The cytokine IL-22 promotes pathogen colonization by suppressing related commensal bacteria.

Interleukin-22 (IL-22) is highly induced in response to infections with a variety of pathogens, and its main functions are considered to be tissue repair and host defense at mucosal surfaces. Here we showed that IL-22 has a unique role during infection in that its expression suppressed the intestinal microbiota and enhanced the colonization of a pathogen. IL-22 induced the expression of antimicrobial proteins, including lipocalin-2 and calprotectin, which sequester essential metal ions from microbes. Because Salmonella enterica ser. Typhimurium can overcome metal ion starvation mediated by lipocalin-2 and calprotectin via alternative pathways, IL-22 boosted its colonization of the inflamed intestine by suppressing commensal Enterobacteriaceae, which are susceptible to the antimicrobial proteins. Thus, IL-22 tipped the balance between pathogenic and commensal bacteria in favor of a pathogen. Taken together, IL-22 induction can be exploited by pathogens to suppress the growth of their closest competitors, thereby enhancing pathogen colonization of mucosal surfaces.