IL23A and Klebsiella pneumonia: However, blockade of IL-23p19 may lead to increased susceptibility to enteric microbial infection, and IL-23p19−/− mice exhibited greatly increased susceptibility and mortality after infection with Klebsiella pneumonia [17] and intestinal bacterium Citrobacter rodentium [18], suggesting that IL-23p19 serves an important role in mucosal protective immunity.