Immunology -- Natural Defenses

1. Immunology-- Natural Defenses Mhairi Sutherland

2. Outline • Components of whole blood • Blood cells • Differentiation • Function • Immune system • Innate • Adaptive

3. Components of whole blood Serum vs. Plasma • Serum: cell-free liquid, minus the clotting factors • Plasma: cell-free liquid with clotting factors in solution (must use an anticoagulant)

4. Blood cells • Red blood cells • Chickens are nucleated; mammals are not nucleated. • White blood cells • Platelets

5. Blood cell differentiation

6. The distribution of lymphoid tissues in the body Lymphocytes arise in the stem cells in the bone marrow and then differentiate in the bone marrow (B cells) or thymus (T cells). T and B cells migrate via the peripheral blood to the peripheral/secondary lymphoid organs: lymph nodes, spleen, addendix, Peyer’s patch etc. Lymphocytes become activated by antigen in these secondary lymphoid tissues (and lymphocytes will recirculate between the blood and these organs until they encounter antigen) The afferent lymphatic vessels carry APC cells from infected tissues to the lymph nodes where they activate T cells Activated T cells (after they have undergone proliferation and differentiation) leave via the efferent lymphatic vessels

7. White blood cells (leukocytes) • Granulocytes • Neutrophils • Eosinophils • Basophils • Lymphocytes • B cells • T cells (many types) • NK cells • Monocytes/Macrophages • Dendritic cells

8. Granulocytes Neutrophils Band cells Eosinophils Basophils (segmented or not) Mononuclear cells Lymphocytes (many types) Monocytes Dendritic cells Divisions of leukocytes

9. Innate immunity Granulocytes (i.e. neutrophils) Macrophages Dendritic cells Natural killer (NK) cells Adaptive immunity Lymphocyte B cells T cells Cytotoxic T cells (CTLs) Helper T cells (Th) Memory cells Immune system cells

10. Neutrophils • Granulocyte • Phagocytes • Short life span (hours) • Very important at “clearing” bacterial infections • Cytoplasmic granules

11. Eosinophils • A granulocyte • A cell-killing cells • Orange granules contain toxic compounds • Important in parasitic infections

12. Basophils • A granulocyte • A cell-killing cells • Blue granules contain toxic and inflammatory compounds • Important in allergic reactions

13. Lymphocytes • Many types; important in both humoral and cell-mediated immunity • B-cells produce antibodies • T- cells • Cytotoxic T cells • Helper T cells • Memory cells • NK cells

14. Monocytes/Macrophage • Monocyte is a young macrophage • There are tissue-specific macrophages • MØ process antigen, are phagocytes and produce cytokines (esp., IL1 & IL6)

15. Dendritic cells • Found mainly in lymphoid tissue • Function as antigen presenting cells (APC) • Most potent stimulator of T-cell response

16. Low molecular weight, soluble proteins that are produced in response to an antigen and function as chemical messengers for regulating the innate and adaptive immune system Innate immune system Macrophages and Dendritic cells Tumor necrosis factor-alpha (TNF-) Interleukin-1 (IL-1) Interleukin-12 (IL-12) Adaptive immune system T-lymphocytes Interleukin-2 (IL-2) Interleukin-4 (IL-4) Cytokines

17. Innate immunity First line of defense (present in all individuals at all times) Immediate (0 – 4 hours) Non-specific Does not generate lasting protective immunity Adaptive immune response (late: > 96 hours) Is initiated if innate immune response is not adequate (> 4 days) Antigen-specific immunity Generates lasting protective immunity (e.g. Antibodies, memory T-cells) Innate vs. adaptive immunity

18. Innate immunity First line of defense Adaptive (acquired) immunity Takes time to develop Humoral immunity (antibody–mediated specific immunity) Cell-mediated immunity (The aspect of the adaptive immune response where antigen-specific T cell have a main role) Active immunity Passive or maternal immunity Injection of Immunoglobulin Absorption of maternal antibodies Immune system divisions

19. The first line of defense: Penetration of the epithelial surface of the body by microorganism (e.g. bacteria) Engulfment of microorganism by macrophages, neutrophils, and dendritic cells Release of cytokines and chemokines Inflammation (Immunology animation: Janeway) http://www.blink.biz/immunoanimations/# Innate immune system

20. Killing by granulocytes • Macrophages and neutrophils recognize pathogen by means of cell-surface receptors • Example: mannose receptor, CD14 receptor, scavenger receptors, glucan receptor etc. • Binding of MØ/neutrophils with pathogen leads to phagocytosis • Bound pathogen is surrounded by phagocyte membrane • Internalized (phagosome) • Killing of pathogen (Phagolysosome*) • Oxidative burst (synthesis of hydrogen peroxide (H2O2)or free oxygen radicals) • Acidification • Antimicrobial peptides (e.g. defensins) • * Phagolysosome = lysosome +phagosome

21. Lipid mediators Cytokines Phagocytosis Mannose receptor Lysosome Phagosome Scavenger receptor LPS receptor (CD14) Bacteria binding to macrophage receptors initiate the release of cytokines and small lipid mediators of inflammation Phagolysosome The macrophage expresses receptors for many bacterial constituents Macrophages engulf and digest bacteria to which they bind

22. Cell killing – NK cells • NK cells do not require prior immunization or activation • They attach to ‘target’ cells • Cytotoxic granules are released onto surface of cell • Effector proteins penetrate cell membrane and induce programmed cell death

23. Chemokines Cytokines Proteins Fluids Inflammation Inflammatory cells migrate into tissue, releasing inflammatory mediators that cause pain Bacteria trigger macrophages to release cytokines and chemokines Vasodilation and increased vascular premeability cause redness, heat, and swelling

24. Initiated by ingestion of pathogen by an immature dentritic cell Antigen-presenting cell (APC) Dendritic cells, macrophages, and B cells Migrate through lymph to the regional lymph nodes Interact with naive T lymphocytes (present antigen to activate T cells) Proliferation Differentiation (Show annimation: Janeway (2001) IV (The immune response – 8-2: Dentritic-cell migration Adaptive immune system

25. Differentiation of APC B cell Dendritic cell Macrophages Antigen-presenting cells are distributed differentially in the lymph node

26. Antigen receptors with single specificity (T and B cells) Gene re-arrangement T and B cells have 2 distinct recognition systems for detecting pathogens T cells - recognize intracellular pathogens (T cell receptors, TCR) B cells – recognize extracellular pathogens (immunoglobins, BCR) Clonal selection Interaction of antigen and lymphocyte receptor Activation of lymphocyte Differentiation (progeny with identical specificity) Lymphocytes (effector cells of the adaptive immune system)

27. A single progenitor cell gives rise to a large number of lymphocytes, each with a different specificity Foreign antigen Clonal selection Removal of potentially self-reactive immature lymphocytes by clonal deletion Self antigen Self antigen Pool of naïve lymphocytes Proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells Effector cells eliminate antigen

28. Humoral immune response V region; At binding • Cell-surface immunoglobulin receptors (BCR) detect extracellular pathogens • Once activated, secrete immunoglobulins as soluble antibodies • Antibodies • Variable region (2 identical antigen-binding sites) • Constant region (determines how antibody disposes of the pathogen once it is bound) Fc region

29. Pathogen (virus or bacteria) B cell MHC II B cell Production of antibodies Pathogen is internalized and degraded Plasma cells B cell binds pathogen TH1 B cells differentiate into antibody-secreting plasma cells Produce antibodies against pathogen Peptides from the pathogen are presented (MHC II) to the T cell resulting in the activation of the B cell B cell proliferation

30. Antibody classes • IgM (pentimer) • IgG • IgA (Dimer) • IgD • IgE [Ab] Primary Secondary

31. Antibody interactions Antibodies can participate in host defenses in 3 main ways: • Neutralization • Ab bind and neutralize bacterial toxins, bacteria and virus particles – preventing interaction with host cells • Ingestion by macrophages • Opsonization • Allows recognition by phagocytes or NK cells (antibody-dependent cell mediated cytotoxicity, ADCC) • Ingestion or killing • Complement activation • Activation of complement system • Ingestion by phagocytes

32. Antigen recognition by T-cells • T cells detect presence of intracellular pathogens • T cells receptors • Peptide fragments • Major histocompatibility complex (MHC) • MHC I (cytotoxic T cells /CD8) • MHC II (T helper (1 and 2)/ CD4) • Cell death

33. Activates MHC II TH2 B cell Antigen recognition by T-cells TH2 cells recognize antigen presented by MHC II and activates B cells TH1 cells recognize antigen presented by MHC II and activates macrophages Cytotoxic T cells recognize antigen presented by MHC I and kills the cell Kills Activates MHC I MHC II Cytotoxic T cell Virus-infected cell TH1 Macrophage Dead intracellular bacteria Anti-toxin antibodies Apoptotic cell

34. Th1 and Th2 response To Th1 Th2 INF- IL-4 IL-10 IL-5 IL-6 IL-13 IL-2 TNF- NK MØ IL-8 B cell Tc PMN

36. The end