T-cells

T-cells are major players in the cell mediated response in adaptive immunity. T-cells recognize processed antigen in contrast to B cells which recognize native, non-processed antigen.

Types of T cells:

There are 2 main subpopulations of T cells; T helper (T_H) cells and T cytotoxic (T_C) cells. T cells which display a CD4 glycoprotein generally function as T_H and are class II restricted whereas T_C cells generally display a CD8 glycoprotein and are class I restricted. The ratio of T_H to T_C cells is generally 2:1.

There are also a subpopulation of T cells called regulatory T cells. Several subsets of regulatory T (Tr) cells with distinct phenotypes and distinct mechanisms of action have been identified. These include type 1 Tr cells (Tr1) cells which secrete high levels of IL-10 and low to moderate levels of transforming growth factor (TGF-B, type 3 T (Th3) cells, which primarily secrete TGF-beta, and CD4+CD25+ T cells, which inhibit immune responses through cell-cell contact.

In addition to the various CD4+ Tr populations, recent studies have identified CD8+ Tr cells, which secrete either IL-10 or TGF-beta.

T cells are also classified as naive, effector and memory T cells.

The T Cell Receptor (TCR):

T Cell Maturation: