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Uploaded byNistarini College, Purulia (W.B) India
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Comprehensive Overview of Basic Immunology and Body Defence Mechanisms

Explores health definitions, disease, and detailed innate and acquired immunity mechanisms including physical barriers, cellular responses, and immune system functions.

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BASIC IMMUNOLOGY Dr. Nandadulal Sannigrahi, Associate Professor, Department of Botany, Nistarini college, Purulia D.B. Road, Purulia, INDIA (W.B)
HEALTH AND DEFENCE MECHANISMS  Although health is an essential and important issue for the progress of developing countries, the definition and goals of health tend to be seen as very important in this consequences.  According to the World Health Organization’s (WHO) definition, health is “a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.”  Health development encompasses all the elements that are necessary for the achievement of such a state of being. In this context, a wide variety of disciplines have some relation to health; specifically, these disciplines include epidemiology, biology, public health and medical science as well as demography, economics, and international health.  The Declaration of Alma-Ata of 1978 which introduced the concept of Primary Health Care (PHC) marked a turning point in the approach and goals of international aid in the field of health in developing countries. PHC made explicit the importance of primary health care in developing countries. In addition, it calls for prioritizing local health care needs and
HEALTH AND DEFENCE MECHANISMS  fully utilizing locally-available resources to provide health care services to meet those needs. This approach represents a dramatic departure from the previous goal of international aid which was to introduce health systems or models of developed countries into developing countries.  Health may be either Physical or mental,  Very often, Spiritual, Emotional and Financial health ay contribute and enrich the definition of health.  Physical, Genetic, Environmental and Socio-economic factors play decisive role on someone’s health,  Life style factors are also very pertinent one in the context of global health issue,  Preservation of good and sound health needs nutrition, physical activity, stress management , preventive care and social connection are very important issues,  Holistic and sustainable health are the call of the century.
DISEASE & HEALTH
DEFENCE MECHANISMS OF BODY  The environment surrounding us is crowded with organisms; not all of them are visible but some enter our body and cause harm, resulting in infection and disease.  There are numerous others that do not always cause disease even when they use the human body as a host, and instead establish beneficial relationships with the human host.  The organisms that get into the human body and do harm of some kind vary in magnitude from those visible to the naked eye like worms or helminthes, to ones largely visible only under microscopy including fungi, protozoa, bacteria and viruses, to others not seen like prions. Such organisms that are agents of disease are referred to as pathogens.  The human body has a range of defence mechanisms to tackle these pathogens. The first line of defence is the ability of the human host to prevent entry of the pathogen and the next response is that mediated by the host’s natural or innate immunity.  If the pathogen overcomes these obstacles, the host has the ability to resist infection and disease by resorting to adaptive immunity.
DEFENCE MECHANISMS OF BODY  Failure at any of these stages of the battle between the pathogen and the human host can result in disease and even death of the host.  The human immune system is complex and highly organized, and functions to protect the individual from a range of environmental agents or pathogens that can infect the body and cause disease.  From the perspective of this book it is important to note from the start that poor nutrition can compromise the body’s ability to mount effective defence and immune responses, while infections, in turn, can undermine the normal nutritional status of an individual.  From the above perspectives, human body exercises three basic defence mechanisms to get rid of from the diseases as follows- i. Physical barriers, ii. Defence cells and proteins, inflammation and fever, iii. The Immune system.
IMMUNITY-TYPES  IMMUNITY: i. Acquired Immunity- ii. Innate Immunity  ACQUIRED IMMUNITY  ACTIVE i. Natural--- Follows clinical or subclinical infection ii. Artificial---- Induced by Vaccination  PASSIVE  Natural--- Transplacental passage of IgG antibody protects child for first 6 moths of life  Artificial- Injection of preformed antibody (ATS) derived from serum or animals  INNATE  Species specific- Birds immune to tetanus,  Racial- Algerian sheep immune to anthrax,  Individual-Seen in endemic era.
IMMUNITY-TYPES
INNATE IMMUNITY  It is known as native immunity,  Resistance to infections with which a person or a lower animal is born,  It is attributed to the genetic and constitutional make-up,  Not affected by prior contact with microorganism or immunization,  It is non-specific,  Immunity persists throughout the whole life.  It is of three types at the level of species, race or individual- i. Species specific immunity-Physiological and biochemical differences responsible; B. anthracis infects human but not chicken, birds immune to tetanus. ii. Racial immunity-Within species, some are susceptible to infection but others are immune like Algerian race of sheep is immune to anthrax but is a common disease of other races of sheep, iii. Individual immunity- It is exhibited by different individuals ; some are highly susceptible while others are immune.
MECHANISM OF INNATE(NATURAL) IMMUNITY  Although, the different factors like age, hormonal influence and nutrition contribute a lot in the domain of innate immunity.  MECHANISM OF INNATE IMMUNITY  Three components play crucial role-  Physio -chemical barrier,  Humoral, Cellular Inflammatory response  Physiochemical barrier:  It consists of epithelial surface and cilia as physical barrier and different bactericidal secretions included collectively build up this system.  Skin-  The sebaceous secretions containing saturated and unsaturated fatty confer protection against bacteria and fungi,  The relatively dry skin with high salt concentrations in drying sweat are lethal to bacteria and fungi,  It offers primary defence mechanisms against infections.
MECHANISM OF INNATE IMMUNITY  Nose, Nasopharynx and Respiratory tract:  The inhaled bacteria arrested in the tortuous nasal passages on the moist surface,  The inspired air is largely freed of bacteria in the upper respiratory passage and that pass beyond the larynx are trapped in the bronchial mucosa ,  The sticky respiratory mucosa and hair like cilia sweeps the secretion and is swallowed or coughed out by cough reflex,  Small particulate materials manage to reach out alveoli are ingested by phagocyte cells,  The nasal and respiratory secretions contain mucopolysacharides that can neutralize influenza virus and some other viruses,  Any kind of defect and damage in the function of respiratory tract makes the lungs vulnerable to infections,  This confers first line defence mechanisms operated to resist infection.
MECHANISM OF INNATE IMMUNITY  Mouth, stomach and intestinal tract:  Saliva possesses mild bactericidal action,  The anaerobic colon bacteria produce fatty acids in contact to the bactericidal action- colonization resistance refers to resistance offered by the predominant normal flora to infection,  The high acidity of the stomach always destroyed most ingested bacteria from the diverse sources,  In addition to that, the large intestinal tract offers a resistance mechanism against the microbial infection.  Conjunctive  The lachrymal glands excitation triggers the production of mild saline water,  It also contains lysosomes having bactericidal action,  All these offers a strong conjunctive secretions to offer protection against microbes supposed to enter through eyes.
MECHANISM OF INNATE IMMUNITY  The genitourinary tract:  The urine generally slightly acidic; the flushing action of urine maintains sterility of both male and female urethra,  Semen contains spermine and zinc having antibacterial activity,  The acid reaction of the vaginal secretion in female due to fermentation of glycogen in the epithelial cells by the resident acidic flora possess markedly bactericidal action towards the microbes supposed to cause genitourinary damages in the human,  This line of system enables the body not to enter pathogens through genital and urinary apertures.  B. CELLULAR AND HUMORAL BARRIERS  Phagocytes accumulates at the site of infection along with outpouring of natural and antibacterial substances and deposition of fibrin,  Fibrin acts as net not to allow the microbes to spread further infection,  It may be of the following types-
CELLULAR AND HUMORAL BARRIERS  NEUTROPHIL POLYMORPH NUCLEAR LEUCOCYTES:  Short lived cells formed by bone-marrow and circulate in the blood stream for about 6-7 hours,  Polymorphs reaches o the site of infection attracted by the chemotactic substances,  Phagocytosis is promoted in the presence of specific antibody and complement,  MACROPHAGES  These are mononuclear phagocyte cells – of the reticulo endothelial system distributed throughout the body- both as wandering amoeboid cells (monocytes), fixed cells in tissue ( histocyctes) and reticulo endothelial cells in bone-marrow, spleen, liver, lymph node, thymus etc.  Phagocyte actions done by the following stages- i. Chemotaxis - Phagocytes reach to the site of infection, ii. Attachment- Infective agent adhere to phagocyte, iii. Ingestion- By means of phagosome, phagocyte cells engulf the material and by hydrolytic enzymes, phagolysosome destroy them.
CELLULAR AND HUMORAL BARRIERS
CELLULAR AND HUMORAL BARRIERS  NATURAL KILLER CELLS (NK CELLS)  A class of lymphocytes called natural killer cells (NK) play the role in non-specific defence against viral infections and tumors,  NK cells selectively kill the selectively virus-infected cells and tumor cells by means of interferon.  HUMORAL FACTORS  These are associated with nonspecific antibacterial substances in blood and tissues,  It may be of the following types-  Properdin – Present in blood serum, causes lyses of Gram-negative bacteria with the help of Mg+ and complement, inactivate some viruses,  Complement- Non-specific, acts on microorganism sensitized by specific antibody with bactericidal activity,  Lysozyme- Bactericidal enzyme of low molecular weight basic protein present in polymorph nuclear leucocytes, tears and other bodies, lyses the mucopeptide of many Gram (-) bacteria,  Acute phase proteins- Increase in concentration during acute inflammatory responses , like C-reactive protein (CRP), play defensive role of body by enhancing host resistance.
CELLULAR AND HUMORAL BARRIERS  INFLAMMATION  During the infection , the host protection mechanism operated,  The blood vessels particularly arterioles constrict initially and dilate leading to the increased blood flow,  The blood flow slows down and margination of leucocytes,  The leucocytes escape from the blood vessels by diapedesis and attracted by the chemotaxis process as released by the microorganism, Due to the large number of leucocytes, there is an outpouring of plasma at the site of injury,  These dilute the toxic substances, hence the infection site trigger the defence mechanisms.  FEVER  A slight raise of temperature accompanies with infection,  It is caused by Interleukin I (IL1) or IL6 and tumor necrosis factor (TNF) that can act on hypothalamus,  Host immune mechanisms trigger due to increase of body temperature.
ACQUIRED IMMUNITY  Resistance against diseases acquired by an individual during the disease is called acquired immunity or specific immunity.  Acquired immunity of two types- Active and passive,  ACTIVE IMMUNITY  Resistance developed by an individual after effective contact with antigen either by the consequences of natural infection by the microbes or by means of vaccination as a part of preventive measures,  Immune system actively participates producing antibody and often cell mediated immunity also, It develops slowly over a period but persists for a long time usually from days to years.  MECHANISM  The body’s immune apparatus offers protection by synthesizing antibody either by Antibody immune system (AMIS) or cell mediated immune system (CMIS),  During the encounter between host and microbes, antibody formation starts only after a latent period , attributing to antigen to combine with pre-existing antibody in blood,  Lowering of blood concentration level of antigen ,  This is called primary immune response.
ACQUIRED IMMUNITY  After the first encounter, the same antigen when enters into body, the immune response becomes more rapid and stronger to resist the antigen , called secondary immune response.  HUMORAL OR ANTIBODY MEDIATED IMMUNE SYSTEM (AMIS)  It is a critical component of the adaptive immune system.  This specialized response relies on antibodies, which are proteins produced by B cells, to identify and neutralize pathogens such as bacteria, viruses, and toxins. Antibodies provide highly specific targeting, ensuring precision in neutralizing threats while minimizing harm to the body’s own cells.  Antibodies, or immunoglobulin, are Y-shaped proteins composed of variable and constant regions. The variable region, located at the tips of the "Y," is uniquely structured to bind to specific antigens, much like a lock and key.  The constant region determines the antibody's functional properties, such as its ability to recruit other immune components.
ACQUIRED IMMUNITY  Antibodies exert their effects through three primary mechanisms:  Agglutination: agglutinate the antigens by special mechanisms,  Neutralization: Binding to pathogens or their toxins to prevent them from interacting with host cells.  Opsonization: Coating pathogens to enhance their recognition and engulfment by phagocytes.  Complement Activation: Triggering a cascade of proteins that help destroy pathogens and recruit immune cells.  STEPS:  When a B cell encounters an antigen, it processes and presents fragments of the antigen on its surface using major histo-compatibility complex (MHC) molecules.  T helper cells recognize this presentation and release signaling molecules (cytokines) that activate the B cell.  Once activated, B cells proliferate and differentiate into plasma cells, which secrete large quantities of antibodies specific to the encountered antigen. Some B cells become memory cells, providing long-lasting immunity by enabling a faster and stronger response upon re-exposure to the same pathogen.
ANTIBODY MEDIATED IMMUNE SYSTEM
ACQUIRED IMMUNITY  CELL MEDIATED IMMUNE SYSTEM ( CMIS)  It mainly depends on specifically developed T-cells by certain antigens,  The sensitized T-lymphocytes become active in operation to counter chronic infections,  Helper T cells are like the “managers” of the immune response. They secrete cytokines, which activate or control the activities of other lymphocytes. Most helper T cells die out once a pathogen has been cleared from the body, but a few remain as memory cells.  These memory cells are ready to produce large numbers of antigen- specific helper T cells like themselves if they are exposed to the same antigen in the future,  Cytotoxic T cells destroy virus-infected cells and some cancer cells. Once activated, a cytotoxic T cell divides rapidly and produces an “army” of cells identical to itself.  These cells travel throughout the body “searching” for more cells to destroy. cytotoxic T cell destroys a body cell infected with viruses.  This T cell releases toxins that form pores in the membrane of the infected cell. This causes the cell to burst, destroying both the cell and the viruses inside.
CELL MEDIATED IMMUNE RESPONSE
ACQUIRED IMMUNITY  IMMUNOLOGICAL MEMORY:  Besides development of antibody mediated immunity, active immunity is associated with immunological memory,  The immune system retains the memory of a prior antigenic exposure for long periods and are able to produce a secondary type of immune response when it encounters the same antigen once again,  The generation of memory T cells, long-lived cells that give an accelerated response to antigen, is much less well understood than the generation of effectors T cells .  TYPES OF ACTIVE IMMUNITY  Active Immunity of two types- Natural and artificial  NATURAL-  The subclinical infection after repeated exposure of small antigen generally develops this natural immunity by the means of natural discourse,  Such immunity is long lasting and plays role in epidemics like the poliomyelitis, TB etc.
ACQUIRED IMMUNITY  ARTIFICIALACTIVE IMMUNITY  It is generally done by vaccination by the introduction of live, attenuated or killed microorganism,  The materials derived from toxoids,  The most commonly toxoids are as follows- i. Live bacterial vaccines like BCG, anthrax, plague, brucella vaccines, ii. Killed bacterial vaccines like TAB for enteric fever, auto vaccine  Viral live vaccines like small pox, measles, influenza, mumps etc,  Killed viral vaccines like Salk vaccine for Polymelities,  Toxoids for tetanus and diphtheria.  Attenuation is a process to design vaccine by aging of culture , cultivation at high temperature through the passage of different animal species. The immunity derived by the use of live vaccine parallels to the natural infection through the immune response may be lower order.  Killed vaccines are the vaccines designed by the killing of organisms by heat, formalin, phenol, alcohol , U-V light and photodynamic inactivation.
ACQUIRED IMMUNITY  Toxoids are preparation of bacterial endotoxins inactivated by formalin (formal toxoid) or by alum (APT). They retain immunogenicity but lose toxigenicity.  PASSIVE IMMUNITY  The resistance is transmitted passively to a recipient by transfer of preformed antibodies against infective agent or toxin from another host,  The immune response plays no active role and the protective mechanisms comes from readymade antibodies prepared earlier,  It is short lasting, only for a days to week,  Useful when instant immunity is required,  It generates no immune memory,  Passive immunity of two types- Natural and Artificial.
ACQUIRED IMMUNITY  NATURAL PASSIVE IMMUNITY  Resistance passively transferred to fetus by mother,  Human colostrums contains high concentration of IgA antibodies , resistant to human intestinal digestion and offers protection to the neonate,  Infant acquires some degree of immunological independence by about three moths of age,  Maternal antibodies give passive protection against infectious diseases to the infant till three months of age,  Active immunization of pregnant mother , the quality of passive immunity in infants can improved , hence administration of tetanus toxoid in recommended during pregnancy.  ARTIFICAL PASSIVE IMMUNITY  Resistance passively transferred to a recipient to the parental administration of antibodies,  Passive immunization is done usually done in the treatment of some diseases associated to provide temporary immunity to individuals who have been exposed to infectious organism and who have not been actively immunized,
ACQUIRED IMMUNITY  Passive immunization is used in the treatment of some diseases associated with toxin like diphtheria, Snake and Spiders bite ,  It is used as a specific or nonspecific-immunosuppressant immunoglobine and antilymphocyte globulin respectively.  There are three types of iimmunoglobine preparations-  Pooled human serum globulin-  Prepared from plasma pools of healthy adults containing of high levels of antibodies against common infectious microorganisms prevalent in community,  Some available immunoglobulin preparations include tetanus, hepatitis B, diphtheria, botulism rabies and measles immunoglobulin,  Human Immunoglobulin (HLG)- Special immune serum globulin with a known content of antibody to specific agents like hepatitis B virus,  Animal antiserum -Antitoxic serum is administered by injection of toxoid into horses in increasing doses till the blood is rich in circulating antibodies,
ACQUIRED IMMUNITY  These antibodies may contain foreign protein and it may cause severe hypersensitivity reactions. After the first injection of foreign serum antibody, it is only eliminated by metabolic breakdown, But on the second encounter, it is eliminated much rapidly because it combines with antibodies to horse serum,  This is called immune elimination which limits the usefulness of repeated immunization.  Besides these immunity processes, the following types of immunity can be considered in this regard.  COMBINED IMMUNISATION  A combination of active and passive methods of immunization is used which is called combined immunization,  A partially immunized or never been immunized is used for the same,  Here, one should receive a dose of vaccine as well as human immunoglobulin(HIG) in separate arms,  For example, human tetanus immunoglobulin (TIG) injected in one arm and first dose of tetanus toxoid on the other.
DIFFERENCE BETWEEN ACTIVE IMMUNITY PASSIVE IMMUNITY Produced actively by the immune system of body, Receive passively by host. Induced by the infection by microbes or any immunogenic agents, Conferred by introduction of readymade antibodies. Immune response is durable and effective in true sense, Immune response short lived and less effective. Immunity develops only after lag period, Immunity becomes effectively after administration. Immunological memory is retained by the memory like T cells ; subsequent changes and fortification is done with booster dose, No immunological memory is developed. Subsequent administration of antibody is less effective. After antigenic stimulus negative phase may occur due to antigen combining with any preexisting antibody, No negative phase. Serve no purpose in immunodeficient host. Applicable to immunodeficient host.
SPECIAL TYPES OF IMMUNITY  ADAPTIVE IMMUNITY  Immunization by injection of immunologically competent lymphocytes is known as adaptive immunity,  It is induced by injection of immunologically competent lymphocytes and the extract is known as ‘transfer factor’,  Such type of immunization is done in the treatment of certain types of diseases like lepromatous leprosy.  HERD IMMUNITY  Collective resistance of disease by the community in the environmental setting,  After successful vaccination programme in large scale, the decreasing persons of susceptible persons of infection may cause the reduction of possibility of the rest of unvaccinated population ,  This indirect unvaccinated (non-immune) individuals develop this type of special immunity is called herd immunity.
THANKS FOR YOUR VISIT  ACKNOWLEDGEMENTS: a. Google for images, b. Different websites for enriching the course content, c. Science Direct pages, d. A Textbook of Microbiology- P. Chakraborty, e. Immunology, 5th edition- Benjamini, Coico & Sunshine f. Immunobiology – Janeway, g. Concept of Genetics- Klug. Cummings, Spencer, Palladino, DISCLAIMER:  This presentation has been designed to address the academic fraternity without any financial interest. This is absolutely free to use . The author does not claim any kind of financial benefits from this content.