T-Lymphocyte

Aka: 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

1. See Also
   1. White Blood Cell (Leukocyte)
   2. Lymphocyte
   3. Immune System
   4. B-Lymphocyte (B Cell)
   5. Natural Killer Cell (NK cell)
2. 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
3. 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. 
      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
4. 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
5. References
   1. Guyton and Hall (2006) Medical Physiology, p. 419-50
   2. Mahmoudi (2014) Immunology Made Ridiculously Simple, MedMaster, Miami, FL