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T – Lymphocyte

  1. Cellular immunity     
    1. T-lymphocytes: 60-70% of peripheral blood lymphocytes
    2. Present in paracortical areas of LN & periarteriolar sheaths of spleen.
    3. T cells have; Ag specific TCR9570 - a & 13 polypeptide chains - bind antigen
    4. Others: γ /δ- Mostly on epithelial/mucosal interface
      1. Demonstration of TCR gene rearrangement by southern Blot is a molecular marker of T cell lineage
      2. CD3 <-- Non variable (involved in signal transduction)
      3. CD4 (cluster of differentiation 4) is a glycoprotein expressed on the surface of T helper cells, regulatory T cells, monocytes, macrophages, and dendritic cells.
  2. Other CD markers:
    CD4: 60% of T cells - Co-operative in T cell
    CD8: 30% of T cells - Activation
    CD4: CD8 = 2:1 (normal) Q
    CD4 binds to non-polymorphic portion of Class II MHC molecules
    CD8 to Class I MHC molecules Q


Fig : The T-cell receptor (TCR) complex.

  1. Activation of T cells: Two signals Q
    1. TCR binding to MHC bound Ag, CD4/CD8 co-receptors enhance this signal
    2. Interaction of CD-28 with co-stimulatory molecules B7-1 & B7-2 (CD 80 and CD 86)
      (In absence of signal 2; T cell => Apoptosis)
      CD4 + T cell: Master regulator
  1. Two types of CD4+ helper cells:

1. TH1 subset + secretes IL-2, IFN-Y and act on macrophages

                     → Involved in

  1. Delayed HS,     
  2. Macrophage activation  
  3. Synthesis of IgG Ab

2. TH2 subset → produces IL-4, IL-5 and act on eosinophils

                        → Aids in synthesis of IgE

     CD8 + T cells: can secrete CKs of THI type
  1. Primarily cytotoxic cells.          
    T cell Ass. Markers: CD 1. CD2. C63, CD4:. CD5, CD7, CD8, CD28 :

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