CTSV (Cathepsin V, Cathepsin L2, CTSL2) is a lysosomal cysteine proteinase that is involved in corneal physiology and in the maintenance of hair follicles and the epidermis. In the brain, it is involved in neuropeptide production (encephalin and NPY) and is found throughout, with particularly high expression in myelinated axons in white matter (corpus callosum, cingulum bundle), the globus pallidus, the emboliform nucleus, the reticular formation, and in neurons of the mesencephalon and myelencephalon. CTSV is a positive marker in colorectal and breast cancer and it is upregulated in the progressive eye disease keratoconus, where it is implicated in oxidative stress. In immunohistochemistry, CTSV has granular cytoplasmic positivity in most tissues, with higher expression in the thymus and testis and moderate positivity in the corneal and conjunctival epithelium and skin. References: Invest. Ophthal. Vis. Sci. 46 (3): 823–832, PMID: 15728537; Cancer Res. 1998 Apr 15;58(8):1624-30, PMID: 9563472; Eur J Cell Biol. 2004 Dec;83(11-12):775-80, PMID: 15679121; Invest Ophthalmol Vis Sci. 2005 Mar;46(3):823-32, PMID: 15728537; Heliyon. 2018 Jul; 4(7): e00673, PMID: 29998195