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Immune System

Immune System. Biology for Majors. Components of the Immune System. Pathogens. Pathogens cause diseases in their hosts Pathogens include bacteria, viruses, protists, fungi and other infectious organisms. Physical and Chemical Barriers.

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Immune System

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  1. Immune System Biology for Majors

  2. Components of the Immune System

  3. Pathogens • Pathogens cause diseases in their hosts • Pathogens include bacteria, viruses, protists, fungi and other infectious organisms

  4. Physical and Chemical Barriers • Pathogens are killed or inactivated on the skin by desiccation (drying out) and by the skin’s acidity. In addition, beneficial microorganisms that coexist on the skin compete with invading pathogens, preventing infection • Eyes use tears to rinse away pathogens • Mucus membranes have mucus secretions that trap and rinse away pathogens • Cilia in the nasal passages and respiratory tract push the mucus with the pathogens out of the body • The low pH of the stomach inhibits the growth of pathogens • Blood proteins that bind and disrupt bacterial cell membranes • Urination flushes pathogens from the urinary tract

  5. Mast Cells Dilate blood vessels and induce inflammation through release of histamines and heparin. Recruit macrophages and neutrophils. Involved in wound healing and defense against pathogens, but can also be responsible for allergic reactions Located in connective tissues, mucous membranes

  6. Macrophages • Phagocytic cells that consume foreign pathogens and cancer cells. Stimulate response of other immune cells. • Migrate from blood vessels into tissues

  7. Natural Killer Cells • Kill tumor cells and virus-infected cells • Circulate in blood and migrate into tissues

  8. Dendritic cells • Present antigens on their surface, thereby triggering adaptive immunity • Present in tissues in epithelial tissue, including skin, lung and tissues of the digestive tract. Migrate to lymph nodes upon activation

  9. Monocytes • Differentiate into macrophages and dendritic cells in response to inflammation • Stored in the spleen, move through blood vessels to infected tissues

  10. Neutrophils • First responders at the site of infection or trauma, these abundant phagocytic cells represent 50–60% of all leukocytes. Release toxins that kill or inhibit bacteria and fungi and recruit other immune cells to the site of infection • Migrate from blood vessels into tissues

  11. Basophils • Responsible for defense against parasites. Release histamines that cause inflammation and may be responsible for allergic reactions • Circulate in blood and migrate to tissues

  12. Eosinophils • Release toxins that kill bacteria and parasites but also cause tissue damage • Circulate in blood and migrate to tissues

  13. Interferons Interferons are cytokines that are released by a cell infected with a virus. Response of neighboring cells to interferon helps stem the infection

  14. Phagocytosis and Inflammation In response to a cut, mast cells secrete histamines that cause nearby capillaries to dilate. Neutrophils and monocytes leave the capillaries. Monocytes mature into macrophages. Neutrophils, dendritic cells and macrophages release chemicals to stimulate the inflammatory response. Neutrophils and macrophages also consume invading bacteria by phagocytosis

  15. The Classic Pathway for the Complement Cascade

  16. Adaptive Immunity • Adaptive immunity occurs after exposure to an antigen either from a pathogen or a vaccination • activated when the innate immune response is insufficient to control an infection • In fact, without information from the innate immune system, the adaptive response could not be mobilized • There are two types: • the cell-mediated immune response is carried out by T cells • the humoral immune response is controlled by activated B cells and antibodies

  17. Antigen-Presenting Cells

  18. Antigen An antigen is a macromolecule that reacts with components of the immune system. A given antigen may contain several motifs that are recognized by immune cells. Each motif is an epitope. In this figure, the entire structure is an antigen, and the orange, salmon and green components projecting from it represent potential epitopes

  19. T cells

  20. T Cell Receptor A T cell receptor spans the membrane and projects variable binding regions into the extracellular space to bind processed antigens via MHC molecules on APCs

  21. B Cell Receptors B cell receptors are embedded in the membranes of B cells and bind a variety of antigens through their variable regions. The signal transduction region transfers the signal into the cell.

  22. Natural Killer (NK) Cells Recognize Healthy Cells

  23. Mucosa-associated Lymphoid Tissue

  24. Memory B Cells

  25. Primary and Secondary Immune Response In the primary response to infection, antibodies are secreted first from plasma cells. Upon re-exposure to the same pathogen, memory cells differentiate into antibody-secreting plasma cells that output a greater amount of antibody for a longer period of time

  26. Lymph (a) Lymphatic vessels carry a clear fluid called lymph throughout the body. The liquid enters (b) lymph nodes through afferent vessels. Lymph nodes are filled with lymphocytes that purge infecting cells. The lymph then exits through efferent vessels

  27. Spleen The spleen filters blood. Blood enters the spleen through arteries and exits through veins. The spleen contains two types of tissue: red pulp and white pulp. Red pulp consists of cavities that store blood. Within the red pulp, damaged red blood cells are removed and replaced by new ones. White pulp is rich in lymphocytes that remove antigen-coated bacteria from the blood

  28. Antibody Structure

  29. IgA Found in mucous, saliva, tears, and breast milk. Protects against pathogens

  30. IgD Part of the B cell receptor. Activates basophils and mast cells

  31. IgE Protects against parasitic worms. Responsible for allergic reactions

  32. IgG Secreted by plasma cells in the blood. Able to cross the placenta into the fetus

  33. IgM May be attached to the surface of a B cell or secreted into the blood. Responsible for early stages of immunity

  34. Antibody Function

  35. Affinity, Avidity, and Cross-reactivity

  36. Immunodeficiency Immunodeficiency is the failure, insufficiency, or delay in the response of the immune system, which may be acquired or inherited

  37. Hypersensitivity Allergy is an immune reaction that results from immediate hypersensitivities in which an antibody-mediated immune response occurs within minutes of exposure to a harmless antigen

  38. Autoimmunity Autoimmunity is a type of hypersensitivity to self antigens such as Lupus, right

  39. Practice Question What is the connection between molecular mimicry and autoimmune diseases? Why do pathogens use molecular mimicry?

  40. Quick Review • What are immediate and induced innate immune responses? • What is adaptive immunity? • What are the structure and function of antibodies? • What are immunodeficiency and hypersensitivity?

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