Chapter 67

1. Chapter 67 Review of the Immune System

2. Review of the Immune System • Two types of immune responses • Natural immunity (innate) • Specific acquired immunity • Cell-mediated • Antibody-mediated: humoral

3. Immune System: Cells • B lymphocytes (B cells) • Make antibodies • Cytolytic T lymphocytes • Cytolytic T cells, CD8 cells • Do not produce antibodies • Attack and kill target cells directly • Helper T lymphocytes • Helper T cells, CD4 cells • Antibody production by B cells • Promote delayed-type hypersensitivity (DTH) • Activation of cytolytic T cells

4. Immune System: Cells • Helper T lymphocytes • Helper T cells, CD4 cells • Required for an effective immune response • Antibody production by B cells • Promote DTH • Activation of cytolytic T cells

5. Immune System: Cells • Macrophages • Begin in bone marrow, enter blood as monocytes, and infiltrate tissues, where they evolve into macrophages • Principal scavengers of the body • Specific acquired immunity • Activation of T cells • Final mediators of DTH • Phagocytize cells tagged with antibodies • Also play key roles in natural immunity and inflammation

6. Fig. 67–1. Maturation of blood cells.

7. Immune System: Cells • Dendritic cells • Mast cells and basophils • Mediate immediate hypersensitivity reactions • Neutrophils (polymorphonuclear leukocytes) • Phagocytize bacteria and other foreign particles • Eosinophils • Attack and destroy foreign particles that have been coated with antibodies of the immunoglobulin (Ig)E class

8. Antibodies • Alternative names • Immunoglobulins • Gamma globulins • Family of structurally related glycoproteins • Mediate humoral immunity • Recognize and bind with specific antigens • Produced by B lymphocytes • Five classes of antibodies • IgA, IgD, IgE, IgG, and IgM

9. Fig. 67–2. Antibody structure.

10. Antigens • Molecules that induce specific immune responses • May trigger production of antibodies or cytotoxic T cells, or both • Antibodies recognize and bind selected small portions of the antigen • More than one antibody can bind to the antigen

11. Fig. 67–3. Memory and time limitation of immune responses.

12. Characteristic Features of the Immune Response • Specificity • Immune responses are triggered by specific antigens • Diversity • Millions of different antigenic determinants • Memory • Exposure to an antigen affects the immune system such that re-exposure produces a faster, larger, and more prolonged response • Time limitation • Selectivity for antigens of nonself origin • Targets only foreign antigens (normal conditions)

13. Phases of the Immune Response • Recognition phase • Antigen recognition by B cells and T cells • Activation phase • Proliferation • Differentiation of activated lymphocytes • Effector phase • Elimination of antigen

14. Antibody-Mediated (Humoral) Immunity • Production of antibodies • Interaction of three types of cells • B cells • Make antibodies • Helper T cells (CD4 cells) • Stimulate B cells • Antigen-presenting cells (macrophage or dendritic) • Activate CD4 cells

15. Antibody-Mediated (Humoral) Immunity • Antibody effector mechanisms • Opsonization of bacteria • Activation of the complement system • Neutralization of viruses and bacterial toxins

16. Fig. 67–4. Major events in antibody-mediated (humoral) immunity.

17. Cell-Mediated Immunity • Two branches • Delayed-type hypersensitivity (DTH) • Activation of helper T cells • Activation of macrophages • Cytolytic T lymphocytes (CTLs, CD8 cells) • Activation of cytolytic T cells • Recognition of virally infected target cells • Mechanism of cell kill • Binding of a CTL to its target cell • Release of mediators that kill the target • Cause target cell lysis

18. Fig. 67–5. Cell-mediated immunity: delayed-type hypersensitivity.

19. Fig. 67–6. Cell-mediated immunity: cytolytic T cells.