The immune system's T-cells react to foreign protein fragments and therefore are crucial to combating viruses and bacteria. Errant cells that attack the body's own material are in most cases driven to cell death. Some of these autoreactive T-cells, however, undergo a kind of re-education to become "regulatory T-cells" that keep other   more »

Helper T cells are actually quite important and interesting. They are activated by Interleukin-1, produced by macrophages. Once activated, Helper T cells produce Interleukin-2, then interferon, and other chemicals. These chemicals activate B cells so that they produce antibodies. The complexity and level of interaction   more »