Cathepsin C limits acute viral infection independently of NK cell and CD8+ T-cell cytolytic function

Destruction of target cells by cytotoxic T lymphocytes (CTLs) or natural killer (NK) cells requires the coordinated action of the pore forming protein perforin (Pfp) and the granzyme (Gzm) family of serine proteases. The activation of a number of serine proteases, including GzmA and B, is predominately mediated by cathepsin C (CatC). Deficiencies in CatC-null mice were therefore expected to replicate the defects observed in GzmAB-deficient mice. We have previously determined that GzmAB-deficient mice exhibit increased susceptibility to murine cytomegalovirus (MCMV) infection. Here, we have compared the ability of CatC(-/-) mice to control MCMV infection with that of GzmAB-deficient animals. We found that CatC(-/-) mice have organ-specific defects in the ability to control MCMV replication, a phenotype that is distinct to that observed in GzmAB(-/-) mice. Significantly, the cytolytic function of CatC-deficient NK cells and CTLs elicited during infection was indistinguishable from that of wild-type cells. Hence, CatC is involved in limiting MCMV replication; however, this effect is independent of its role in promoting effector cytolytic activity. These data provide evidence for a novel and unexpected role of CatC during viral infection. Immunology and Cell Biology (2011) 89, 540-548; doi:10.1038/icb.2010.115; published online 26 October 2010