T cells (also known as Thymocytes cells) or
T lymphocytes are a type of
lymphocyte (in turn, a type of
white blood cell) that play a central role in
cell-mediated immunity. They can be distinguished from other lymphocytes, such as
B cells and
natural killer cells (NK cells), by the presence of a
T-cell receptor (TCR) on the cell surface. They are called T cells because they mature in the
thymus (although some also mature in the
tonsils). The several subsets of T cells each have a distinct function. The majority of human T cells
rearrange their alpha/beta T cell receptors and are termed alpha beta T cells and are part of
adaptive immune system. Specialized
gamma delta T cells, which comprise a minority of T cells in the human body (more frequent in ruminants), have invariant TCR (with limited diversity), can effectively present
antigens to other T cells and are considered to be part of the
innate immune system.