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T Cells and Immunity

T Cells and Immunity. Antigen Recognition T cells only recognize antigens that are bound to glycoproteins in plasma membranes . T Cells and Immunity. MHC Proteins The membrane glycoproteins that bind to antigens Genetically coded in chromosome 6 The major histocompatibility complex (MHC)

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T Cells and Immunity

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  1. T Cells and Immunity • Antigen Recognition • T cells only recognize antigens that are bound to glycoproteins in plasma membranes

  2. T Cells and Immunity • MHC Proteins • The membrane glycoproteins that bind to antigens • Genetically coded in chromosome 6 • The major histocompatibility complex (MHC) • Differs among individuals

  3. T Cells and Immunity • Two Classes of MHC Proteins • Class I • Found in membranes of all nucleated cells • Class II • Found in membranes of antigen-presenting cells (APCs) • Found in lymphocytes

  4. T Cells and Immunity • Class I MHC Proteins • Pick up small peptides in cell and carry them to the surface • T cells ignore normal peptides • Abnormal peptides or viral proteins activate T cells to destroy cell

  5. T Cells and Immunity • Class II MHC Proteins • Antigenic fragments • From antigenic processing of pathogens • Bind to Class II proteins • Inserted in plasma membrane to stimulate T cells

  6. T Cells and Immunity Figure 20–16 Antigens and MHC Proteins.

  7. T Cells and Immunity Figure 20–16 Antigens and MHC Proteins.

  8. T Cells and Immunity • Antigen-Presenting Cells (APCs) • Responsible for activating T cells against foreign cells and proteins

  9. T Cells and Immunity • Phagocytic APCs • Free and fixed macrophages • In connective tissues • Kupffer cells • Of the liver • Microglia • In the CNS

  10. T Cells and Immunity • Non-phagocytic (pinocytic) APCs • Langerhans cells • In the skin • Dendritic cells • In lymph nodes and spleen

  11. T Cells and Immunity • Antigen Recognition • Inactive T cell receptors • Recognize Class I or Class II MHC proteins • Recognize a specific antigen • Binding occurs when MHC protein matches antigen

  12. T Cells and Immunity • CD Markers • Also called cluster of differentiation markers • In T cell membranes • Molecular mechanism of antigen recognition • More than 70 types: • designated by an identifying number • CD3 Receptor Complex • Found in all T cells

  13. T Cells and Immunity • CD4 Markers • Found on cytotoxic T cells and suppressor T cells • Respond to antigens on Class I MHC proteins • CD8 Markers • Found on helper T cells • Respond to antigens on Class II MHC proteins

  14. T Cells and Immunity • CD8 or CD4 Markers • Bind to CD3 receptor complex • Prepare cell for activation

  15. T Cells and Immunity • Costimulation • For T cell to be activated, it must be costimulated • By binding to stimulating cell at second site • Which confirms the first signal

  16. T Cells and Immunity • Two Classes of CD8 T Cells • Activated by exposure to antigens on MHC proteins • One responds quickly: • producing cytotoxic T cells and memory T cells • The other responds slowly: • producing suppressor T cells

  17. T Cells and Immunity • Cytotoxic T Cells • Also called killer T cells • Seek out and immediately destroy target cells

  18. T Cells and Immunity Actions of Cytotoxic T Cells • Release perforin: • To destroy antigenic plasma membrane • Secrete poisonous lymphotoxin: • To destroy target cell • Activate genes in target cell: • That cause cell to die

  19. T Cells and Immunity Figure 20–17 Antigen Recognition by and Activation of Cytotoxic T Cells.

  20. T Cells and Immunity • Slow Response • Can take up to 2 days from time of first exposure to an antigen for cytotoxic T cells to reach effective levels

  21. T Cells and Immunity • Memory TC Cells • Produced with cytotoxic T cells • Stay in circulation • Immediately form cytotoxic T cells if same antigen appears again

  22. T Cells and Immunity • Suppressor T Cells • Secrete suppression factors • Inhibit responses of T and B cells • Act after initial immune response • Limit immune reaction to single stimulus

  23. T Cells and Immunity • Helper T Cells • Activated CD4 T cells divide into • Active helper T cells (TH cells): • secrete cytokines • Memory TH cells: • remain in reserve

  24. T Cells and Immunity Figure 20–18 Antigen Recognition and Activation of Helper T Cells.

  25. T Cells and Immunity • Four Functions of Cytokines • Stimulate T cell divisions • Produce memory TH cells • Accelerate cytotoxic T cell maturation • Attract and stimulate macrophages • Attract and stimulate NK cells • Promote activation of B cells

  26. T Cells and Immunity Figure 20–19 A Summary of the Pathways of T Cell Activation.

  27. B Cells and Immunity • B Cells • Responsible for antibody-mediated immunity • Attack antigens by producing specific antibodies • Millions of populations, each with different antibody molecules

  28. B Cells and Immunity • B Cell Sensitization • Corresponding antigens in interstitial fluids bind to B cell receptors • B cell prepares for activation • Preparation process is sensitization

  29. B Cells and Immunity • B Cell Sensitization • During sensitization, antigens are • Taken into the B cell • Processed • Reappear on surface, bound to Class II MHC protein

  30. B Cells and Immunity Figure 20–20 The Sensitization and Activation of B Cells.

  31. B Cells and Immunity • Helper T Cells • Sensitized B cell is prepared for activation but needs helper T cell activated by same antigen • B Cell Activation • Helper T cell binds to MHC complex • Secretes cytokines that promote B cell activation and division

  32. B Cells and Immunity • B Cell Division • Activated B cell divides into • Plasma cells • Memory B cells

  33. B Cells and Immunity • Plasma Cells • Synthesize and secrete antibodies into interstitial fluid • Memory B Cells • Like memory T cells, remain in reserve to respond to next infection

  34. B Cells and Immunity • Antibody Structure • Two parallel pairs of polypeptide chains • One pair of heavy chains • One pair of light chains • Each chain contains • Constant segments • Variable segments

  35. B Cells and Immunity • Five Heavy-Chain Constant Segments • Determine five types of antibodies • IgG • IgE • IgD • IgM • IgA

  36. B Cells and Immunity • Variable Segments of Light and Heavy Chains • Determine specificity of antibody molecule

  37. B Cells and Immunity • Binding Sites • Free tips of two variable segments • Form antigen binding sites of antibody molecule • Which bind to antigenic determinant sites of antigen molecule • Antigen-Antibody Complex • An antibody bound to an antigen

  38. B Cells and Immunity

  39. B Cells and Immunity

  40. B Cells and Immunity • A Complete Antigen • Has two antigenic determinant sites • Binds to both antigen-binding sites of variable segments of antibody • B Cell Sensitization • Exposure to a complete antigen leads to • B cell sensitization • Immune response

  41. B Cells and Immunity • Hapten (also called partial antigen) • Must attach to a carrier molecule to act as a complete antigen • Dangers of Haptens • Antibodies produced will attack both hapten and carrier molecule • If carrier is “normal” • Antibody attacks normal cells • For example, penicillin allergy

  42. B Cells and Immunity • Five Classes of Antibodies • Also called immunoglobulins (Igs) • Are found in body fluids • Are determined by constant segments • Have no effect on antibody specificity

  43. B Cells and Immunity Figure 20–21a–b Antibody Structure and Function.

  44. B Cells and Immunity Figure 20–21c–d Antibody Structure and Function.

  45. B Cells and Immunity • Seven Functions of Antigen-Antibody Complexes • Neutralization of antigen-binding sites • Precipitation and agglutination: formation of immune complex • Activation of complement • Attraction of phagocytes • Opsonization: increasing phagocyte efficiency • Stimulation of inflammation • Prevention of bacterial and viral adhesion Figure 22–22

  46. B Cells and Immunity • Primary and Secondary Responses to Antigen Exposure • Occur in both cell-mediated and antibody-mediated immunity Figure 22–22

  47. B Cells and Immunity • Primary and Secondary Responses to Antigen Exposure • First exposure • Produces initial primary response • Next exposure • Triggers secondary response • More extensive and prolonged • Memory cells already primed

  48. B Cells and Immunity • The Primary Response • Takes time to develop • Antigens activate B cells • Plasma cells differentiate • Antibody titer (level) slowly rises

  49. B Cells and Immunity • The Primary Response • Peak response • Can take 2 weeks to develop • Declines rapidly • IgM • Is produced faster than IgG • Is less effective

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