T-Lymphocyte, T-Cell, T-Cell Activation, T-Cell Surface Receptor, T-Helper Cell, Helper T-Cell, CD4+ Cell, T-Cytotoxic Cell, Cytotoxic T-Cell, CD8+ Cell

  • Definitions
  1. T-Lymphocytes (T-Cells)
    1. T-Cells are responsible Cell-Mediated Immunity
    2. T-Cells target Intracellular Pathogens (e.g. viruses and Intracellular Bacteria) and cancer cells
  • Physiology
  1. T-Cells
    1. Derived in Bone Marrow
    2. Migrate to Thymus
      1. Maturation and Differentiation into two cell lines with different T-Cell Receptors (CD4 and CD8)
    3. Release into peripheral circulation
  2. T-Cell Surface Receptors and Accessory Molecules
    1. T-Cell Receptors (TCR)
      1. Bind the Antigen on the Antigen Presenting Cell (APC)
      2. Similar structure to Antibody
        1. Each chain (a, b, g or d) has a constant region (C) and a variable region (V)
        2. Variable region (V) on each chain forms Antigen binding site
      3. TCR Types (based on polypeptides ab or gd)
        1. TCR-alpha-beta (TCRab+)
        2. TCR gamma-delta (TCRgd+)
      4. Plasticity
        1. T-Cell Receptors (TCR) have variable regions whose genes may be rearranged
        2. Rearranging variable region genes allows for a reflex change in TCR binding target
          1. Similar mechanism to B-Cell Immunoglobulin Gene modification
    2. T-Cell Signal Transduction related Costimulatory Receptors (Allows for T-Cell Activation)
      1. CD3 and Zeta (Z) are part of T-Cell Receptor Complex (along with TCR)
        1. CD3 and Zeta (Z) are involved with signal transduction from T-Cell surface to inside of T-Cell
        2. T-Cell Receptors together with CD3 and Zeta (Z) are known as T-Cell Receptor Complex
        3. T-Cell Receptor Complex binds Peptide-MHC Complex as first signal in T-Cell Activation
      2. CD28
        1. Binds Ligand B7 (receptor found on APCs) as part of second signal in T-Cell Activation
    3. T-Cell Co-Receptors
      1. CD4 binds peptide/Antigen-MHC Class 2 complex on surface of Antigen Presenting Cells (APC)
      2. CD8 binds peptide/Antigen-MHC Class 1 complex on surface of Antigen Presenting Cells (APC)
    4. Adhesion Molecules (T Cell Surface Receptor proteins that bind Ligands on Antigen Presenting Cell)
      1. Lymphocyte Function Associated Antigen-1 or LFA-1
        1. Binds Ligands intracellular Adhesion Molecule 1-3 (ICAM 1-3)
      2. Cluster of Differentiation 2 (CD2)
        1. Binds Ligand LFA-3
      3. Cluster of Differentiation 44 (CD44)
        1. Binds Ligand Hyaluronate
  3. Naive T-Cell Activation
    1. TCellActivation.jpg
    2. T-Cell Receptor (TCR) binds to MHC-Antigen complex on Antigen Presenting Cells (APC)
    3. T-Cell Surface CD28 binds to B7 Ligand on Antigen Presenting Cell
    4. T-Cell Surface LFA-1 (Lymphocyte Function Associated Antigen) binds ICAM1 on Antigen Presenting Cells
    5. Interleukin-2 (IL2) produced by naive T Cells
      1. Stimulate T Cell proliferation
  • Types
  • T-Cells
  1. Effector Cells
    1. T-Helper Cells (CD4+ Cells)
      1. Releases Interferon
        1. Stimulates Phagocytosis by Macrophages
        2. Activates Natural Killer Cells
        3. Suppresses viral replication
      2. Releases interleuken 2
        1. Promotes T-Cell proliferation (esp. memory cells)
        2. Promotes B-Cell proliferation (memory cells and plasma cells)
    2. T-Cytotoxic Cells (CD8+ Cells)
      1. Target and destroy tumor cells and virus-infected cells
  2. Other Cells
    1. Memory Cells
    2. Apoptosis of some cells not otherwise differentiated
  • References
  1. Guyton and Hall (2006) Medical Physiology, p. 419-50
  2. Mahmoudi (2014) Immunology Made Ridiculously Simple, MedMaster, Miami, FL