Final answer:
Interleukin-2 (IL-2) is the cytokine responsible for promoting the proliferation of activated cytotoxic T cells (Tc), which are essential for the immune system's response to infections, particularly viral infections.
Step-by-step explanation:
Interleukin-2 (IL-2) is the cytokine that stimulates proliferation (clonal expansion) of the activated Tc cell (cytotoxic T lymphocyte). Cytokines play a critical role in the immune system as soluble, short-range cell-to-cell communication molecules that govern the maturation, growth, and responsiveness of particular cell populations, including lymphocytes. Notably, within the adaptive immune response, activated helper T lymphocyte (Th) cells, particularly the Th1 subtype, produce IL-2 to promote the clonal expansion of both cytotoxic T cells (Tc) and themselves.
Cytotoxic T cells are essential in the body's defense against infections, especially viral ones, by inducing apoptosis in target cells. They are activated by antigen-presenting cells (APCs) presenting an antigen with MHC I molecules and the interaction of CD8 with the receptor complex. Following activation, the production of cytokines, including IL-2, by Th1 cells further stimulates the activated cytotoxic T cells, leading to their clonal expansion and differentiation into effector cytotoxic T cells or memory cells ready for subsequent exposures to the same antigens.