Veterinary Immunology and Serology

T - LYMPHOCYTES

• Progenated T lymphocytes originate from bone marrow stem cells and attracted to thymus.
• They enter thymus at any time of embryonic or post- embryonic period.
• The microenvironment in thymus is essential for the maturation of T cells.
• T cells mature in thymus and hence the name (thymus derived).
• The immature T cells are initially found in the cortex, migrate to medulla and differentiate to mature T cells.
• The mature T cells express its characteristic cell membrane glycoproteins.
• T cells have subpopulations and they express T cell receptors but can be differentiated by the presence or absence of two-membrane molecule i.e.CD4 and CD8.
• Helper T cells have CD4 and T cytotoxic / suppressor cells have CD8 molecules.
• The developing T cells within thymus are called thymocytes.
• They initially populate, proliferate and undergo rearrangements of TCR (T cell receptor) genes. There is surface expression of CD3, TCR, CD4 and CD 8 molecules in the cortex. After maturation they migrate to medulla.

Some of the surface molecules

• T cell receptors (α/β and γ/δ) along with CD3 complex.
• CD 2: Receptor of CD 58
• CD 4: Molecule on the surface of T helper cells
• CD 8: Molecule on the surface of T cytotoxic cells
• CD 71: Receptor for transferring (transport receptor).
• CD 35: complement receptor
• CD 25: Interleukin –2 receptor for T cell growth
• Adherence molecules (integrin family, selectin family etc.).