody-secreting B- lymphocytes and plasma cells. Some of the B-lymphocytes also differentiate into B-memory cells for heightened secondary response against that T-dependent antigen.
Differentiation of B-lymphocytes into Plasma Cells and B-Memory Cells The B-lymphocytes now differentiate into plasma cells that secrete large quantities of antibodies that "fit" the original epitope. Some B- lymphocytes differentiate into B-memory cells capable of anamnestic response.
Natural Killer Cells (NK Cells) Participate in both innate immunity and adaptive immunity. NK cells are lymphocytes that lack B-cell receptors and T-cell receptors. They are designed to kill certain mutant cells and virus-infected cells in one of two ways: 1. They kill cells to which antibody molecules have attached through a process called antibody-dependent cellular cytotoxicity (ADCC); and 2. They also are able to kill cells lacking MHC-I molecules on their surface.
Anamnestic (Memory) Response A subsequent exposure to that same antigen results in a more rapid production of antibodies, in greater amounts, and for a longer period of time. The primary response to a new antigen generally peaks at 5 - 10 days, however, because of the numerous circulating B-memory cells, the secondary anamnestic response peaks in only 1 - 3 days Because of clonal expansion and affinity maturation, there is now a pool of B-memory cells and pool of T4-memory cells enable an accelerated helper function.
MAJOR HISTOCOMPATIBILITY COMPLEX (MHC) The primary function of the immune system is the recognition and elimination of foreign cells and antigens that enter the body. Tissues and organs grafted from one individual to another of same species are recognized as foreign and rejected. MHC Molecules are originally characterized as the antigens responsible for the rejection of organs hence the name (histo or tissue compatibility). also known as human leukocyte antigens or HLA, are the products of a cluster of genes in the human DNA known as the major histocompatibility complex (MHC). These antigens are present on various human cells and enable T-lymphocytes to recognize epitopes and discriminate self from nonself.
A. MHC-I Molecules (Class I HLA Molecules) These molecules are made by all nucleated cells in the body. They bind peptide epitopes from endogenous antigens to enable immune recognition by T8-lymphocytes. Endogenous antigens are proteins found within the cytosol of human cells a. The TCRs and CD8 molecules on the surface of naive T8-lymphocytes are designed to recognize peptide epitopes bound to MHC-I molecules on antigen-presenting cells (APCs). b. The TCRs and CD8 molecules on the surface of cytotoxic T-lymphocytes (CTLs) are designed to recognize peptide epitopes bound to MHC-I molecules on infected cells and tumor cells.
Binding of Epitopes from Endogenous Antigens to MHC- I Molecules by an Antigen Presenting Cell (APC) 1. Exogenous antigens, such as viruses, are engulfed and placed in a phagosome. 2. Lysosomes fuse with the phagosome forming an phagolysosome. 3. During phagocytosis, some proteins escape from the phagosome or the phagolysosome and enter the cytosol of the APC and become endogenous antigens. 4. These endogenous antigens pass through proteasomes where they are degraded into a series of peptides.
5. The peptides are transported into the rough endoplasmic reticulum (ER) by a transporter protein called TAP. 6. The peptides then bind to the grooves of newly synthesized MHC-I molecules. 7. The endoplasmic reticulum transports the MHC-I molecules with bound peptides to the Golgi complex. 8. The Golgi complex, in turn, transports the MHC-I/peptide complexes by way of an exocytic vesicle to the cytoplasmic membrane where they become anchored. Here, the peptide and MHC-I/peptide complexes can be recognized by naive T8-lymphocytes by way of TCRs and CD8 molecules having a complementary shape.
B. MHC-II Molecules (Class II HLA Molecules) Class II HLA molecules are made primarily by antigen-presenting cells (APCs, eg, macrophages and dendritic cells) and B-lymphocytes. They bind peptide epitopes from exogenous antigens to enable immune recognition by T4- lymphocytes. MHC-II molecules have a deep groove that can bind peptide epitopes, from 10-30 but optimally from 12-16 amino acids long, from exogenous antigens. Exogenous antigens are antigens that enter from outside the body such as bacteria, fungi, protozoa, and free viruses. Binding of Epitopes from Exogenous Antigens to MHC-II Molecules in a Macrophage takes place in same manner as binding in MHC-I molecules but Here, the peptide and MHC-II complexes can be recognized by T4- lymphocytes by way of TCRs and CD4 molecules having a complementary shape.
An MHC- II Molecule on an Antigen-Presenting Cell Presenting a Bound Viral Epitope to a Naive T4-Lymphocyte with a Matching TCR/CD4 on its Surface Naive T4-lymphocytes via the unique T-cell receptors and CD4 molecules on their surface recognize peptide epitopes from exogenous antigens bound to MHC-II molecules on antigen presenting cells (APCs). Different T-cell receptors recognize different epitopes.
HLA and Disease association: Inflammatory disease including ankylosing spondylitis and several post infectious arthropathies are all associated with HLA B27 (Rheumatoid arthritis and HLA DR4). Inherited errors of metabolism such as 21 hydroxylase deficiency (HLA Bw47). Autoimmune disease including autoimmune endocrinopathy associated with certain DR alleles, HLA DRS.
IMMUNE RESPONSE The specific reactivity induced in a host by an antigenic stimulus is known as the immune response. In infectious disease it is generally equated with protection against invading microorganisms. Immune response includes reactions against any antigen, living or non- living. It may lead to consequences that are beneficial, indifferent or injurious to the host. It also includes the state of specific non reactivity (tolerance) induced by certain types of antigenic stimuli. The immune response can be of two types: 1. Humoral (Antibody mediated) response. 2. Cellular (cell mediated) response.
Two major branches of the adaptive immune responses are 1. Humoral immunity : Involves the production of antibody molecules in response to an antigen and is mediated by B-lymphocytes. 2. Cell-mediated immunity Involves the production of cytotoxic T-lymphocytes, activated macrophages, activated NK cells, and cytokines in response to an antigen and is mediated by T-lymphocytes.
Humoral immune response: The production of antibodies consists of three steps:  The entry of the antigen, its distribution and fate in the tissues and its contact with appropriate immunocompetent cells (afferent limb).  The processing of antigens by cells and the control of the antibody forming process (central functions).  The secretion of antibody, its distribution in tissues and body fluids and the manifestations of its effects (efferent limb).
Antibody production follows a characteristic pattern consisting of: 3 2 4 1 Primary Immune response. An antigen stimulus 1. Latent period or lag phase 2. Rise in titre of serum antibody 3. Steady state of antibody titre 4. Decline of antibody titre
The primary response is slow, sluggish and short lived with a long lag phase and low titre of antibodies that does not persist for long. The antibody formed - IgM In contrast the secondary response is prompt, and a much higher level of antibodies that lasts for long periods. The antibody formed - IgG. 4 2 3 1 A B C Effect of repeated antigenic stimulus. A, B, C antigenic stimulus 1. Primary immune response 2. Secondary immune response 3. Negative phase 4. High level of Ab following Booster Inj.
Cellular immune response: CMI refers to the specific immune response that does not involve antibodies. They include delayed hypersensitivity (DH), which results in injury rather than protection. CMI participates in the following immunological functions:  Delayed hypersensitivity.  Immunity in infectious diseases caused by obligate and facultative intracellular parasites. bacteria (for example, tuberculosis, leprosy, listeriosis, brucellosis) fungi (for ex. Histoplasmoses, coccidioidomycosis, bastomycosis), protozoa (ex. Leishmaniasis, trypanosomiasis) and viruses (for ex: measles, mumps).  Transplantation immunity and graft versus host reactions.  Immunological surveillance and immunity against cancer.  Pathogenesis of certain autoimmune diseases (thyroiditis encephalomyelitis).
THEORIES OF IMMUNE RESPONSE: Theories of immunity fall into two categories, instructive and selective. Instructive theories postulate that an immunocompetent cell is capable of synthesizing antibodies of any specificity. The antigen encounters an immunocompetent cell and instructs it to produce the complementary antibody. Selective theories, on the contrary, shift the emphasis from the antigen to the immunocompetent cell. They postulate that immunocompetent cells have only a restricted immunological range. The antigen exerts only a selective influence by stimulating the appropriate immunocompetent cell to synthesize an antibody.
Side chain theory: by Ehrlich (1900). Cells were considered to have surface 'receptors' capable of reacting with substances having complementary ‘side chains'. When foreign antigens are introduced into the body, they combine with those cell receptors, which have at complementary fit. This inactivates the receptors and interferes with the absorption of nutrients. As a compensatory mechanism, there is an overproduction of the same type of receptors, which spill over into the blood and circulate as antibodies. This theory explained elegantly the specificity of the antibody response. However, when Landsteiner demonstrated that antibodies could be formed not only against natural antigens but also against various synthetic chemicals, this theory was abandoned because a large number of receptors would be needed to for antibody specificity.
Direct template theories:  by Breinl and Haurowitz (1930), Alexander (1931) and Mudd (1932).  Antigen (or the antigenic determinant) enters antibody-forming cells and serves as a template against which antibody molecules are synthesized so that they have combining sites complementary to the antigenic determinant.  These are therefore known as ‘direct template’ theories. Indirect template theory:  by Burnet and Fenner (1949) proposed this instructive theory to explain the synthesis of antibody as an adaptive protein.  entry of the antigenic determinant into the antibody-producing cell induces in it a heritable change.  A 'genocopy' of the antigenic determinant was thus incorporated in its genome and transmitted to the progeny cells (indirect template). This theory explained specificity and the secondary response but became untenable with advances in the molecular biology of protein synthesis.
Natural selection theory:  By Jerne (1955)  This postulated that about a million globulin (antibody) molecules were formed in embryonic life, which covered the full range of antigenic specificities called by ‘natural antibodies’.  When an antigen was introduced, it combined selectively with the globulin that had the nearest complementary ‘fit’ and stimulates to synthesize the same kind of antibody. Selection was postulated at the level of the antibody molecule. It did not explain the fact that immunological memory resides in the cells, and not in serum
Clonal selection theory:  By Burnet (1957)  He shifted immunological specificity to the cellular level.  During immunological development, cells capable of reacting with different antigens were formed by a process of somatic mutation.  Elimination of ‘forbidden clones’ during embryonic life.  Their persistence or development in later life by somatic mutation could lead to autoimmune processes. Each immunocompetent cell was capable of reacting with one antigen introduced into the body.  Result of the contact - is cellular proliferation to form clones synthesizing the antibody. The clonal selection theory is more widely accepted than the other theories, though it is unable to account for all the features of the immune response.
CLASSIFICATION Immediate hypersensitivity (B cell or antibody mediated)  Anaphylaxis Type I  Atopy  Antibody mediated cell damage Type II  Arthus phenomenon  Serum sickness Type III Delayed hypersensitivity (T cell mediated)  Infection (tuberculin) type Type IV  Contact dermatitis type
Type I Hypersensitivity (Anaphylactic, IgE or reagin dependent)  Antibodies (‘cytotropic’ lgE antibodies) are fixed on the surface of tissue cells (mast cells and basophils) in sensitized individuals.  These cells carry large numbers of receptors called Fc ER receptors, IgE molecules attach to these receptors by their Fc end.  The antigen combines with the cell fixed antibody, this increases the permeability of the cells to calcium ions and leads to degranulation, with release of vasoactive amines which produce the clinical reaction.  Anaphylaxis: the acute, potentially fatal, systemic form  Atopy: the chronic or recurrent, nonfatal, typically localized form
Type- I Hypersensitivity: Production of IgE in Response to an Allergen The allergen enters the body and is recognized by sIg on a B- lymphocyte. The B-lymphocyte proliferates and differentiates into plasma cells that produce and secrete IgE against epitopes of the allergen.
Type- I Hypersensitivity: Allergen Interaction with IgE on the Surface of Mast Cells Triggers the Release of Inflammatory Mediators The next time the allergen enters the body, it cross-links the Fab portions of the IgE bound to the mast cell. This triggers the mast cell to degranulate, that is, release its histamine and other inflammatory mediators.
Anaphylaxis (ana = without, phylaxis = protection) classical immediate hypersensitivity reaction The inflammatory agents released, causes:  dilatation of blood vessels.  increased capillary permeability.  constriction of bronchial airways.  stimulation of mucous secretion.  stimulation of nerve endings.
PRIMARY MEDIATORS OF ANAPHYLAXIS Histamine:  formed by the decarboxylation of histidine  found in the granules of mast cells, basophils and in platelets.  stimulates sensory nerves, producing burning and itching.  Flare effect : vasodilatation and hyperemia by an axon reflex and Wheal effect : edema by increasing capillary permeability.  Histamine induces smooth muscle contraction in intestines, uterus and bronchioles.  secretogogue effect.
Serotonin (5-hydroxy tryptamine)  Derived by decarboxylation of tryptophan.  Found in the intestinal mucosa, brain tissue and platelets.  Smooth muscle contraction, increases capillary permeability and vasoconstriction. Eosinophil Chemotactic factors: (ECF-A)  Acidic tetrapeptides released from mast cell granules.  Contributes to the eosinophilia accompanying many hypersensitivity. Heparin Acidic mucopolysaccharide. Contributes to anaphylaxis in dogs, but apparently not in human
SECONDARY MEDIATORS OF ANAPHYLAXIS Prostaglandins and leukotrienes Derived by pathways from arachidonic acid, which is formed from disrupted cell membranes of mast cells and other leucocytes. The Lipoxygenase pathway leukotrienes, cyclo-oxygenase pathway prostaglandins and thromboxane. Slow Reacting Substance Of Anaphylaxis (SRS-A) produces low, sustained contraction of smooth muscles, identified as a family of leukotrienes (LTB4, C4, D4, E4). Prostaglandin F2a and thromboxane A2 are powerful, but transient, bronchoconstrictors. Prostaglandins also affect secretion by mucous glands, platelet adhesion, permeability and dilatation of capillaries and the pain threshold.
Treatment of Type I hypersensitivity epinephrine. 0.3 – 0.5ml of 1:1000 Epinephrine s.c. or i.m. with repeated doses, if required at 20 mts. intervals If not corrected, Hypoxia due to airway obstruction or related to cardiac arrhythmias is considered then O2 is given Epinephrine relaxes smooth muscle, constricts blood vessels, and stimulates the heart. It is used for severe systemic reactions. antihistamines diphenhydramine 50-100mg i.m. / i.v. Block the binding of histamine to histamine receptors on target cells. Nasally administered steroids. Corticosteroids are potent anti- inflammatory agents. sodium cromolyn. Sodium cromolyn prevents mast cells from releasing histamines. Aminophylline 0.25-0.5 gm i.v. for bronchospasm
Blocking Type-1 Hypersensitivity Using Monoclonal Antibodies Against IgE A new experimental approach to treating and preventing Type-I hypersensitivity involves, giving the person with allergies, the injections of monoclonal antibodies that have been made against the Fc portion of human IgE. This, in turn, blocks the attachment of the IgE to the Fc receptors on mast cells and basophils and the subsequent release of histamine by those cells upon exposure to allergen.
ATOPY: (out of place or strangeness) Refer to naturally occurring familial hypersensitivities of human beings, typified by hay fever and asthma. Inhalants (for example, pollen, house dust) Ingestants (for example, eggs, milk). Generally not good antigens when injected parenterally but induce IgE antibodies. It is difficult to induce atopy artificially. Often associated with a deficiency of IgA. This association has led to the suggestion that IgA deficiency may predispose to atopy. Clinical features includes conjunctivitis, rhinitis, gastrointestinal symptoms and dermatitis following exposure through the eyes, respiratory tract, intestine or skin, respectively.
Type II (cytotoxic and cytolytic)  These reactions involve a combination of IgG (or rarely IgM) antibodies with the antigenic determinants on the surface of cells leading to cytotoxic or cytolytic effects. Cell or tissue damage occurs in the presence of complement or mononuclear cells. Mechanism: Either IgG or IgM is made against normal self antigens as a result of a failure in immune tolerance or a foreign antigen resembling some molecule on the surface of host cells enters the body and IgG or IgM made against that antigen then cross reacts with the host cell surface.
Opsonization During Type-II Hypersensitivity IgG reacts with epitopes on the host cell membrane. Phagocytes then bind to the Fc portion of the IgG and discharge their lysosomes.
MAC Lysis During Type-II Hypersensitivity IgG or IgM reacts with epitopes on the host cell membrane and activates the classical complement pathway. Membrane attack complex (MAC) then causes lysis of the cell.
Examples include:  AB and Rh blood group reactions;  Autoimmune diseases such as: Rheumatic fever where antibodies result in joint and heart valve damage; Idiopathic thrombocytopenia purpura where antibodies result in the destruction of platelets; Myasthenia gravis where antibodies bind to the acetylcholine receptors on muscle cells causing faulty enervation of muscles; Goodpasture's syndrome where antibodies lead to destruction of cells in the kidney; Graves' disease where antibodies are made against thyroid- stimulating hormone receptors of thyroid cells leading to faulty thyroid function; Multiple sclerosis where antibodies are made against the oligodendroglial cells Some drug reactions Type II hypersensitivity also participates in early transplant rejections.
TYPE III (IMMUNE COMPLEX - MEDIATED) A hypersensitivity resulting from large quantities of soluble antigen- antibody complexes passing between endothelial cells of the blood vessels and becoming trapped on the surrounding basement membrane. The antigen/antibody complexes then activate the classical complement pathway. This may cause: a. massive inflammation b. influx of neutrophils c. MAC lysis of surrounding tissue cells d. aggregation of platelets
Type-III Hypersensitivity: Immune Complex Large quantities of soluble antigen-antibody complexes form in the blood and are not completely removed by macrophages. These antigen-antibody complexes lodge in the capillaries between the endothelial cells and the basement membrane. The antigen-antibody complexes activate the classical complement pathway and complement proteins and antigen-antibody complexes attract leukocytes to the area. The leukocytes then discharge their killing agents and promote massive inflammation. This leads to tissue death and hemorrhage
Examples include:  Serum sickness, a combination type I and type III  Hypersensitivity;  Autoimmune acute glomerulonephritis;  Rheumatoid arthritis;  Systemic lupus erythematosus;  Some cases of chronic viral hepatitis; and  Skin lesions of syphilis and leprosy.
ARTHUS REACTION Arthus (1903) observed that when; rabbits were repeatedly injected subcutaneously with normal horse serum, the initial injections had no local effect but with later injections, there occurred intense local reaction consisting of edema, induration and hemorrhagic necrosis. This is known as the Arthus reaction The tissue damage is due to formation of antigen-antibody precipitates causing complement activation and release of inflammatory molecules. This leads to increased vascular permeability and infiltration of the site with neutrophils. Leucocyte-platelet thrombi are formed that reduces the blood supply and lead to tissue necrosis. For example, intrapulmonary Arthus-like reaction to inhaled antigens, such as thermophilic actinomycetes from mouldy hay or grain causes Farmer's lung and other types of hypersensitivity pneumonitis.
SERUM SICKNESS by von Pirquet and Schick (1905), this appeared 7-12 days following single injection of a high concentration of foreign serum such as the diphtheria antitoxin. The clinical syndrome consists of fever, lymphadenopathy, spleenomegaly, arthritis, glomerulonephritis, endocarditis, vasculitis, urticarial rashes, abdominal pain, nausea and vomiting. The plasma concentration of complement falls due to massive complement activation and fixation by the antibody complexes. The disease is self-limited. The latent period of 7-12 days is required only for serum sickness following a single injection. With subsequent injections, the disease manifests earlier. Serum sickness differs from other types of hypersensitivity reaction in that a single injection can serve both as the sensitizing dose and the shocking dose.
TYPE IV (DELAYED HYPERSENSITIVITY) It is cell-mediated rather than antibody-mediated. Mechanism: T8-lymphocytes become sensitized to an antigen and differentiate into cytotoxic T-lymphocytes, while Th1 type T4-lymphocytes become sensitized to an antigen and produce cytokines. CTLs, cytokines, and/or macrophages then cause harm rather than benefit.
Examples include: tuberculosis, leprosy, smallpox, measles, herpes infections, candidiasis, and histoplasmosis; the skin test reactions seen for tuberculosis and other infections; contact dermatitis like poison ivy; type-1 insulin-dependent diabetes multiple sclerosis, where T-lymphocytes and macrophages secrete cytokines that destroy the myelin sheath that insulates the nerve fibers of neurons; chronic transplant rejection as seen in host versus graft rejection or graft versus host rejection.
Tuberculin (infection) type When a small dose of tuberculin is injected intradermally in an individual sensitized to tuberculoprotein by prior infection or immunisation, an indurated inflammatory reaction develops at the site within 48-72 hours. In unsensitized individuals, the tuberculin injection provokes no response. The tuberculin test therefore provides useful indication of the state of delayed hypersensitivity (cell mediated immunity) to the bacilli. Tuberculin type hypersensitivity develops in many infections with bacteria, fungi, viruses and parasites, especially when the infection is subacute or chronic and the pathogen intracellular.
Contact dermatitis type Delayed hypersensitivity usually occurs due to skin contact with a variety of substances–  Sensitization is particularly liable when contact is with an inflamed area of skin and when the chemical is applied in an oily base.  The substances involved are in themselves not antigenic but may acquire antigenicity on combination with skin proteins. Sensitization requires percutaneous absorption.  Langerhans cells of the skin capture locally applied hapten and migrate to the draining lymph nodes, present hapten along with MHC molecules, to T cells. The sensitized T cells travel to the skin site, where on contacting the antigen they release various lymphokines
 Contact with the allergen in a sensitized individual leads to ‘contact dermatitis’, characterized by maculopapular lesions to vesicles that break down, leaving behind raw weeping areas typical of acute eczematous dermatitis.  Hypersensitivity is detected by the ‘patch test’. The allergen is applied to the skin under an adherent dressing. Sensitivity is indicated by itching appearing in 4-5 hours, and local reaction, which may vary from erythema to vesicle or blister formation, after 24-28 hours. Metals : nickel and chromium, Chemicals : dyes, picryl chloride, dinitrochlorobenzene, Drugs : penicillin
Shwartzman reaction Shwartzman (1928) observed that if a culture filtrate of S. typhi is injected intradermally in a rabbit, followed 24 hours later by the same filtrate intravenously, a hemorrhagic necrotic lesion develops at the site of the intradermal injection. The intradermal and intravenous injections need not be of the same or even related endotoxins. This absence of specificity and the short interval between the two doses preclude any immunological basis for the reaction. The four types of immunopathogenic mechanisms described are not mutually exclusive. Any given hypersensitive reaction may comprise the components of more than one, or all of these mechanisms.
AUTOIMMUNITY  The immune reaction to self-antigens  Autoimmunity is a condition in which structural or functional damage is produced by the action of immunologically competent cells or antibodies against the normal components of the body.  Autoimmunity literally means ‘protection against self’ but it actually implies injury to self. It is also known as ‘Autoallergy’.  Autoimmunity also implies loss of self-tolerance.
Features of diseases of autoimmune origin 1. An elevated level of immunoglobulins 2. Demonstrable autoantibodies 3. Deposition of immunoglobulins at sites of election 4. Accumulation of lymphocytes and plasma cells at site of lesion 5. Benefit from immunosuppressive therapy like corticosteroid 6. Occurrence of more than one type of autoimmune lesion 7. A genetic predisposition towards autoimmunity 8. Incidence higher among females 9. Chronicity. Usually nonreversible
Immunologic tolerance: is a state in which an individual is incapable of developing an immune response against a specific antigen. Self- tolerance specifically refers to a lack of immune responsiveness to one’s own tissue antigens. Central tolerance: This refers to the deletion of self-reactive T and B- lymphocytes during their maturation in central lymphoid organs. Any developing T cell or B cell that expresses a receptor for such self- antigen is deleted by apoptosis. Peripheral tolerance: Self-reactive T cells that escape negative selection in the thymus can potentially dangerous outside in peripheral lymphoid organs. Anergy: This refers to prolonged or irreversible inactivation (rather than apoptosis) of lymphocytes induced by encounter with antigens under certain conditions.
Mechanisms of Autoimmune Disease Breakdown of one or more of the mechanisms of self-tolerance can unleash an immunologic attack on tissues that leads to the development of autoimmune diseases. Failure of tolerance Failure of Activation induced Cell Death: Defects in this pathway may allow persistence and proliferation of autoreactive T cells in peripheral tissues, which may lead to autoimmune disease. Breakdown of T-Cell Anergy: Autoreactive T cells that escape central deletion are rendered anergic when they encounter self-antigens in the absence of costimulation.
Molecular Mimicry: Some infectious agents share epitopes with self- antigens, and an immune response against such microbes will elicit similar responses to the cross-reacting self-antigen. Polyclonal B cell activation: While an antigen generally activates only its corresponding B cell, certain stimuli nonspecifically turn on multiple B cell clones. These polyclonal antibodies are IgM in nature. Release of Sequestered antigens: Any self-antigen that is completely sequestered during development is likely to be viewed as foreign if subsequently introduced to the immune system. Spermatozoa and ocular antigens fall into this category.
AUTOIMMUNE DISEASES Localized Hemolytic (organ specific) Systemic Transitory (non organ specific)
HEMOLYTIC AUTOIMMUNE DISEASES 1. Autoimmune hemolytic anemias: Autoantibodies against RBC are demonstrable. Two group of anemias are: Cold autoantibodies: Complete agglutinating antibodies belonging to IgM class Warm autoantibodies: Incomplete nonagglutinating antibodies belonging to IgG class 2. Autoimmune thrombocytopenia: Autoantibodies directed against platelets eg. In Idiopathic thrombocytopenia purpura 3. Autoimmune leucopenia: nonagglutinating antileucocyte antibodies in serum of SLE and RA patients
LOCALIZED (ORGAN SPECIFIC) AUTOIMMUNE DISEASES 1. Autoimmune diseases of thyroid gland: Hashimoto’s disease and Thyrotoxicosis (Graves’ disease) 2. Addison’s disease: Antibodies directed against cells of Zona glomerulosa 3. Autoimmune Orchitis: Antibodies against sperms and germinal cells 4. Myasthenia Gravis: Antibody against acetyl choline receptors on myoneural junctions of striated muscles
5. Autoimmune diseases of Eye: In cataract surgery autoimmune response to lens protein leads to intraocular inflammation (phacoanaphylaxis) 6. Pernicious anemia: Antibodies directed against parietal cell of gastric mucosa and intrinsic factor 7. Autoimmune disease of Skin: Pemphigus vulgaris, Bullous pemphigoid and dermatitis herpetiformis
SYSTEMIC (NONORGAN SPECFIC) AUTOIMMUNE DISORDERS 1. Systemic lupus erythematosus: Autoantibodies directed against: Cell nuclei, intracytoplasmic cell constituents, immunoglobulins and thyroid gland 2. Rheumatoid arthritis: Presence autoantibody called as Rheumatoid factor against the Fc fragment of immunoglobulin 3. Polyarteritis nodosa 4. Sjogren’s syndrome TRANSITORY AUTOIMMUNE PROCESSES Includes conditions like Anemias, thrombocytopenias or nephritis that follow infection or drug therapy. They induces antigenic alteration in self antigens. Disease is transient.
ORAL IMMUNOLOGY The health of the mouth is dependent on the integrity of mucosa, saliva, gingival crevicular fluid and their immune components, which does not normally allow microorganisms to penetrate. The oral tissues are drained by an anatomically well defined collection of extraoral lymph nodes and intraoral lymphoid tissue aggregations. I The tonsils (palatine and lingual) 2 Salivary gland, plasma cells and lymphocytes 3 Gingival aggregation of plasma cells, lymphocytes, macro-phages 4 The scattered submucosal lymphoid cells
The functional significance of the intraoral lymphoid tissue has not been clearly defined. It appears that  The tonsils guards the entry into the digestive and respiratory tracts  The gingival lymphoid aggregation responding to the dental bacterial plaque accumulation.  The salivary lymphoid tissue for secretary IgA synthesis and protection against infection within the salivary gland. The secretary IgA in saliva may combine with microorganisms and prevent their adherence to the mucosal surface.
Sources of Immunoglobulin in whole saliva
Synthesis, assembly and secretion of IgA
Local and systemic immunity affecting the tooth Tooth surface is influenced by both local salivary and systemic immune mechanisms. The division between the two immune mechanisms occurs near the gingival margin, the only site of the body where an interphase can be found between the local secretory and systemic immune mechanisms. The salivary domain depends on the function of secretary IgA and the gingival domain is controlled by immune components found in blood.
Blood Crevicular Gingival fluid crevicular IgG, IgM, IgA domain Protein Complement Enzymes Electrolytes Polymorphs Oral fluid B, T Lymphocytes Macrophages sIgA IgG, IgA Salivary Proteins domain Enzymes sIgA Electrolytes Proteins Polymorphs Enzymes Electrolytes Salivary Salivary Salivary gland fluid domain Humoral and Cellular components in crevicular, salivary and oral fluids
IMMUNOLOGY OF DENTAL BACTERIAL PLAQUE DENTAL PLAQUE COMPONENTS CARIOGENIC IMMUNOPOTENTIATING AND PERIODONTOPATHIC MICRO-ORGANISMS IMMUNOSUPPRESIVE AGENTS MICRO-ORGANISMS Streptococcus mutans Lipopolysaccharides, Dextrans, Actinomyces, Actinomyces viscosus Levan, Lipoteichoic acid Actinobacillus, Lactobacilli Veillonella, Eikenalla, Spirochaetes IMMUNE RESPONSE ANTIBODY COMPLEMENT CHEMOTAXIS: PHAGOCYT- T- AND B - ACTIVATION PMNL, OSIS: PMNL LYMPHOCYTES IgA, IgM, Classical and MACROPHAGES Killing, Suppression, IgA, sIgA, Alternative Lysosomal Proliferation, IgE pathway enzymes Memory, Help CARIES GINGIVITIS, PERIODONTITIS
IMMUNOLOGY OF PERIODONTAL DISEASE Local immunopathological and systemic immune responses during four stages of development of periodontal disease
TYPE I TYPE II TYPE III TYPE IV IgE Antibodies Immune complex Lymphocytes Mast cell Opsonic Cell lysis: ADCC Complement Platelet Lymphokines: adherence C5 – 9 activation aggregation Mitogenic factor MIF Lymphotoxin OAF Vasoactive Phagocytes Histamine, Micro thrombi Amines Chemotaxis Vocative of polymorphs amines Killing The complex nature of immune responses in immunopathogenesis of periodontal disease
IMMUNOLOGY OF DENTAL CARIES Serum IgG, salivary IgA and IgM antibodies and cell mediated immunity to Streptococcus mutants can be correlated with the DMF index of caries. Principal immunological mechanisms of protection against caries includes Direct immunization of the minor salivary glands or of the gut associated lymphoid tissue, so that salivary IgA antibodies thus secreted prevent S. mutans from adhering to the tooth surface and thereby prevent caries. Humoral and cellular components elicited by systemic immunization. Antibodies, complement, PMN, lymphocytes and macrophages pass from the gingival blood vessels to the gingival domain of the tooth and mediates IgG-induced opsonization, binding and phagocytosis. Local gingivo-salivary immunization with synthetic peptides induces a dual gingival IgG and salivary IgA antibodies to S. mutans.
Time TOOTH CARIES Bacteria Sugar NO CARIES Antibodies Five principles factors in the development of caries
Local passive immunization with monoclonal antibodies against S. mutans prevents colonization of this organism and is a local non-invasive method of prevention of caries.
4 – phase hypothesis of mechanism of prevention of colonization of S. mutans by Specific Monoclonal Antibodies
Four preventive immuno – microbiological measures from gestation to childhood
IMMUNOLOGY OF ORAL INFECTIONS Immunopathology of Herpes virus infection Herpes simplex virus is a DNA virus 2 types: Type 1 and Type 2 3 genes: Alpha, beta and gamma Beta gene codes for viral glycoproteins gB, gC, gD and gE.  gB is involved in viral penetration of the cell membrane,  gC constitutes the C3b receptor (binding the activated C3b),  gF is the Fc receptor for IgG and  Antibodies against gD neutralize HSV and block penetration of HSV.
Primary herpetic infection The incubation period is between 2 and 7 days. Within the first week of onset of clinical manifestations sensitized lymphocytes to HSV can be detected in the peripheral blood but no significant antibodies or macrophage migration inhibition factor (MIF). After 2 weeks significant antibody titres and MIF appear. Recovery from infection coincides therefore with the appearance of antibody and of MIF. Recurrent HSV infection A deficiency of MIF production and decreased cytotoxicity by sensitized CD8 cells may play a part in re-current infection. CD4-T cells produce interferon and decreased interferon production has been correlated with an increased fre-quency of recurrent HSV infections. Due to selective deficiency in cell-mediated immunity
IMMUNOLOGICAL FEATURES OF CANDIDIASIS Candidiasis is seen in patient with defective generation or differentiation of lymphoid stem cells T-cell immune responses prevents muco-cutaneous candidiasis and serum IgG and IgM antibodies prevents systemic candidiasis. Immunodeficiencies of cellular, humoral or phagocytic components play an important part in candidiasis. Oral candidiasis is found in patients with AIDS who have a deficiency of CD4 cells. Patients with B-lympho-cyte defects alone are not susceptible to candidiasis, unless they also have a concurrent T-cell deficiency, as in the severe combined immunodeficiency syndrome.
IMMUNLOGICAL AND AUTOIMMUNE DISORDERS OF ORAL MUCOSA Recurrent aphthous ulcers Patients with RAU show an association with HLA-B12 and it offers immunogenic basis for development of the disease Cell mediated immunity is involved in RAU This induces type III and type IV hypersensitivity reactions Immunohistological investigation reveals increase in no. of CD4 and CD8 cells, Langerhans cells and macrophages.
Pemphigus vulgaris Association with DR4 or DRw6 Autoantibodies to intercellular substance of epithelial cells (IgG type) circulating and bound to keratinocytes at site of disease Epithelial cells with autoantibodies release plasminogen activators which activate plasmin and leads to acantholysis Benign mucous membrane pemphigoid (BMMP) Presence of circulating anti-basement membrane antibodies (IgG, IgA and IgM) with or without complement Autoantibodies react with the lamina lucida of basement membrane
Lichen planus Histology shows a increase in Langerhans cells and well defined T-cell (CD4 and CD8) infiltration of lamina propria Lichen planus usually develops in mouth and/or skin of patients in which Graft versus host reaction takes place Variety of drugs can induce lichenoid reactions in the mouth Sjogren’s syndrome Presence of Antinuclear factor Organ specific antibodies Salivary duct antibodies
IMMUNE RESPONSES IN DENTAL PULP AND PERIAPICAL TISSUES Pulp of normal tooth contains T-cells with the CD4 and CD8 cells in a ratio of 1:2 reverse to that found in circulation (2:1) B-cell are not found in normal pulp, so they have to home to pulp during inflammatory reaction Pulp and periapical tissues possess the cellular components to mount hypersensitivity reactions namely Type III, II and I Immune responses to dental caries leads to development of Chronic pulpitis and periapical granulomas Cysts shows plasma cell infiltration in cyst conc. Of IgG, IgM and IgA in cyst fluid
IMMUNE FUNCTION TESTS A careful history and physical examination will usually indicate whether the major problem involves the Antibody – Complement phagocyte system or Cell mediated immunity
HUMORAL IMMUNITY TEST COMMENT Immunoglobulin survey (serum protein General assessment of B cell function electrophoresis, Ig quantification) To assess levels of IgG, A, M, D and E Isohemagglutinin titer (anti-A, anti-B) General indication of IgM production Titers before and after immunization Demonstrates the in vivo ability to with a specific vaccine (TT, respond to known antigen pneumovax, Typhoid – paratyphoid) B cell enumeration by surface sIg or Measures the no. of circulating B cells flow cytometry Biopsy of bone marrow, lymph node, Assessment of presence and/or or gut location of lymphocytes (germinal centers, plasma cells)
CELL MEDIATED IMMUNITY TEST COMMENT Peripheral WBC count and General assessment of T cell morphology presence T cell enumeration by nonimmune Measures the total no. T cells in rosetting or flow cytometry (CD3) peripheral blood Enumeration T cell subsets (CD4, The TH / TS ratio is usually 2:1 CD8) Measurement of lymphokine Assessment of T cell ability to secrete production (MIF, IL-2) lymphokine Response to phytohemagglutinin or Evaluation of T cell ability to undergo mixed lymphocyte culture blastogenesis
Response to phytohemagglutinin or Evaluation of T cell ability to undergo mixed lymphocyte culture blastogenesis Delayed hypersensitivity skin testing to Assessment of in vivo function of T cell recall antigens (PPD, histoplasmin, to a previously encountered antigen Candida, mumps, streptokinase) Dinitrochlorobenzene skin (DNCB) Assessment of in vivo function of T cell sensitization to respond to a newly encountered antigen Biopsy of lymph node Assessment of the presence of T cell in thymus – dependent areas Complement CH50 assays (classic and alternative pathway) Phagocyte function Reduction of Nitroblue tetrazolium Chemotaxis assays, Bactericidal activity
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