The function of T cells is to perform a variety of immune responses in the body, according to National Multiple Sclerosis Society. T cells are one of two types of white blood cells that help immune function.
T cells are so called because they are formed in an organ called the thymus gland. Helper T cells, regulatory T cells and cytotoxic T cells are three broad categories of T cells listed by the National Multiple Sclerosis Society. Functions of T cells include direct attacks on bacteria, viruses and foreign tissues and producing substances called cytokines that direct responses and activities in other immune cells.