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The Immune system

The Immune system. Role: protect body against pathogens Pathogens; bacteria, bacterial toxin, viruses, parasites, and fungi. Outline. Anatomy of the Immune system Organization of the body’s defenses Humoral immunity Cell-mediated immunity Immune responses in Health and diseases. Outline.

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The Immune system

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  1. The Immune system • Role: protect body against pathogens • Pathogens; bacteria, bacterial toxin, viruses, parasites, and fungi.

  2. Outline • Anatomy of the Immune system • Organization of the body’s defenses • Humoral immunity • Cell-mediated immunity • Immune responses in Health and diseases

  3. Outline • Anatomy of the Immune system • Organization of the body’s defenses • Humoral immunity • Cell-mediated immunity • Immune responses in Health and diseases

  4. Leukocytes - Phagocytes (phagocytosis): neutrophils, eosinophils, monocytes, macrophages, dendritic cells (skin) - Lymphocytes: Bs and Ts, natural killer cells - Mast cells Lymphoid tissues - primary lymphoid tissues (bone marrow and thymus) - secondary lymphoid tissues Anatomy

  5. Outline • Anatomy of the Immune system • Organization of the body’s defenses • Humoral immunity • Cell-mediated immunity • Immune responses in Health and diseases

  6. Non-specific defenses: no need to decipher pathogen’s identiy. Always present in the body. - Physical barriers - Inflammation - Interferons - Natural cell killers (NK cells) - Complement system Specific defenses:Based onn recognition of the pathogen’s identity Humoral immunity Cell-mediated immunity Organization of the body’s defenses

  7. Physical barriers - skin - mucus - stream of tears or urine - Inflammation Chemical barriers pH (stomach, vagina) enzymes (stomach, tears) Interferons Complement system Non-specific defenses

  8. Inflammation Symptoms of inflammation: • Redness • heat • Swelling • - pain

  9. Macrophage and phagocytosis

  10. Interferon • Protein secreted by a cell currently infected by a virus • Interferon warns the neighboring cells of the impending viral infection • The neighboring cells synthesize proteins that will block the virus from hijacking the cell DNA replication machinery Animation: http://people.eku.edu/ritchisong/interferon2.gif

  11. About 30 blood proteins They become activated either by direct contact with a pathogen or by contact with a bound antibody. In an activated state, they form a complex which opens a hole in a pathogen’s cell membrane  bacterial lysis Complement system also promotes inflammation Complement system

  12. Cytotoxic T cells, lacking markers Able to recognize a wide range of pathogens without prior exposure When recognition and binding occur, the NK cells destroy the pathogen through cell lysis Natural Killer cells = NK cells

  13. Specificity: based on shape recognition of cell surface antigens Diversity: Any shape can be recognized by a B or T-lymphocytes and trigger an immune reaction Memory: once a pathogen has activated the immune system, memory cells remain and will protect against a secondary infection Self-tolerance: the immune system does not attack itself Specific immunity

  14. Macrophages (antigen presenting cell = APC): phagocytize pathogens and present antigens to helper-T lymphocytes Helper-T lymphocytes: secrete lymphokines and activate B and killer T lymphocytes B-lymphocytes: multiply and specialize into plasma cells  secrete antibodies Killer-T lymphocytes: kill (through lysis) infected or cancerous cells Specific immunity = the players

  15. Outline • Anatomy of the Immune system • Organization of the body’s defenses • Humoral immunity • Cell-mediated immunity • Immune responses in Health and diseases

  16. 1- Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell 2- At the same time, some pathogens contact B-cells matching the pathogen’s antigens The helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cells The plasma cells secretes antibodies Antibody-mediated (humoral) immunity = AMI

  17. Figure 23.7

  18. Structures formed by 4 proteins Two main regions: the upper region is highly variable and bind to a specific shape (the antigen) The base region is constant for all antibodies  this region, when the antibody is bound to its antigen, activates the complement system What are antibodies?

  19. Role of the antibodies

  20. Types of antibodies • Antibody = immunoglobulin = Ig • IgG Most abundant. mostly in blood, lymph. able to cross the placenta • IgA  Found in tears, milk, blood, lymph • IgM  First antibody to be secreted. found in blood, lymph. unable to cross placenta • IgD  Found in blood, lymph, on B cells • IgE Found on mast cells, basophils. involved in allergic reaction.

  21. First and second exposures to a pathogen

  22. Once a T, B or killer lymphocytes have made contact with their specific antigen, they are triggered into action but they also divide and form a large amount of identical cells, called a clone. Clonal selection

  23. How can the DNA in the nucleus codes for each type of antibody? Since over a millions of different types are needed, how can the DNA in the nucleus code for each of them? There is clearly not enough DNA to accomplish that. During embryogenesis, several genes coding for the variable portion of the antibody (and each responsible for part of a shape) reshuffle so each combination of genes codes for a specific antibody (and shape). So a stem cell receives the capability to form one single type of antibody. Once formed, they circulate in the body. If they meet and bind to a shape (formed by a protein) present in the body, they are destroyed or deleted, so that only the stem cells responsible for antibodies aimed at foreign pathogens are left. A stem cell able to react with our own proteins and not deleted during fetal life might later trigger an autoimmune disease. Clonal deletion

  24. Outline • Anatomy of the Immune system • Organization of the body’s defenses • Humoral immunity • Cell-mediated immunity • Immune responses in Health and diseases

  25. Cell-mediated immunity • Similar reaction to AMI • The pathogen triggering the reaction is a virus infected cell or a cancerous cell. • Killer T lymphocytes are sensitized by contact and activated by lymphokines secreted by activated helper T lymphocytes

  26. CMI Figure 23.11 (1 of 2)

  27. Clinical applications • Immunization - Active and natural - Active and artificial - Passive and natural - Passive and artificial • Why are we vaccinating against some disease but not other? • Why not Ebola?

  28. Immediate allergic reaction: due to IgE Tissue transplant and tissue rejection: due to cytotoxic T cells Clinical applications Delayed allergic reaction: due to cytotoxic T cells

  29. Beginning of transplant rejection

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