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The Concept of Immunity

The Concept of Immunity. Immunity : Latin immunis , exempt Susceptibility : Lack of resistance to a disease, also known as Vulnerability Innate immunity : Inborn Adaptive immunity : Acquired, resistance to a specific pathogen. An Overview of the Body’s Defenses.

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The Concept of Immunity

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  1. The Concept of Immunity • Immunity: Latin immunis, exempt • Susceptibility: Lack of resistance to a disease, also known as Vulnerability • Innate immunity: Inborn • Adaptive immunity: Acquired, resistance to a specific pathogen

  2. An Overview of the Body’s Defenses ANIMATION Host Defenses: The Big Picture Figure 16.1

  3. First Line of Defense: I. Skin & Mucous Membranes • Skin • Keratin, a protective protein • Mucous membranes • Hairs • Cilia • Tears, Saliva, Urine, Vaginal secretions • Lysozyme

  4. Ciliary Escalator Figure 24.7

  5. II. Normal Microbiota • Normal microbiota compete with pathogens for nutrients • Keep pH unfavorable for disease microbes

  6. Second Line of DefenseI. Blood components

  7. Differential White Cell Count • Percentage of each type of white cell in a sample of 100 white blood cells • Early and late in infection: Neutrophil then Macrophage

  8. II. Lymphatic SystemTissue + Fluid Figure 16.5a

  9. III. Phagocytosis • Neutrophils • Macrophage • Presents Ag • Secret cytokines (lymphokines + interleukins) Figure 16.6

  10. IV. Inflammation • Releasing histamine • Vasodilation (histamine, kinins, prostaglandins, and leukotrienes) • Redness • Swelling • Pain • Heat • Tissue repair and wall-off

  11. Fever • Abnormally high body temperature • Body’s defensive mechanism • Increase enzyme activity and cytokine activity • Increase blood flow • Some bacteria can not survive at higher temperature • Disadvantage: • Tachycardia • Acidosis • Dehydration • 44–46°C fatal

  12. V. Antimicrobial Substances • Complements C3a + C5a cause inflammation C5b + C6 + C7 + C8 + C9 cause cell lysis

  13. V. Antimicrobial Substances • Interferons • a- and b- interferon: Virus infected cells to produce AVPs • g- interferon: Neutrophils and macrophages • Limitations: • Side effects • Short lived • Only prevents, not stop viral synthesis • No effect on a number of cancers • Ion-binding Proteins • AMPs: Natural antibiotics

  14. Types of Adaptive Immunity • Naturally acquired active immunity • Resulting from infection • Naturally acquired passive immunity • Transplacental or via colostrum • Artificially acquired active immunity • Injection of Ag (vaccination) • Artificially acquired passive immunity • Injection of Ab

  15. Dual Nature of Adaptive Immunity Figure 17.8

  16. Dual Nature of Adaptive Immunity • Humoral immunity: • B-cells • Ag-Ab • Cellular immunity • T-cells • Cytokines ANIMATION Humoral Immunity: Overview

  17. I. Antigens • It has to be large • Ag determinants = epitopes • Haptenand Carrier

  18. Antigens Figure 17.1

  19. Haptens Figure 17.2

  20. II. Antibodies • They are immunoglobulins (Ig) • The antigen-binding sitesrecognize epitope and determine valence • Constant Region / Variable Region • Heavy Chain / Light Chain

  21. Antibodies Figure 17.3a,b

  22. IgG Antibodies • Monomer • Most common and abundant (80%) • Fix complement • Cross placenta • Enhance phagocytosis; neutralize toxins and viruses; protects fetus and newborn • Half-life = 23 days

  23. IgM Antibodies • Pentamer • Agglutination • Fix complement • Agglutinates microbes; first Ab produced in response to infection • Half-life = 5 days

  24. IgA Antibodies • Dimer • 10–15% of serum Abs • In secretions • Mucosal protection • Half-life = 6 days

  25. IgD Antibodies • Monomer • In blood, in lymph, and on B cells • On B cells, initiate immune response • Half-life = 3 days

  26. IgE Antibodies • Monomer • Allergic reactions; lysis of parasitic worms • Half-life = 2 days

  27. III. B Cells • Diversity • Self – non-self discrimination • Memory

  28. 1st exposure to Ag First Clones 2nd exposure to Ag

  29. T-independent Activation of B Cells Figure 17.6

  30. T-dependent Activation of B Cells Figure 17.4

  31. Clonal Selection ANIMATION Humoral Immunity: Clonal Selection and Expansion Figure 17.5

  32. Clonal deletion:eliminates harmful B cells

  33. Immune Responses to an Antigen Figure 17.16

  34. Immune Responses to an Antigen

  35. Monoclonal Ab Production

  36. The Results of Ag-Ab Binding Destroy Made unavailable Figure 17.7

  37. IV. Cellular Immunity • T cells mature in the thymus • Thymic selection eliminates many immature T cells • T cells respond to Ag by T-cell receptors (TCRs) • T cells require antigen-presenting cells (APCs)

  38. T Helper Cells • CD4+ or TH cells (When activated) • Produce cytokines • Help in B cell and Tc cell activation

  39. T Cytotoxic Cells • CD8+or TC cells • Target cells are self carrying endogenous antigens • Activated into cytotoxic T lymphocytes (CTLs) • CTL causes apoptosis

  40. T Cytotoxic Cells Figure 17.11

  41. T Regulatory Cells • Treg cells • CD4 and CD25 on surface • Suppress T cells against self

  42. Antigen-Presenting Cells • Digest antigen • Ag fragments on APC surface with MHC • B cells • Dendritic cells • Activated macrophages ANIMATION Antigen Processing and Presentation: MHC

  43. A Dendritic Cell Figure 17.13

  44. Activated Macrophages Figure 17.14

  45. Natural Killer (NK) Cells • Granular leukocytes destroy cells that don’t express MHC I • Kill virus-infected and tumor cells • Attack parasites

  46. Cells Communicate via Cytokines

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