Joseph A. Trapani, Preethi Eldi, Dion Kaiserman, Antony Yaron Matthews, Iona S. Schuster, Geeta Chaudhri, Phillip I. Bird, Peter Fleming, Jérôme D. Coudert, Gunasegaran Karupiah, Christopher E. Andoniou, Mariapia A. Degli-Esposti, Kevin Y. T. Thia, Vivien R. Sutton, Matthew E. Wikstrom, Andoniou, Christopher E, Sutton, Vivien R, Wikstrom, Matthew E, Fleming, Peter, Thia, Kevin YT, Matthews, Antony Y, Kaiserman, Dion, Schuster, Iona S, Coudert, Jerome D, Eldi, Preethi, Chaudhri, Geeta, Karupiah, Gunasegaran, Bird, Phillip I, Trapani, Joseph A, and Degli-Esposti, Mariapia A
Many immune response genes are highly polymorphic, consistent with the selective pressure imposed by pathogens over evolutionary time, and the need to balance infection control with the risk of auto-immunity. Epidemiological and genomic studies have identified many genetic variants that confer susceptibility or resistance to pathogenic micro-organisms. While extensive polymorphism has been reported for the granzyme B (GzmB) gene, its relevance to pathogen immunity is unexplored. Here, we describe the biochemical and cytotoxic functions of a common allele of GzmB (GzmBW) common in wild mouse. While retaining ‘Asp-ase’ activity, GzmBW has substrate preferences that differ considerably from GzmBP, which is common to all inbred strains. In vitro, GzmBW preferentially cleaves recombinant Bid, whereas GzmBP activates pro-caspases directly. Recombinant GzmBW and GzmBP induced equivalent apoptosis of uninfected targets cells when delivered with perforin in vitro. Nonetheless, mice homozygous for GzmBW were unable to control murine cytomegalovirus (MCMV) infection, and succumbed as a result of excessive liver damage. Although similar numbers of anti-viral CD8 T cells were generated in both mouse strains, GzmBW-expressing CD8 T cells isolated from infected mice were unable to kill MCMV-infected targets in vitro. Our results suggest that known virally-encoded inhibitors of the intrinsic (mitochondrial) apoptotic pathway account for the increased susceptibility of GzmBW mice to MCMV. We conclude that different natural variants of GzmB have a profound impact on the immune response to a common and authentic viral pathogen., Author Summary Granzymes (Gzm) are serine proteases expressed by cytotoxic T cells and natural killer cells, and are important for the destruction of virally infected cells. To date, the function of these molecules has been assessed exclusively in common laboratory mouse strains that express identical granzyme proteins. In wild mouse populations, variants of granzyme B have been identified, but how these function, especially in the context of infections, is unknown. We have generated a novel mouse strain expressing a granzyme B variant found in wild mice (GzmBW), and exposed these mice to viral infections. The substrates cleaved by GzmBW were found to differ significantly from those cleaved by the GzmBP protein, which is normally expressed by laboratory mice. Alterations in substrate specificity resulted in GzmBW mice being significantly more susceptible to infection with murine cytomegalovirus, a common mouse pathogen. Our findings demonstrate that polymorphisms in granzyme B can profoundly affect the outcome of infections with some viral pathogens.