Final answer:
The Fas ligand activates fas molecules on the surface of target cells, leading to apoptosis. It is expressed on cytotoxic T cells and NK cells, playing an integral part in eliminating infected or cancerous cells from the body.
Step-by-step explanation:
The Fas ligand is a transmembrane protein on the surface of a killer lymphocyte that activates fas molecules on the surface of a target cell. The Fas ligand is crucial in the immune system, expressed on both cytotoxic T cells and NK cells (Natural Killer cells).
When the Fas ligand binds to the fas molecule on the target cell, it sends a signal that induces apoptosis, effectively causing the death of the target cell. This process is vital for eliminating cells that are infected with pathogens or are cancerous, therefore playing a significant role in the body's defense mechanism against these harmful cells.