INNATE VERSUS ADAPTIVE IMMUNITY Assist Prof Dr. Syed Yousaf Kazmi OBJECTIVES • Define and classify immunity • Distinguish innate and adaptive immunity • Explain the mechanism of innate and adaptive immunity • Discuss the clinical importance of immunity IMMUNITY DEFINITION “A state of having sufficient biological defenses to avoid infection, disease or other unwanted biological invasion” Capability of the body to resist harmful microbes from entering it CLASSIFICATION OF IMMUNITY A. INNATE Nonspecific host defense not acquired through contact with an antigen e.g. intact skin, mucous membranes etc. B. ADAPTIVE Protection acquired through natural or deliberate introduction of an antigen into a responsive host CLASSIFICATION OF IMMUNITY ADAPTIVE IMMUNITY 1. Natural If adaptive immunity is acquired through some natural processes e.g. infection a. Naturally acquired Active immunity When immunity is induced in the host by some natural means e.g. immunity after Hepatitis B infection b. Naturally acquired Passive immunity When immunity is passively transferred from an immune host e.g. maternal transfer of IgG against various infections CLASSIFICATION OF IMMUNITY ADAPTIVE IMMUNITY 2. Artificial Adaptive immunity acquired through intervention a. Artificially acquired active immunity Immunity acquired post vaccination b. Artificially acquired passive immunity Immunity acquired from administration of preformed antibodies against specific disease e.g. Rabies immunoglobulins CLASSIFICATION OF IMMUNITY CLASSIFICATION OF IMMUNITY ADAPTIVE IMMUNITY Can also be classified as 1. Humoral immunity Immunity that is mediated by secreted antibodies 2. Cell mediated immunity The protection provided by T-lymphocytes alone INNATE & ADAPTIVE IMMUNITY INNATE IMMUNITY – Resistance that exists prior to exposure to the microbe – Readily available – Non specific – Does not improve on repeated exposures – There is no immunologic memory – e.g. Natural barriers like skin, stomach acid ADAPTIVE IMMUNITY – Immunity that is developed on exposure of antigen – Develops in few days – It is highly specific – It improves on repeated exposure – There is immunologic memory – e.g Immunoglobulins, sensitized T lymphocytes MECHANISMS OF INNATE IMMUNITY INNATE IMMUNITY A. Factors that limit entry of microorganisms into the body Keratin layer of intact skin Acts as mechanical barrier Lysozyme in tears and other secretions Degrades peptidoglycan in bacteria cell wall Respiratory cilia Elevate mucus-containing trapped organisms Low pH in stomach and vagina; fatty acids in skin Retards growth of microbes Surface phagocytes (e.g., alveolar macrophages) Ingest and destroy microbes Defensins (cationic peptides) Create pores in microbial membrane Normal flora of throat, colon, Occupy receptors, which prevents colonization by and vagina pathogens MECHANISMS OF INNATE IMMUNITY B. Factors that limit entry of microorganisms into the body Natural killer cells Kill virus-infected cells Neutrophils Ingest and destroy microbes Macrophages and dendritic cells Ingest and destroy microbes, and present antigen to helper T cells Interferons Inhibit viral replication Complement (Alternate pathway) C3b is an opsonin; membrane attack complex creates holes in bacterial membranes Transferrin and lactoferrin Sequester iron required for bacterial growth Fever Elevated temperature retards bacterial growth Inflammatory response Limits spread of microbes MECHANISMS OF ADAPTIVE IMMUNITY • Can be antibody-mediated (humoral), cell-mediated (cellular), or both • Microbe e.g. bacteria is taken up by Antigen presenting Cell (Macrophage, Dendritic Cell) • Nonself antigens reappear on the APC surface with proteins encoded by the major histocompatibility complex (MHC) • Presented to clones of T lymphocytes • The MHC-antigen complexes are recognized by specific receptors on the surface of T cells • Variety of cytokines that induce lymphocyte proliferation MECHANISMS OF ADAPTIVE IMMUNITY Antibody-mediated arm • Helper (CD4) T lymphocytes recognize the antigens complexed with class II MHC proteins • produce cytokines that activate B cells expressing antibodies • B cells undergo clonal proliferationdifferentiate to form plasma cellsAntibodies • neutralization of toxins and viruses and opsonization (coating) of the pathogen MECHANISMS OF ADAPTIVE IMMUNITY Cell-mediated arm • Antigen-MHC class II complex is recognized by helper (CD4) T lymphocytes • T cells produces cytokines, becomes activated, and expands by clonal proliferation Humoral & Cell Mediated Arms Antibody-mediated arm of Adaptive Immunity CLINICAL IMPORTANCE OF IMMUNITY Intact and functioning immune system is essential for health In immune disturbances, following conditions may arise a. IMMUNODEFICIENCY CONDITIONS e.g. HIV inf, other immune def conditions b. HYPERSENSITIVITY REACTIONS e.g. Asthma, Hay fever etc c. AUTOIMMUNE DISORDERS e.g. Rheumatiod arthritis, SLE etc.