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B-Lymphocyte

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B-Lymphocyte, B Cell, B-Cell Activation, B-Lymphocyte Surface Receptor, B-Cell Surface Receptor

  • See Also
  1. Humoral Immunity (includes Immunoglobulin)
  2. White Blood Cell (Leukocyte)
  3. Lymphocyte
  4. Immune System
  5. Natural Killer Cell (NK cell)
  6. T-Lymphocyte (T-Cell)
  • Definitions
  1. B-Lymphocyte (B Cell)
    1. B-Cells are responsible for Humoral Immunity
    2. B-Cells are named for where they were first found (Bursa of Fabricus in birds)
    3. Responsible for Antigen-specific Antibody (plasma cells) and secondary future responses (memory cells)
  • Physiology
  • General
  1. Derivation
    1. Fetal Liver
    2. Bone Marrow Pluripotent Stem Cells
  2. Peripheral Migration to Secondary Lymphoid Tissue
    1. Spleen
    2. Lymph Nodes
    3. Peyer's Patches (Small Bowel)
  • Physiology
  • B-Cell Activation
  1. Images
    1. BCellActivation.jpg
  2. Recognition
    1. Antigen binds B-Lymphocyte Surface Receptor (BCR)
    2. BCR binding activates B-Lymphocyte
      1. T-Cell Independent Antigen (e.g. inert Antigens) alone activate B-Cells
        1. Signal 1
          1. B-Cell Surface Receptor (BCR) binding to Antigenic Epitopes (repeat Amino Acid sequences)
          2. Signal transduced from cell surface to into cell via Ig alpha and beta
        2. Signal 2
          1. B-Cell co-receptor complex associated CR2 binds Antigen-bound Complement C3d
      2. T-Cell Dependent Antigen (e.g. Microbes) require added stmulus (i.e. T Helper Cells)
        1. B-Cell Surface Receptor (BCR) binds Antigen AND
        2. B-Cells processes and presents Antigen to CD4+ T-Cells (T helper cells)
        3. CD4+ T-Cells (T helper cells) are activated by B-Cell surface Antigens and their co-stimulators
          1. Signal 1 for T-Cell Activation
            1. MHC Class 2 - Antigen Complex bind T-Cell Receptor (TCR)
          2. Signal 2 for T-Cell Activation
            1. Co-stimulators B7-1 and B7-2 bind the T-CellSurface CD28
        4. B Cell proliferation and differentiation is stimulated by T Helper Cell binding
          1. B-Cell CD40 surface Protein is bound by the Cytokine T Helper Cell CD40 Ligand
          2. Cytokines (IL2, IL4, IL5) are released by activated T-Helper Cells
  3. B-Cell Proliferation
    1. Activated Lymphocytes proliferate
  4. B-Cell Differentiation
    1. Plasma Cells (Antibody producing cells)
      1. Survive for days to weeks producing antibodies, and without replicating
      2. Primarily found in Lymph Nodes and Spleen
    2. Memory Cells
      1. Remain in B-Lymphocyte pool ready to respond to the same Antigen in future
      2. Future Antigen response is known as secondary immune response
  • Physiology
  • Plasticity
  1. Isotype Switching
    1. Antibody isotope type (e.g. IgE, IgG, IgM) are defined by the Antibody constant regions (C-Regions)
    2. The C-Regions may be abruptly modified to switch to production of a different Antibody isotope
      1. Example: A B-Cell may switch to IgE production in the case of Parasitic Infection
  2. Immunoglobulin Gene modifications in response to Antigen detection
    1. Antibodies contain hypervariable regions within the variable section (Fab Component)
    2. Hypervariable regions (complementarity-determining region or CDR)
      1. Three heavy chain hypervariable regions
      2. Three light chain hypervariable regions
    3. In response to infection, hypervariable region genes may be rearranged to respond specifically to the organisms
      1. Variations in variable and hypervariable genes result in increased production of organism specific Antibody
  • References
  1. Guyton and Hall (2006) Medical Physiology, p. 419-50
  2. Mahmoudi (2014) Immunology Made Ridiculously Simple, MedMaster, Miami, FL