Cathepsin W

Cathepsin W (CTSW), historically named lymphopain, is a papain-family cysteine protease whose expression is largely confined to cells of the cytotoxic lymphocyte lineage, most prominently natural killer cells and CD8-positive cytotoxic T cells. Transcripts are weak or absent from most other tissues, making CTSW one of the most lineage-restricted cathepsin genes. The enzyme is predicted to follow the standard preproenzyme maturation pathway, yet its physiological substrates and activation partners remain undefined, and mouse knockout studies have not revealed striking phenotypes. Proposed functions center on cytotoxic lymphocyte biology, and CTSW expression has served as a marker of NK cell activity in immunological analyses.