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PROTECTIVE IMMUNITY TO MICROBES

PROTECTIVE IMMUNITY TO MICROBES. By. Dr. Emad AbdElhameed Morad. Lecturer of Medical Microbiology and Immunology. IMMUNITY TO EXTRACELLULAR BACTERIA. (Innate immunity) Complement activation (alternative and lectin pathways). Phagocytosis Inflammation. (acquired immunity)

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PROTECTIVE IMMUNITY TO MICROBES

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  1. PROTECTIVE IMMUNITY TO MICROBES By Dr. Emad AbdElhameed Morad Lecturer of Medical Microbiology and Immunology

  2. IMMUNITY TO EXTRACELLULAR BACTERIA Dr. Emad AbdElhameed Morad

  3. (Innate immunity) • Complement activation (alternative and lectin pathways). • Phagocytosis • Inflammation Dr. Emad AbdElhameed Morad

  4. (acquired immunity) • It is mediated mainly by humoral immunity (antibodies) through: • Toxin neutralization (e.g., diphtheria) • Inhibition of bacterial adherence to target cells (e.g., IgA on mucosa) • Complement activation • Opsonization (by IgG) • Bacterial agglutination Dr. Emad AbdElhameed Morad

  5. IMMUNITY TO INTRACELLULAR BACTERIA Dr. Emad AbdElhameed Morad

  6. Examples of intracellular bacteria are tuberculosis, leprosy, listeria. (Innate immunity) • Natural killer cells kill the infected cells. Dr. Emad AbdElhameed Morad

  7. (acquired immunity) • It is mediated mainly by cell mediated immunity through: • Destruction of infected cells through T cytotoxic cells. • Natural killer cells become also activated. • Macrophages become activated by IFN γ. Dr. Emad AbdElhameed Morad

  8. IMMUNITY TO FUNGI Dr. Emad AbdElhameed Morad

  9. Protective responses consist mainly of innate immunity mediated by phagocytes (neutrophils & macrophages). • So, neutropenic patients are very susceptible to fungal infection. • As for acquired immunity, CMI plays the main role. Dr. Emad AbdElhameed Morad

  10. IMMUNITY TO VIRUSES Dr. Emad AbdElhameed Morad

  11. (Innate immunity) • Natural killer cells. • Type I interferon (IFN α and IFNβ) Dr. Emad AbdElhameed Morad

  12. Type I interferons are produced early after viral infection before the appearance of antibodies. • They inhibit intracellular replication of viruses in nearby cells by inducing proteins that prevent translation of viral mRNA. • IFN activity is not specific. That means interferon induced by one virus can inhibit replication of any other virus. • IFN activity is species specific. That means, an interferon produced in mice will only be active in mice. • So, it is produced by gene cloning. Dr. Emad AbdElhameed Morad

  13. (acquired immunity) • Antibody mediated mechanisms: • Virus neutralization. • Antibodies may stabilize viral capsid and prevent release of viral genome. • Destruction of free virus particles by complement activation & opsonization. Dr. Emad AbdElhameed Morad

  14. VIRUS NEUTRALIZATION Dr. Emad AbdElhameed Morad

  15. Antibodies can neutralize virus infectivity by preventing its attachment to receptor sites on susceptible cells. • IgG and IgM neutralize viruses which pass through the blood stream causing viremia before they reach target organs as in measles, mumps, polio, • So in these diseases, one attack is followed by long lasting immunity. • The situation is completely different with viruses which cause superficial non viraemic infections as influenza and common cold where the target tissue is respiratory mucosa. Dr. Emad AbdElhameed Morad

  16. IgA neutralize virus infectivity at the mucous surfaces. • So in these diseases, one may get several attacks during the same season due to: 1- Weak immunity involved. 2- Presence of several antigenic types. 3- Emergence of antigenic variants. Dr. Emad AbdElhameed Morad

  17. (acquired immunity) • Cell mediated mechanisms: *TH1 cells secrete the following cytokines: • IL2 which activates T cytotoxic cells that kill virus infected cells by secreting perforins & granzymes and induction of apoptosis. • NK cells are also activated by IL 2 and kill virus infected cells but without MHC restriction. Dr. Emad AbdElhameed Morad

  18. IFN γ which causes activation and recruitment of macrophages. • Antibody depenedent cellular cytotoxicity (ADCC). • It occurs when specific antibody coat virus infected cells. NK cells, macrophages and neutrophils will then kill the infected cells. Dr. Emad AbdElhameed Morad

  19. (Antibody dependent cellular cytotoixity) Virus infected cell Lysis of the infected cell Dr. Emad AbdElhameed Morad

  20. Thank You Dr. Emad AbdElhameed Morad

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