Final answer:
Cytotoxic T cells are the key component of the cell-mediated immune system and attack and destroy infected cells. Helper T cells orchestrate immune responses and enhance the functions of other immune cells. Regulatory T cells prevent damaging immune responses and cytotoxic T cells destroy cells infected by intracellular pathogens.
Step-by-step explanation:
Cytotoxic T cells (TC) are the key component of the cell-mediated part of the adaptive immune system and attack and destroy infected cells. Tc cells are particularly important in protecting against viral infections; this is because viruses replicate within cells where they are shielded from extracellular contact with circulating antibodies. Once activated, the Tc creates a large clone of cells with one specific set of cell-surface receptors, as in the case with proliferation of activated B cells. As with B cells, the clone includes active Tc cells and inactive memory Tc cells. The resulting active Tc cells then identify infected host cells.
Helper T cells serve as the central orchestrators that help activate and direct functions of humoral and cellular immunity. In addition, helper T cells enhance the pathogen-killing functions of macrophages and NK cells of innate immunity. Regulatory T cells prevent undesirable and potentially damaging immune responses, protecting against autoimmune disorders. Cytotoxic T cells are the primary effector cells for cellular immunity and destroy cells infected by intracellular pathogens.