A T cell is a type of white blood cell present in the human body. The term T cell is short for Thymus cell, the organ in which this type of white blood cell matures. T cells are important in maintaining the body's immune system, and are critical in the fight against harmful invading substances.

When a virus or other invader enters your system, your body undergoes an immunological response. Certain cells have receptors that can identify an attacking substance, and can activate different cells in your body to find and destroy harmful invaders. People with a strong immune system typically have a high amount of white blood cells and T cells. Patients with autoimmune diseases or who are suffering from cancer are frequently subject to blood cell counts that can tell doctors how well their T cells and other helpful cells are surviving and fighting their illness.

There are several different types of T cells in the body, each with a specific function. Helper T cells are able to quickly divide and assist in the whole body's immunity response to attack by creating a helpful protein called cytokine. Another type of T cell, often called a memory cell, helps the body remember to fight off repeat infections, preventing you from catching the same illness more than once.

One of the most useful types of T cells also carries a huge drawback. Cytotoxic cells work to destroy tumors or mutated cells, much like soldiers repelling an invader. Unfortunately, in transplants, this type of cell can misidentify a transplanted organ as a threat, and attack it. Cytotoxic cells are considered one of the main factors in transplant rejection.

T cells are considered extremely important in the fight against autoimmune diseases, especially in the cases of Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS.) Many of the treatments currently in use for these viruses involve stimulating T cell production and response in order to fight the detrimental effects of these conditions. Our naturally occurring “killer” T cells are not able to effectively fight HIV, so scientists have developed a variety of techniques to improve the cells and make the cell receptors more sensitive to this deadly virus.

Because the study of cellular function is still relatively new, there is still much science does not understand about T cells and how they work. As they continue to study these helpful cells, it is believed they will be able to reduce cell-caused transplant rejection and improve treatments for autoimmune diseases. In the meantime, you may wish to thank your T cells once in a while, for performing a vital service that keeps you healthy and alive.