perforin

This term is a specialized biochemical designation used almost exclusively within immunology and cell biology. It describes a specific mechanism of cellular warfare where the protein acts as a physical drill, puncturing the lipid bilayer of a target cell to facilitate the entry of granzymes.

Because it refers to a specific molecular species, it is treated as an uncountable mass noun in scientific literature. Researchers refer to the "expression of perforin" or "perforin levels" rather than counting individual protein molecules.