8. The immune system: Adaptive immunity

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  1. necessity of adaptive immunity
    • innate immune response is rapid and often effective but is not always sufficient to eliminate infection
    • innate immunity has no memory
    • another arm of the immune system is needed to clear more serious infections and respond to pathogens in a faster, better manner with memory
  2. steps of adaptive immunity
    • initiated when circulating T lymphocytes recognize specific antigens on the surface of dendritic cells or other antigen presenting cells
    • these T cells proliferate and differentiate into antigen specific effector cells
    • T cells usually target intracellular pathogens
    • B cells that recognize antigens differentiate into plasma cells and secrete anitgen-specific antibodies
    • antibodies usually target extracellular microorganisms and their toxins
  3. Humoral immune response
    • immature B cells in bone marrow, B cells mature in lymphoid tissue
    • express IgM and IgD - antigens bind and activate B cells
    • once activated undergo clonal expansion - differentiate into plasma cells that secrete antibodies
    • some responses are T-cell independent
    • usually directed at extracellular microorganisms and toxins
  4. antibody
    a protein (immunoglobulin) produced by plasma cells (B cells) that recognize a target molecule (antigen) to be foreign
  5. IgG
    protect against bacteria, viruses, enhance phagocytosis, neutralize toxins (crosses placental barrier)
  6. IgA
    protects against infection on mucous membranes
  7. IgM
    protects against early phase of infection; comprises anti-A and anti-B antibodies of ABO blood groups, can lyse microbes
  8. IgD
    serves as receptors for activation of B cells
  9. IgE
    invovled in allergic responses, triggers release of histamine
  10. primary response
    • 5-10 days
    • IgM>IgG
    • limited affinity to antigen
  11. secondary response
    • 1-3 days
    • mostly IgG
    • greater affinity for antigen
  12. combinatorial diversification
    • variable regions are inherited as gene segments
    • how an almost unlimited repertoire of antibodies get generated from a limited set of genes
  13. cell mediated immune response
    • T lymphocytes mature in thymus, migrate to lymphoid tissues
    • become activated when encountering antigen presented by antigen presenting cell
    • once activated, multiply and differentiate - cytotoxic T cells and helper T cells
    • once antigen cleared, most cells undergo apoptosis, others become memory cells
    • usually directed at intracellular pathogens
  14. T cell diversity
    • T helper cells (CD4):
    • - Th1 cells = involved in control of intracellular pathogens, produce cytokines and chemokines to attract other T cells and marcrophages
    • -Th2 cells = activates B cells into antibody producing plasma cells
    • cytotoxic T cells (CD8): kill infected cells
    • regulatory T cells: suppress activation of immune response, play a role in tolerating self-antigens
  15. antigen presentation
    antigens are presented on the cellular surface in conjunction with major histocompatibility complex (MHC) molecule
  16. MHC class I
    • present peptide fragments from proteins in the cytosol (intracellular)
    • recognized by CD8 cytotoxic T cells
  17. MHC class II
    • present peptides derived from phagosomes (extracellular)
    • recognized by CD4 T helper cells
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8. The immune system: Adaptive immunity
2011-07-07 10:18:46
PH162A midterm1

public health microbiology lecture 8
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