The document summarizes the immune system's defenses against various pathogens. It describes both innate and acquired immunity. The innate immune system provides non-specific defenses like physical barriers, chemicals, and phagocytosis. The acquired immune system mounts pathogen-specific responses through antibodies, B cells, T cells, and cytokines. Together these defenses protect the body from bacteria, viruses, and parasites through mechanisms like inflammation, phagocytosis, and cell-mediated or antibody-mediated immunity.

4. Immune System Functions: Overview of Defenses Figure 24-1: Viruses

11. PRO-INFLAMMATORY CYTOKINES

12. Components of the Immune System Bacteria Entering B Cells T Cells Macrophage

13. The Innate Immune System Bacteria Entering NK Cells Phagocytosis Chemotaxis Virus Infected Cell Lysis

14. Innate and Adaptive Immune Responses Lysis Antibodies Plasma Cell Memory B cells Helper B Helper T Memory T cell Cytotoxic T cell Suppressor T cell Bacteria Entering Phagocytosis Chemotaxis Opsonization Antigen Presentation Virus infected cell

16. Lymphatic System: Overview of Immune Defense Organs & Cells Figure 24-2 ab: Anatomy of the immune system

18. Key Cells & Overview of their Function in Immune Defense Figure 24-4: Cells of the immune system

20. Innate Immunity: Phagocytosis & Inflammation Figure 24-6: Phagocytosis

22. Inflammatory Response: Cytokines Signal Initiation Figure 24-8: Membrane attack complex

24. Acquired Immunity: Antigen-Specific Responses Figure 24-13: Functions of antibodies

26. T Lymphocytes: Cell Mediated Immunity Figure 24-16: T lymphocytes and NK cells

28. Defenses against Bacteria: Complement P Activates Figure 24-17: Immune responses to bacteria

30. Viral Defense: Summary of Innate & Acquired Responses Figure 24-18: Immune responses to viruses

33. Viruses NNatural Immunity Virus infection directly induce the production of IFN, which inhibit viral replication and the expression of MHC molecules NK cells lyse virally infected cells. IFN enhance the activity of NK. TThus NK is the primary natural immune response to viral infection. Acquired Immunity Ab are important during early viral infection. Ab prevents entry to the host cells and opsonize viral particle for phagocytosis. CTL is important for established infection. Both CD4 and CD8 CTLs participate.

34. Immunity to Extracellular Bacteria Live in tissue space and induce inflammation and tissue destruction Release toxins: Endotoxin: bacteria cell wall components Exotoxin: secreted by bacteria. Toxins induce cell activation and modulate activities of kinases and other enzymes. Immunity to extracellular bacteria is aimed to eliminate the bacteria and neutralizing toxins. Natural Immunity: Phagocytes  Complement via the alternative pathway: C3b opsonize bacteria, C9 lyse bacteria and other by-products promote inflammation. Toxins could lead to the production of cytokins. Uncontrolled cytokine production could result in septic shock. Example: LPS activate macrophages to produce TNF Adoptive Immunity Humoral immunity is the principal protective mechanism IgG opsonize bacteria by binding to FcR on phagocytes. IgG and IgM neutralizing bacteria and prevent binding to cells Activate the complement system. C3b promotes phocytosis activity. CD4 T cells help antibody production and produce cytokines to help phagocytosis. Some Toxin can be superantigens.

35. Intracellular Bacteria Natural Immunity Can survive with in phagocytes due to the ability to interfere with lysosome movement. Natural immunity are quite ineffective. Difficult to eradicate and could cause chronic infections NK cells are the main force against intracellular infection. Acquired Immunity Mainly CMI. Type I CD4 cells activated by released antigens will produce IFNgamma which activate macrophages (RO) to effectively kill. CD4 cells also help CD8 cells to kill.  Activated macrophages during DTH cause tissue injury. Chronic antigen stimulation leading to granulomas, the histological hallmark. Granulomas limit spread but also cause tissue function impairment.

36. PParasites Parasites often have many stages. Some of the stage are in intermediate hosts. Natural Immunity Not effective  Whenever enter tissue or blood, parasite could survive and replicate. Complements are ineffective. Phagocytes could be replication factory. Acquires Immunity Diverse response to various parasites IgE and eosonophil are important for helminth infections. Driven by IL-4 and IL5. Eosinophil granules are toxic to helminthes. Granuloma formation to contain parasites and eggs. Intracellular parasite stimulate CTL.