T cells (also called T lymphocytes) are white blood cells that defend the body from infectious disease, cancer, and foreign substances. T cells also release chemicals (interleukins) that control the entire immune response, that is, how the body recognizes and defends against disease and infection.
Helper and Killer T Cells
Helper T cells circulate in the body hunting for diseased or infected cells. When the helper T cells find these unwanted cells, the helpers send a signal to the killer (cytotoxic) T cells to come and kill the diseased or infected cells. The helper T cells also tell the B cells (another type of white blood cell, also called a plasma cell) to produce antibodies needed to fight off infection.
Killer T cells are important because they are the only T cells that can directly attack and kill other cells. Activated (or "turned on") cytotoxic T cells kill cells that contain foreign particles (antigens) by attaching to them and injecting a toxic chemical.
