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1. Immunology

1. Immunology. By. Dr. Emad AbdElhameed Morad. Lecturer of Medical Microbiology and Immunology. The immune system is divided into two divisions: Innate immune system Acquired (adaptive) immune system which has two mechanisms: Humoral immunity. Cell mediated immunity.

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1. Immunology

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  1. 1. Immunology By Dr. Emad AbdElhameed Morad Lecturer of Medical Microbiology and Immunology

  2. The immune system is divided into two divisions: • Innate immune system • Acquired (adaptive) immune system which has two mechanisms: • Humoral immunity. • Cell mediated immunity. • Innate immunity acts as a first line of defense against microbes. If these innate defenses fail, the acquired immunity is called upon.

  3. Host defense against extracellular microbes is mediated by humoral immunity. • When the microbe invades the host cell, the cell mediated immunity will take action.

  4. CELL MEDIATED IMMUNITY

  5. Cell mediated immunity plays a role in: • Resistance to intracellular infections such as viral infections. • Resistance to fungi & protozoa. • Resistance to tumors.

  6. Phases of cell mediated immunity: • Antigen processing and presentation. • Activation of CD4 T helper lymphocytes. • Activation of CD8 T cytotoxic cells. • Activation of macrophages.

  7. Antigen processing and presentation • Exogenous proteinsare ingested then digested by antigen presenting cell (APC) such as macrophage into smaller peptides. Then peptides will bind with MHC class IIwhich is transported to the surface of APC to be presented to CD4 T helper cells. • Endogenous proteinssuch as viral proteins on the other hand are processed then bind with MHC class I which is transported to the surface of APC to be presented to CD8 T cytotoxic cells.

  8. Activation of CD4 T helper lymphocytes • Two signals are required for activation of T helper lymphocytes: • The first signal is: • Recognition of peptide MHC class II complex on APC by T cell receptor of T helper cells. • The second signal is: • (Interleukin 1) IL 1 which is produced from APC. • IL 2 produced from T helper cells that will auto-activate themselves.

  9. The two previously mentioned signals will activate CD4 T helper cells. • Activated T helper (TH0) cells will become either TH1 or TH2 cells. • Some of activated T helper cells become memory cells to provide secondary immune response.

  10. TH1 cells will control cell mediated immunity by secreting: • Interleukin 2 (IL 2) which activates: • CD8 cytotoxic T lymphocytes. • Natural killer cells (NK cells). • Gamma interferon (IFN- γ ) which causes: • Activation and recruitment of macrophages. • TH2 cells will control humoral immunity by stimulating B lymphocytes.

  11. Activation of CD8 T cytotoxic lymphocytes • Two signals are required for activation of CD8 T lymphocytes: • The first signal is: • Recognition of peptide MHC class I complex on APC by T cell receptor of CD8 cytotoxic T lymphocytes. • The second signal is: • IL 2 produced from TH1 cells.

  12. Cytotoxic T lymphocytes will kill the target cells (example, virus infected cells) by: • Secretion of perforins and granzymes.Perforins create pores in the cell wall of the target cells through which granzymes enter the target cells causing their destruction. • Cytotoxic T lymphocytes express Fas ligand (Fas L) which binds to Fas on the target cells. The result is degradation of target cell DNA.

  13. Activation of macrophages • Macrophages are activated by IFN- γ secreted from TH1 cells. • Macrophages will infiltrate the site of infection and destroy the infected cells.

  14. BEST WISHES

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