In vitro, KLK5 (Kallikrein 5) catalyzes the slow cleavage of a four-residue aminoterminal propeptide from proKLK8 (pro-Kallekrein 8), to generate active KLK8. The abundance of KLK8 in the stratum corneum and its serine endopeptidase activity are consistent with a role for KLK8 in formation of the stratum corneum, desquamation, or both. Physiological substrates for KLK8 remains to be identified, however, as do possible additional activators of it (Eissa et al. 2011). A possible pathogenic role for KLK8 is suggested by the recent demonstration that it can mediate the extracellular cleavage of the L1 capsid protein of human papilloma viruses, facilitating their infection of human host cells (Cerqueira et al. 2015).