Chapter 43 – The Body’s Defenses

1. Chapter 43 – The Body’s Defenses

2. Vertebrate lines of defense • Innate immunity – broad defense • Acquired Immunity – specific defense

3. Innate – Phagocytic Cells • Phagocytosis: the ingestion of invading microorgansims by certain types of white blood cells (phagocytes) • Neutrophils: most abundant, function work inside tissues, self destruct during phagocytosis • Macrophages: large, long lived, work inside tissues, permanently found in spleen and lymph tissue, • Eosinophils: defense against multicellular parasitic invaders, secrete enzymes that damage invader

4. Innate – antimicrobial proteins • Interferons: provide defense against viral infections • Secreted by viral infected cells which stimulate other cells also produce interferons – shut down viral replication • Multiple types: (α, β and γ) but not virus specific

5. Inflammatory response • Tissue injury, trigger mast cells to release chemical signals (histamine) that cause capillaries to dilate and increase permeability • Antimicrobial proteins and clotting elements are delivered to the injured area • Release chemokines (small proteins), direct migration of phagocytes to injured area • Phagocytes remove pathogens allowing tissue healing

6. Innate – NK cells • Natural Killer (NK) cells – patrol body attacking virus-infected body cells and cancer cells • Releases a chemical to trigger apoptosis or programmed cell death

7. Acquired - lymphocytes • B cells and T cells: circulate the blood and lymph, concentrated in spleen and lymph tissue, recognize antigens with specific receptor proteins • Both originate from pluripotent stem cells in bone marrow but T cells finish development in the thymus gland • Antigen: any foreign molecule that is specifically recognized by a lymphocyte

8. Clonal Selection • Antigens bind to specific receptors, activates a small/specific fraction of lymphocytes, will give rise to thousands of clone cells to eliminate the antigen • Effector cells: short-lived cells that combat the antigen • Memory cells: long-lived cells that bear receptors for the antigen

9. Clonal Selection

10. Overview of acquired immune response • 2 branches • Humoral immune response – activation and clonal selection of B cells, results in production of antibodies in blood and lymph • Cell mediated immune reponse – activation and clonal selection of cytotoxic T cells, directly destroy target cells • Helper T cells: respond to nearly all antigens, when activated secrete cytokines that stimulate lymphocytes, promote both humoral and cell mediated responses (figure 43.15) • Cytotoxic T cells: eliminate body cells infected by viruses and other intracellular pathogens as well as cancer cells and transplanted cells (figure 43.16) • B cells: antigen/antibody interaction to proteins and polysaccharides on the surface of cells (figure 43.17)

12. Helper T Cells

13. Cytoxic T Cells

14. B Cells

15. Classes of Antibodies • Classes of Antibodies • Ig stands for immuno-globulin (another name for antibody)

16. Antibody-Mediated Disposal of Antigens • Phagocytosis • Viral neutralization: binding of antibodies to viral surface proteins, blocks binding to host and increases phagocytosis • Agglutination of antigen-bearing particles • Precipitation of soluble antigens: aggregates of body fluid dissolved antigens • Cell Lysis • Membrane attack complex (MAC): forms a pore in cell surface, ions and water rush in, causing cell to lyse

17. Antibody-Mediated Disposal of Antigens

18. Antibodies

19. Immunity – health and disease • Immunizations • Active immunity (vaccination): depends on person’s own lymphocytes • Passive immunity: transferring antibodies from someone who is immune to someone who is not, lasts only as long as antibodies last

20. Immune system problems • Allergies: exaggerated responses to antigens called allergens; allergen binding to mast cells causes histamine releases, causes vascular system changes leading to allergy symptoms, take antihistamines to reduce symptoms

21. Immune system problems • Autoimmune diseases: where the body turns on its own cells • Rheumatoid arthritis • Multiple sclerosis • Immunodeficiency diseases: can be inborn (SCIDS) or acquired (AIDS)