A Newly Identified Role for IL-22 in Bladder Immunity

Bacterial and parasitic urinary tract infections(UTI) affect many, but our understanding of associated immunity remains poor. Prior work indicates interleukin-22(IL-22) is a key cytokine during infection of other epithelia. We hypothesized IL-22 is crucial during UTI. IL-22-null(KO) and wild-type(wt) mice underwent bladder wall injection with S. haematobium eggs or transurethral infection with uropathogenic E. coli UTI89. IL-22 and its soluble binding protein, IL-22BP, were increased in the bladder after S. haematobium egg injection. Genes typically induced by IL-22(CXCL2, REG3G[antimicrobial defense protein]], S100A8, S100A9, and Areg) were expressed at higher levels following S. haematobium egg injection. IL-22 stimulation of bladder tissue induced REG3B expression. IL-22 receptor alpha-1 expression was detectable in the urothelium by immunofluorescence and qPCR. Injection of S. haematobium eggs into IL-22-KO vs wt mice triggered differential expression of genes related to transferase activity(transferring alkyl or aryl groups) and epithelial cell development. Numerous uroplakin genes were downregulated in egg-injected, IL-22-KO mice versus their wt counterparts. These decreases in uroplakin expression suggest that, as in the gut, IL-22 is important for replenishing the epithelium during infection-related injury. Following transurethral infection with UTI89, IL-22-KO mice had lower bacterial counts in their urine, bladder, and kidneys. Giving stabilized IL-22 cytokine (IL-22-Fc) to UTI89-infected mice led to higher kidney bacterial counts and increased morbidity. Our data suggest that IL-22 is indeed important in urinary tract immunity, and may interfere with clearance of bacteria from the urinary tract, potentially through its role in maintenance of mature urothelium.