Final answer:
The CD antigen that mediates apoptosis is CD95, which triggers programmed cell death when binding to Fas ligand on a target cell.
Step-by-step explanation:
The CD antigen responsible for mediating apoptosis is CD95. This antigen, also known as Fas, interacts with the Fas ligand molecule expressed on cytotoxic T cells and natural killer (NK) cells. When CD95 binds to the Fas ligand on a target cell,
it signals the target cell to undergo programmed cell death, which is a crucial mechanism for maintaining homeostasis in the body and immune system regulation. CD4 and CD8 molecules are expressed on different subsets of T cells with diverse functions in the immune response.
In particular, CD4+ T cells do not induce apoptosis in other cells; instead, they help activate B cells and CD8+ T cells. The latter, when become cytotoxic T cells, can kill infected cells by releasing perforin and granzyme molecules that induce apoptosis. However, CD95 specifically plays a direct role in the mechanism triggering apoptosis.