Chapter 17
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  • 1. Chapter 17 Adaptive (Specific) Defenses
  • 2. Adaptive (Specific) Defenses
    • Recognizes specific foreign substances and immobilizes, neutralizes or destroys them
    • 3 characteristics of specific immunity
        • Antigen-specific – recognizes particular antigens
        • Systemic – not restricted to infection site
        • Has memory
    • Dual nature – two types of immune response
    • 2 divisions of specific immunity
        • Humoral (antibody mediated) immunity
          • Involves antibodies found in body fluids ( humors)
        • Cellular (cell mediated ) immunity
          • Protection comes from living cells (Lymphocytes)
    • Immunity may be innate (genetic) or acquired
      • Acquired naturally or artificially
  • 3. Active or Passive Immunity
    • Active immunity – when B cells encounter antigens and produce antibodies against them
      • Naturally acquired – antibodies produced due to infection
      • Artificially acquired – antibodies produced due to vaccine
    • Passive immunity
      • Naturally acquired – antibodies cross placenta and breast milk from mother to fetus – baby is protected from all antigens the mother has been exposed to
      • Artificially acquired – serum containing antibodies is infused – provide immediate protection, but effect is short lived (2-3 weeks) - used to treat snake bits, rabies, tetanus ect...
  • 4.  
  • 5.
    • Antigens – Surface molecules involved in identification
      • Large, complex molecules found on the surface of viruses and cells
      • Mobilize immune system; provoke immune response
      • Most antigens have several epitopes
        • antibody binding site
    • Haptens – small molecules that can bind to a larger protein and act as epitopes for the protein
      • Neither protein nor hapten can act as an antigen alone
    • Antibodies – protein produced in response to an antigen that is capable of binding to that antigen
    • Titer - the quantity of a substance required to illicit a response
      • Antibody titer is the amount of an antibody required to bind to and neutralize a particular quantity of antigen
  • 6.
    • Antibodies recognize and react with antigenic determinants or epitopes
  • 7.  
  • 8.
    • MHC Proteins (Self-Antigens) – proteins that cover the external surface of our cells
      • not foreign or antigenic to us but very antigenic to others
        • Blood groups
      • Specific group of glycoproteins that mark cells as self
      • No 2 people (except identical twins) have the same MHC proteins
      • 2 Groups of MHC proteins
        • Class 1 MHC proteins – found on all body cells
        • Class II MHC proteins – found only on specific cells involved in immune response
  • 9. Cells and Tissues of Immune System
    • 3 critical types of cells
      • Antigen presenting cells (APCs)
        • Do not respond to specific antigens
        • Play an auxiliary role
      • B Lymphocytes (B cells)
        • Plasma cells - Secrete antibodies
        • Other B cells become memory cells
      • T Lymphocytes (T cells)
        • Do not produce antibodies
        • Seek out and destroy pathogens
  • 10.
    • Lymphocytes are white blood cells
      • made in red bone marrow
    • It becomes a T cell or B cell based on where it becomes immunocompetent (able to recognize specific antigens)
      • T cells – thymus
        • Also develop self-tolerance; T cells that bind to strongly with self antigens (MHC proteins) are destroyed
      • B cells – bone marrow
      • Bone marrow and thymus are primary lymphoid organs
        • all others are secondary lymphoid organs (spleen, nodes)
      • Immunocompetent B and T cells display unique receptors on their surface that bind with specific antigens
        • bind with only 1 antigen type
        • Genetics determine which antigens the immune system will recognize
  • 11.  
  • 12.
    • Antigen-Presenting Cells (APCs)
      • Major role is to engulf foreign particles and present fragments on their own surface
        • Signal flags to be recognized by T cells
        • Dendritic cells, Langerhan’s cells, macrophages and activated B cells
        • Dendrites and macrophages also secrete soluble proteins that activate T cells
  • 13. Humoral Immune Response
    • Antigen challenge – 1 st encounter between lymphocyte and antigen
      • If it is a B cell, humoral immune response is initiated and antibodies are produced against the antigen
      • The naïve but immunocompetent B cell is activated when the antigen binds to its surface receptors – antigen specific
      • This activity triggers clonal selection
        • B cells multiply rapidly to form identical clones
      • Most clones become plasma cell which produce antibodies (2000 per sec) for 4 – 5 days then die
      • Other clones become long-lived memory cells
  • 14. Immunological Memory
    • Primary immune response
      • Occurs on the 1 st exposure to an antigen
      • Typically has a lag time of 6-7 days
      • Antibody production peaks in about 10 days then begins to decline
    • Secondary immune response
      • Occurs when re-exposed to same antigen
      • Faster, more prolonged, more effective
      • Memory cells provide immunological memory
      • Antibody production peaks in 2-3 days and can persist for weeks or months
  • 15.  
  • 16. Antibodies
    • Immunoglobulins (Igs) - gamma globulin part of blood proteins
      • Soluble proteins secreted by B cells in response to antigens
        • Capable of binding with that specific antigen
      • Each antibody has the same basic structure
        • 4 looping polypeptide chains
          • 2 heavy chains and 2 light chains
          • Combine to for a Y shaped molecule (antibody monomer)
          • Each chain has a variable and constant region
          • Constant region determines class of antibody
          • Variable regions form antigen-binding site
          • Each monomer has 2 antibody-binding sites
          • Monomers combine to form different antibodies
  • 17.  
  • 18. Antibody Classes
    • Five major classes – IgM, IgA, IgD, IgG, IgE (MADGE)
      • IgM – fixes complement
      • IgA – found primarily in mucus and other body secretions
      • IgD – bound to B cell surface; acts as a receptor site
      • IgG – most abundant; crosses the placenta; fixes complement
      • IgE – rarely found in blood; active in allergies
  • 19.
    • Pentamer
    • 5-10% of serum antibodies
    • Found primarily on B cell membranes
    • Fix complement
    • Agglutinates microbes
    • First Ab produced in response to infection
    • ABO blood group Ab
    IgM antibodies
  • 20.
    • Dimer
    • 10-15% of serum antibodies
    • Found primarily in mucus and other body secretions
      • Abundant in colostrum
    • Fix complement
    IgA antibodies
  • 21.
    • Monomer
    • 0.2% of serum antibodies
    • Bound to B cell surface
      • acts as a receptor site
      • Beyond that function is unknown
    IgD antibodies
  • 22.
    • Monomer
    • 80% of serum antibodies
    • Fix complement
    • Cross placenta
    • Present in milk
    • Enhance phagocytosis; neutralize toxins & viruses
      • protects fetus & newborn
    IgG antibodies
  • 23.
    • Monomer
    • 0.002% of serum antibodies
    • Found on mast cells and basophils
    • Allergic reactions
    • Lysis of parasitic worms
    IgE antibodies
  • 24. Antigen-Antibody Reactions
    • Antibodies themselves can’t destroy invaders
      • they inactivate them and tag them for destruction by forming an antigen-antibody complex
    • 4 defensive mechanisms they use
      • neutralization
      • Agglutination
      • Precipitation
      • Complement fixation (only IgG and IgM and IgA)
        • PLAN of action – precipitation, lysis (by complement), agglutination and neutralization
  • 25.
    • Complement fixation and activation
      • Antibodies bind to cells changing their shape to expose complement binding sites on their constant regions
      • Triggers complement fixation onto antigenic cell’s surface resulting in cell lysis
      • Molecules released during complement fixation also amplify inflammation and induce phagocytosis
    • Neutralization
      • Antibodies block specific sites on viruses or bacterial toxins
      • Loses its toxic effect – can’t bind to receptors on tissue cells to cause damage
  • 26.
    • Agglutination
      • Antigen-antibody complexes can be cross-linked into large lattices
      • Causes clumping of antigenic cells
    • Precipitation
      • Soluble molecules (instead of cells) are cross-linked into large complexes that settle out of solution
      • These immobilized antigen molecules are easier to capture and engulf by phagocytes
  • 27.  
  • 28. Cell Mediated Response
    • T cells mediate cellular immunity
      • More complex then B cells
      • 2 major classes of T cells
        • Helper T cells (T H )
        • Cytotoxic (killer) T cells (T C )
      • There are also delayed hypersensitivity T cells (T DH ), suppressor T cells (T S ) and memory T cells (T M )
      • T cells are unable to see free antigens
        • Recognize and respond to processed fragments of proteins displayed on body cell surfaces (APCs)
      • T cells are activated when a recognized antigen binds to their surface receptor
      • T cells have a double recognition process
        • Recognize non-self antigens and self (MHC proteins)
  • 29. Specific T Cell Roles
    • Helper T Cells – regulatory cells
      • Chemically or directly stimulate proliferation of other T cells and B cells
      • Do not bind to antigen themselves
      • Produce cytokines that provide signal to attract other immune cells
    • Cytotoxic T Cells – killer T cells
      • Directly attack and kill other cells, primarily virus infected cells, but also attack bacteria infected tissues
      • Binds to target cell; inserts perforin into the plasma membrane; then detaches from target cell – lethal hit resulting in cell lysis
      • Perforin molecules polymerize causing cell lysis
      • Some release other chemicals like lymphotoxin which targets DNA or tumor necrosis factor
  • 30.  
  • 31.
    • Other T cells
      • Suppressor T cells
        • Regulatory cells; release cytokines that suppress T cell and B cell activity
        • Vital in stopping immune response after an antigen has been successfully inactivated or destroyed
      • Delayed-Hypersensitivity T Cells
        • Instrumental in promoting allergic responses
      • Each type of T cell has a role in the immune response
  • 32. Chapter 18 Immunological Disorders
  • 33.
    • Factors that modify immune response
      • Compromised host
      • Immunization
        • Vaccine or toxoid
    • Immunological Disorders – inappropriate or inadequate immune response
      • Hypersensitivity
        • Immune system reacts in an exaggerated or inappropriate way to a foreign substance
      • Immunodeficiency
        • Inadequate response due to defects in B cells or T cells
      • Auto Immune Disorders
        • Become hypersensitive to specific self antigens
      • Transplantation
        • Immune system attacks transplanted cells or tissues
  • 34.
    • Hypersensitivities
      • An allergen is an antigen that evokes a hypersensitivity response
        • Pollen, foods, insect stings, pet dander
      • Type I – immediate allergic response
        • Anaphylaxis – from prior exposure to antigen
      • Type II – cytotoxic effects
        • Typically transfusion reaction or childbirth
      • Type III – immune complex
        • Antigens in vaccines
      • Type IV – cell-mediated or delayed
        • Exposure to foreign substances, pathogens, transplanted tissues
  • 35. Type I – immediate allergic response
    • Sensitization
      • B cells are activated
    • Production of IgE antibodies
      • Bind to mast cells and basophils
    • Allergen-IgE reactions
      • As allergins bind to IgE antibodies mast cells and basophils release histamine, prostagladins and leukotrienes
    • Local and Systemic effects
      • Capillary dilation and increased permeability, airway constriction, mucus secretion, pain and itching
  • 36.
    • Normal human red blood cells have surface antigens that are genetically determined that form the basis for the 4 blood types
    • A transfusion reaction will occur when a patient is given blood cells displaying the wrong antigen
    • A person has no antibodies against their normally present antigen
      • If you have the A antigen then you have type A blood and DO NOT have antiA antibodies
      • You would however have antiB antibodies
      • If you received cells with B antigens they would be clumped and destroyed (agglutination)
    Type II – Cytotoxic
  • 37.  
  • 38.
    • Erythroblastosis fetalis or hemolytic disease of the newborn is another example of a cytotoxic reaction
    • Red blood cells also have rh antigens
      • If you have the antigen you are rh+ if you do not have it you are rh-
    • When an rh – mom carries an rh+ baby she is exposed to a foreign antigen and she begins to make anti-rh antibodies
      • The 1 st baby will be uneffected, but if she get pregnant a 2 nd time and the baby is rh+ her body will attack the baby’s red blood cells
      • If the 2 nd baby is rh- there is no problem
  • 39.
    • Immunodeficiences
      • both congenital and acquired conditions where production or function of immune cells, phagocytes or complement is abnormal
      • Severe combined immunodeficiency syndrome (SCID)
        • boy in the bubble
        • congenital
      • Acquired immune deficency syndrome (AIDS)
        • Caused by a virus (HIV- human immunodeficiency virus)
  • 40.
    • Autoimmune Diseases
      • immune system loses the ability to tell self from non-self
      • Turns on itself
      • Multiple sclerosis – destroys white matter of brain and spinal cord
      • Systemic lupus – systemic disease affects most body systems
      • Rheumatoid arthritis – destroys joints
  • 41. Organ Transplants and Rejection
    • Four major varieties
      • Autografts – tissues transplanted from one body site to another in the same person
      • Isografts – grafts donated by a genetically identical person – only identical twins
      • Allografts – transplanted from individuals who are genetically similar – same species
      • Xenografts – grafts taken from another animal species – baboon heart
      • Immune rejection presents a major problem