A T-cell is a type of blood cell. T-cells belong to a group of white blood cells (WBCs) called lymphocytes. WBCs protect the body from infection.
The main job of T-cells is to fight infection. There are a number of different types of T-cells that act in many ways to identify, directly attack and destroy infectious agents. Along with other WBCs, they play a major role in the immune system, which guards the body against infection.
After they are produced in the bone marrow, these cells spend some time maturing and developing in an organ in the chest called the thymus (why they are named T-cells). After maturation, T-cells are present in the blood and in lymph nodes.
T-cells may be affected in diseases of the immune system, like AIDS, and in cancers, like lymphoma.