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

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II. Definitions

  1. T-Lymphocytes (T-Cells)
    1. T-Cells are responsible Cell-Mediated Immunity
    2. T-Cells are named for where they mature and differentiate (Thymus)
    3. T-Cells target Intracellular Pathogens (e.g. viruses and Intracellular Bacteria) and cancer cells
      1. Humoral Immunity (antibodies) are in contrast unable to affect Intracellular Pathogens

III. 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

IV. Types: T-Cells

  1. Effector Cells
    1. T-Helper Cells (CD4+ Cells)
      1. T-Helper Cell Proliferation and Activation is stimulated by Antigen Presenting Cells (see above)
        1. Binding to T-Cell Surface Receptors and Accessory Molecules AND
        2. Interleukin 1 or IL-1 (released from Antigen Presenting Cells)
          1. T-Helper Cells then develop Interleukin 2 (IL-2) receptors once activated
      2. Releases Interferon
        1. Stimulates Phagocytosis by Macrophages
        2. Activates Natural Killer Cells
        3. Suppresses viral replication
      3. Releases interleuken 2
        1. Promotes T-Cell proliferation (including Cytotoxic T Cells, and subsequently memory cells)
        2. Promotes B-Cell proliferation (memory cells and plasma cells) to generate antibodies
      4. Additional functions
        1. Aid Macrophages in destroying phagocytized Bacteria
        2. Contribute to Graft Rejection, responding to the graft's foreign MHC, activating T-Cytotoxic Cells
    2. T-Cytotoxic Cells (CD8+ Cells)
      1. Responds to cell surface MHC I combined with degraded peptide Antigens (foreign material marker)
        1. Specific cytotoxic T cells form for each Antigen (e.g. virus)
        2. Cytotoxic T-Cell Specificity is similar to Antibody and T-Helper Cell Specificity
      2. Cytotoxic T Cells Target and destroy cells marked as foreign
        1. Tumor cells
        2. Virus-infected cells
        3. Transplanted or grafted cells (Transplant Rejection)
    3. Memory Cells
      1. Cytotoxic T Cells proliferate and form Memory Cells, promoted by Helper T Cells
  2. Suppressor Cells
    1. T Suppressor Cells (Regulatory T Cells)
      1. Suppress immune cell activation
      2. Prevents autoimmune reactions by promoting self tolerance
  3. Other Cells
    1. Apoptosis of some cells not otherwise differentiated

V. References

  1. Guyton and Hall (2006) Medical Physiology, p. 419-50
  2. Mahmoudi (2014) Immunology Made Ridiculously Simple, MedMaster, Miami, FL

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Related Studies

Ontology: T-Lymphocyte (C0039194)

Definition (NCI_NCI-GLOSS) A type of immune cell that can attack foreign cells, cancer cells, and cells infected with a virus. T lymphocytes can also help control immune responses. A T lymphocyte is a type of white blood cell.
Definition (NCI) A thymocyte-derived lymphocyte of immunological importance that is long-lived (months to years) and is responsible for cell-mediated immunity. T lymphocyte cells form rosettes with sheep erythrocytes and, in the presence of transforming agents (mitogens), differentiate and divide. These cells have the characteristic T3 surface marker and may be further divided into subsets according to function, such as helper, cytotoxic, etc.
Definition (CSP) lymphocytes responsible for cell-mediated immunity, formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes; when exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen.
Definition (MSH) Lymphocytes responsible for cell-mediated immunity. Two types have been identified - cytotoxic (T-LYMPHOCYTES, CYTOTOXIC) and helper T-lymphocytes (T-LYMPHOCYTES, HELPER-INDUCER). They are formed when lymphocytes circulate through the THYMUS GLAND and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen.
Concepts Cell (T025)
MSH D013601
SnomedCT 57184004
CPT 1011953
LNC LP14634-7, LA4470-6
English Lymphocyte, Thymus-Dependent, Lymphocytes, Thymus-Dependent, T Lymphocytes, T-Cells, T-Lymphocytes, Thymus Dependent Lymphocytes, Thymus-Dependent Lymphocyte, Thymus-Dependent Lymphocytes, LYMPHOCYTES J, lymphocytes T cells, thymus-dependent lymphocyte, lymphocytes T cells (lab test), T cells, T-lymphocyte, thymus derived lymphocyte, t-cells, t cell, t lymphocyte, t cells, t lymphocytes, t-lymphocytes, t-lymphocyte, t-cell, T Cell Lymphocyte, T lymphocyte, T cell, T-cell, T lymphocyte (cell), T Cells, T-Cell, T Cell, T-Lymphocyte
Russian ТИМУС-ЗАВИСИМЫЕ ЛИМФОЦИТЫ, LIMFOTSITY VILOCHKOVOI ZHELEZY, T-LIMFOTSITY, TIMUSZAVISIMYE LIMFOTSITY, T-KLETKI, TIMUS-ZAVISIMYE LIMFOTSITY, T-КЛЕТКИ, T-ЛИМФОЦИТЫ, ЛИМФОЦИТЫ ВИЛОЧКОВОЙ ЖЕЛЕЗЫ, ТИМУСЗАВИСИМЫЕ ЛИМФОЦИТЫ
French Ly T, Lymphocytes T, Lymphocytes thymodépendants, Lymphocytes thymo-dépendants, Cellules T, Lymphocyte T
Swedish T-lymfocyter
Czech T-buňky, T-lymfocyty, T-buňka
Finnish T-imusolut
Italian Cellule T, Linfociti timo-dipendenti, Linfociti T
Japanese 胸腺依存リンパ球, 胸腺リンパ球, リンパ球-胸腺, リンパ球-T, T細胞, Tリンパ球
German LYMPHOZYTEN J, T-Lymphozyten, T-Zellen, Thymusabhängige Lymphozyten
Croatian T-LIMFOCITI, LIMFOCITI T
Polish Limfocyty T
Norwegian T-celler, Thymusavhengige lymfocytter, T-lymfocytter
Spanish célula T, linfocito T (célula), linfocito T, Linfocitos Timo-Dependientes, Linfocitos T, Células T
Dutch Lymfocyt, T-, T-cel, T-lymfocyt, T-lymfocyten, Thymusafhankelijke lymfocyt
Portuguese Células T, Linfócitos Timo-Dependentes, Linfócitos T
Derived from the NIH UMLS (Unified Medical Language System)

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