Final answer:
In T cells, helper T cells mediate effector functions through the secretion of cytokines, cytotoxic T cells directly target infected cells, and regulatory T cells regulate the immune response.
Step-by-step explanation:
The part in T cells that handles the mediating effector functions can vary depending on the type of T cell in question. Helper T cells (Th), which bear the CD4 molecule, function by secreting cytokines that enhance the immune response. These helper T cells can differentiate into TH1, TH2, and TH17 cells, each with distinct functions related to stimulating adaptive and innate immune defenses, or into memory T cells which are long-lived and respond quickly to secondary exposures. In contrast, cytotoxic T cells (Tc) directly target and destroy infected cells. Regulating the immune response and preventing overactivation that may lead to autoimmune disorders is the main function of regulatory T cells.