A streptococcal protease that degrades CXC chemokines and impairs bacterial clearance from infected tissues

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Abstract
Group A Streptococcus (GAS) causes the life‐threatening infection in humans known as necrotizing fasciitis (NF). Infected subcutaneous tissues from an NF patient and mice challenged with the same GAS strain possessed high bacterial loads but a striking paucity of infiltrating polymorphonuclear leukocytes (PMNs). Impaired PMN recruitment was attributed to degradation of the chemokine IL‐8 by a GAS serine peptidase. Here, we use bioinformatics approach coupled with target mutagenesis to identify this peptidase as ScpC. We show that SilCR pheromone downregulates scpC transcription via the two‐component system—SilA/B. In addition, we demonstrate that in vitro , ScpC degrades the CXC chemokines: IL‐8 (human), KC, and MIP‐2 (both murine). Furthermore, using a murine model of human NF, we demonstrate that ScpC, but not the C5a peptidase ScpA, is an essential virulence factor. An ScpC‐deficient mutant is innocuous for untreated mice but lethal for PMN‐depleted mice. ScpC degrades KC and MIP‐2 locally in the infected skin tissues, inhibiting PMN recruitment. In conclusion, ScpC represents a novel GAS virulence factor functioning to directly inactivate a key element of the host innate immune response.