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Chap19b Acquired Immune Response


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Chap19b Acquired Immune Response

  1. 1. Resistance and the Immune System: Acquired Immunity Chapter 19
  2. 2. <ul><li>Acquired Immunity responds to, distinguishes between and remembers specific pathogen it has encountered. </li></ul><ul><li>Four Important Attributes: </li></ul><ul><ul><li>Specificity </li></ul></ul><ul><ul><ul><li>Antigens are microbes or microbe parts that provoke an immune response </li></ul></ul></ul><ul><ul><ul><li>Immune system recognizes small parts of the antigen called antigenic determinants or epitopes </li></ul></ul></ul><ul><ul><ul><li>Immune deficiency is the loss of the body’s ability to respond to antigens and epitopes </li></ul></ul></ul>Overview
  3. 3. <ul><li>Tolerance of Self </li></ul><ul><ul><li>Regulatory T cells prevent other T cells from attacking “self” cells </li></ul></ul><ul><ul><ul><li>Autoimmune diseases occur when self-tolerance breaks down </li></ul></ul></ul><ul><ul><li>If nonimmunogenic molecules (haptens) are linked to proteins, they may not be recognized as “self” </li></ul></ul><ul><ul><ul><li>Thus they might provoke an immune response (allergies) </li></ul></ul></ul><ul><li>Minimal “Self” Damage </li></ul><ul><ul><li>An immune response must be strong enough to eliminate the pathogen, yet controlled so as not to cause extensive damage </li></ul></ul><ul><li>Immunological Memory </li></ul><ul><ul><li>Immunological memory is the ability to “remember” past pathogen exposures </li></ul></ul><ul><ul><ul><li>The body fights off any subsequent infections </li></ul></ul></ul>Overview
  4. 4. <ul><li>The cornerstone of acquired immunity are the lymphocytes </li></ul><ul><ul><li>B lymphocytes (B cells) are involved in producing antibodies against epitopes </li></ul></ul><ul><ul><li>T lymphocytes (T cells) provide resistance through lysis of infected or abnormal cells </li></ul></ul><ul><ul><ul><li>Subsets: T helper cells, T suppressor cells, T cytotoxic cells and T delayed type hypersensitivity </li></ul></ul></ul>Two Complementary Responses
  5. 5. <ul><li>Humoral Immune Response </li></ul><ul><ul><li>The humoral immune response involves: </li></ul></ul><ul><ul><ul><li>activation of B cells </li></ul></ul></ul><ul><ul><ul><li>production of antibodies against the identified antigen </li></ul></ul></ul><ul><ul><ul><li>Highly specific, body can generate antibodies against any antigen or epitope </li></ul></ul></ul><ul><li>Cell Mediated Immune Response </li></ul><ul><ul><li>If the microbes enter cells, antibodies are useless </li></ul></ul><ul><ul><ul><li>Then the cell mediated immune response is activated to eliminate “nonself” cells </li></ul></ul></ul><ul><ul><ul><li>T cells have receptor proteins; the highly specific receptor proteins on the lymphocyte surface implies that even before an antigen enters the body, immunocompetent B and T cells are already waiting. </li></ul></ul></ul>Two Complementary Responses
  6. 6. <ul><li>In the fetus, lymphocytes arise from hematopoietic stem cells in the yolk sac and bone marrow </li></ul><ul><ul><li>They develop into: </li></ul></ul><ul><ul><ul><li>Myeloid progenitors, which become: </li></ul></ul></ul><ul><ul><ul><ul><li>red blood cells </li></ul></ul></ul></ul><ul><ul><ul><ul><li>most white blood cells </li></ul></ul></ul></ul><ul><ul><ul><li>Lymphoid progenitors, which become lymphocytes </li></ul></ul></ul><ul><li>T lymphocytes are formed in the thymus </li></ul><ul><li>B cells are formed in the bone marrow </li></ul>Stem Cells
  7. 7. Ontogeny
  8. 8. <ul><li>Maturation of both T and B cells insertion of surface receptor proteins. </li></ul><ul><li>B cells can recognize antigenic determinants on an antigen; T cells depends on surface receptor proteins + MHC proteins </li></ul><ul><li>MHC: embedded in the membranes of all cell bodies </li></ul><ul><ul><li>2 classes (“self”): Class I MHC proteins (nucleated cells) and Class II MHC (B lymphocytes, macrophages) </li></ul></ul><ul><li>Entry of antigen --- phagocytosis (macrophage) --- MHC-peptide complexes --- ANTIGEN PRESENTING CELLS (dendritic cells) </li></ul><ul><li>Unprocessed antigens stimulate the immune response poorly. </li></ul>T and B Cells Have Receptors to Recognize Antigens Recognition Commitment
  9. 9. <ul><li>Responds to cells infected with pathogens </li></ul><ul><li>Cellular Immunity Relies on T-Lymphocyte Receptors and Recognition </li></ul><ul><ul><li>Cytotoxic T cells have T-cell receptors (TCRs) and CD8 coreceptor proteins </li></ul></ul><ul><ul><li>Naïve T cells have TCRs and CD4 coreceptor proteins </li></ul></ul><ul><ul><ul><li>Naïve T cells can help with both humoral and cell mediated immunity </li></ul></ul></ul><ul><ul><ul><li>HIV attaches to the CD4 receptor and infects the cell </li></ul></ul></ul><ul><li>TCRs and coreceptors allow T cells to recognize and bind to the major histocompatibility complex (MHC) </li></ul>Cell Mediated Immune Response
  10. 10. <ul><li>Naïve T Cells Mature into Effector T Cells </li></ul>
  11. 11. <ul><li>Host cells infected by viruses can: </li></ul><ul><ul><li>degrade viral antigens </li></ul></ul><ul><ul><li>present peptide fragments with MHC-1 proteins on the cell surface </li></ul></ul><ul><li>Activated cytotoxic T cells recognize and bind to the MHC-1/peptide complex on infected cells </li></ul><ul><li>They release toxic substances such as perforin and granzymes to: </li></ul><ul><ul><li>cause cell death </li></ul></ul><ul><ul><li>expose pathogens to antibodies </li></ul></ul><ul><li>T cells can also recognize and kill tumor cells </li></ul><ul><li>Memory T lymphocytes – provide long term immunity </li></ul>T cells
  12. 12. <ul><li>Antigen exposure activates only T and B cells with receptors that recognize specific epitopes on that antigen </li></ul><ul><li>B and T cell clones contain lymphocytes that develop into effector cells that which target pathogens </li></ul><ul><li>B cells – activation begins when antigen enter a lymphoid organ and bring antigenic determinants close to the appropriate B cells that can respond </li></ul>Clonal Selection
  13. 13. <ul><li>TH 2 Cells Initiate the Cellular Response to Humoral Immunity </li></ul><ul><li>The Process of Antibody-Mediated Immunity </li></ul><ul><li>T-dependent antigens </li></ul><ul><li>T independent antigens </li></ul><ul><li>Superantigens </li></ul><ul><li>Plasma Cells </li></ul>
  14. 14. <ul><li>Antibodies are of a class of proteins called immunoglobulins </li></ul><ul><li>Epitope recognition requires antibodies to have a special structure of: </li></ul><ul><ul><li>2 identical heavy (H) chains </li></ul></ul><ul><ul><li>2 identical light (L) chains </li></ul></ul><ul><li>Each light and heavy chain has: </li></ul><ul><ul><li>A constant region, which determines the location and functional class of the antibody </li></ul></ul><ul><ul><li>A variable region, which contains different amino acids for the many antibodies produced </li></ul></ul>Antibodies Recognize Specific Epitopes
  15. 15. <ul><li>The variability allows formation of the specific antigen binding site </li></ul><ul><li>The Fab fragment of an antibody combines with the Epitope </li></ul><ul><li>The Fc fragment performs functions in: </li></ul><ul><ul><li>opsonization </li></ul></ul><ul><ul><li>activation of the complement system </li></ul></ul><ul><ul><li>allergic reactions </li></ul></ul>Antibodies Recognize Specific Epitopes
  16. 16. <ul><li>IgM is the first (but short-lived) Ig to appear in circulation after B cell stimulation </li></ul><ul><ul><li>presence indicates a very recent infection; fetal infections </li></ul></ul><ul><li>IgG (gamma globulin) is the major circulating antibody </li></ul><ul><ul><li>It provides immunity to the fetus and newborn (maternal antibody) </li></ul></ul><ul><ul><li>Appears 24-48 h after antigenic stimulation (booster shots) </li></ul></ul><ul><li>IgA provides resistance in the respiratory and gastrointestinal tracts </li></ul><ul><ul><li>It is found in colostrum; also located in tears, saliva </li></ul></ul><ul><li>IgE plays a role in allergic reactions by sensitizing cells </li></ul><ul><li>IgD is a cell surface receptor on B cells; also called membrane antibody and is important in the activation of B cells </li></ul>Five Immunoglobulin Classes
  17. 17. <ul><li>A primary antibody response occurs the first time the body encounters a pathogen </li></ul><ul><li>A secondary antibody response is more powerful and sustained </li></ul><ul><ul><li>It occurs with a subsequent infection by the same pathogen </li></ul></ul>Two Types of Antibody Responses
  18. 18. <ul><li>Antibody Interactions Mediate the Disposal of Antigens (Pathogens) </li></ul><ul><ul><li>Formation of antigen-antibody complexes result in the antigen: </li></ul></ul><ul><ul><ul><li>death </li></ul></ul></ul><ul><ul><ul><li>inactivation </li></ul></ul></ul><ul><ul><ul><li>increased susceptibility </li></ul></ul></ul>
  19. 19. <ul><li>The membrane attack complex causes cell lysis </li></ul>
  20. 20. Summary of the Immune Response