Final answer:
The Fas-FDD complex binds with the Fas ligand to induce apoptosis in target cells, playing a critical role in immune system regulation and cellular homeostasis.
Step-by-step explanation:
The Fas-FDD complex binds with the Fas ligand, which is a molecule expressed on cytotoxic T cells and natural killer (NK) cells. When the Fas ligand binds to the Fas receptor on a target cell, it triggers a cascade of events leading to apoptosis, which is a process of programmed cell death. This mechanism is vital for maintaining homeostasis in the body by eliminating cells that are infected, damaged, or otherwise marked for destruction.