The Immune System
39.1 Innate Defenses Are Nonspecific and Act Early
1. All animals have immunity, which is based on the ability to distinguish self from nonself antigens.
2. All animals have innate immunity, but vertebrates alone have acquired immunity.
3. Invertebrates’ innate immunity involves phagocytes and antimicrobial peptides.
39.2 Innate Defenses Are Nonspecific and Act Early
4. Skin, mucous membranes, tears, earwax, and cilia block pathogens.
5. Phagocytes and antimicrobial substances take part in inflammation, which is an immediate reaction to injury.
6. Complement proteins interact in a cascade that bursts bacterial cells.
7. Collectins are proteins that protect against pathogenic bacteria, viruses, and yeasts.
39.3 Acquired Defenses Are Specific and Act Later
8. Macrophages are antigen-presenting cells, engulfing, processing, and displaying foreign antigens held in place by major histocompatibility complex molecules.
9. A helper T cell binding to the antigen-presenting cell triggers the acquired immune response.
10. B cells, when activated by helper T cells, proliferate and differentiate into plasma cells, which secrete antibodies, and memory B cells.
11. An antibody is a Y-shaped protein composed of two heavy chains and two light chains. Each chain has a constant amino acid sequence and a variable sequence. The tips form an antigen binding site. Antibodies bind antigens and form complexes that attract other immune system components. Antibody molecules are incredibly diverse because DNA segments shuffle during early B cell development. This is the humoral immune response.
12. T cells carry out the cellular immune response. They are educated in the thymus gland to recognize self. Helper T cells activate other T cells and B cells. Cytotoxic T cells release biochemicals that bore into bacteria, kill them, and also destroy cells infected with viruses. T cells secrete cytokines, which control communication within the immune system.
13. Gamma-delta T cells coordinate responses of innate and acquired immunity. 39.4 The Human Immune System Throughout Life
14. Fetal T cells are “educated” in the thymus to recognize self.
15. A pregnant woman’s immune system dampens to accept the fetus, but fetal cells in her bloodstream can cause problems.
16. A baby gets antibodies from the mother, which is passive immunity, then begins to make its own. Immune function begins to wane in early adulthood.
39.5 The Unhealthy Immune System
17. HIV enters helper T cells and uses them to reproduce, killing them directly. The virus activates apoptosis in cytotoxic T cells.
18. Immune deficiency can be inherited, and some types are treatable with gene therapy.
19. Autoimmunity results when the immune system produces autoantibodies, which attack the body’s tissues.
20. Superantigens are foreign antigens that are displayed abnormally prominently on macrophages, activating many T cells that flood the body with cytokines, which cause symptoms.
21. An allergy is an immune reaction to a harmless substance. An allergen activates IgE antibodies, which cause mast cells to release allergy mediators.