T-cell lymphocytes
The type of white BLOOD cell (LEUKOCYTE) responsible for CELL-MEDIATED IMMUNITY. T-cell lymphocytes come to maturity in the THYMUS during childhood, which is why they are called T-cells. During the maturation process, T-cell lymphocytes “learn” how to recognize self and nonself antigens so they can distinguish between cells that belong to the body and cells that are foreign. Such a safeguard is necessary to keep T-cell lymphocytes from attacking the body’s own cells. The thymus destroys lymphocytes that do not learn this distinction. After the thymus releases mature T-cell lymphocytes into the blood circulation, they differentiate into several subtypes. These include
- cytotoxic T-cell lymphocytes, also called killer T-cells or CD8 cells, which respond to nonself antigens to kill the cells that bear them
- helper T-cells, also called CD4 cells, which release CYTOKINES that stimulate B-CELL LYMPHOCYTE and cytotoxic T-cell lymphocyte activity
- memory T-cells, which carry specific antibodies and circulate in the blood for rapid activation should the same ANTIGEN reappear
- suppressor T-cells, which call off the IMMUNE RESPONSE when the threat to the body ends
The SPLEEN, the lymph nodes, and the MUCOSAASSOCIATED LYMPHATIC TISSUE (MALT) throughout the body contain millions of T-cell lymphocytes. T-cell lymphocytes also circulate in the blood and the LYMPH. T-cell lymphocytes may also be the source of disease, such as in HIV/AIDS (the VIRUS attaches to CD4 helper T-cells) and cutaneous T-cell lymphoma (CTCL), a form of cancer.
For further discussion of T-cell lymphocytes within the context of the structures and functions of the immune system, please see the overview section “The Immune System and Allergies.”
See also ANTIBODY; ANTIBODY-MEDIATED IMMUNITY; CLUSTERS OF DIFFERENTIATION; LYMPH NODE; MAJOR HISTOCOMPATIBILITY COMPLEX (MHC); NATURAL KILLER (NK) CELL.
