Perforin-2 Permeabilizes the Envelope of Phagocytosed Bacteria

Perforin-2, the product of the MPEG1 gene, limits the spread and dissemination of bacterial pathogens in vivo. It is highly expressed in murine and human phagocytes, and macrophages lacking Perforin-2 are compromised in their ability to kill phagocytosed bacteria. In this study we used Salmonella typhimurium as a model intracellular pathogen to elucidate the mechanism of Perforin-29s bactericidal activity. In vitro Perforin-2 was found to facilitate the degradation of antigens contained within the envelope of phagocytosed bacteria. In contrast, degradation of a representative surface antigen was found to be independent of Perforin-2. Consistent with our in vitro results a protease sensitive, periplasmic superoxide disumutase (SodCII) contributed to the virulence of S. typhimurium in Perforin-2 knockout but not wild-type mice. In aggregate our studies indicate that Perforin-2 breaches the envelope of phagocytosed bacteria facilitating the delivery of proteases and other antimicrobial effectors to sites within the bacterial envelope.