A novel molecule purified from Staphylococcus aureus mutant produces γδ T cell-mediated IL-17A in mice peritoneum and protects MRSA-derived skin abscess expansion

Abstract

Abstract Staphylococcus aureus, a commensal bacterium in human, causes a wide range of human diseases from soft tissue infections to lethal systemic infections. But, immune-competent people are highly resistant to these diseases, indicating that unknown host defense response(s) can protect host. An effective immune response to S. aureus requires a rapid activation of innate immunity in the shape of γδ-T cells mediated IL-17 production for bacterial clearance. We hypothesized that an unidentified staphylococcal-cell wall derived molecule(s) that can activate host innate γδ-T cells is generated after S. aureus infection in healthy people. To purify this molecule(s) in mice, we generated 11 different S. aureus mutant strains, in which genes involved in staphylococcal cell wall components bio-syntheses were mutated. The mutant cells were acetone-treated to inactivate and extract toxic molecules, and then injected intra-peritoneal cavity of mice. When peritoneal lavage fluid collected 5 hr after injection was examined which mutant bacteria can produce IL-17A, three mutants produced IL-17A. To purify active fractions capable of γδ T cell-mediated IL-17A production, acetone-treated mutant bacterium was solubilized with two different peptidoglycan hydrolyzing enzymes. Then, active molecules were purified to homogeneity on ion-exchange columns. By pre-injection of purified molecule or acetone-treated mutant bacteria, the expansion of USA 300 MRSA-mediated skin abscess was inhibited, leading to a lower bacterial numbers and decrease of abscess lesion size at the site of infection. These results suggest that a novel molecule producing γδ T cell-derived IL-17A in peritoneum protected MRSA-derived skin abscess expansion in mice.