Chap19b Acquired Immune Response

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