Mice lacking functional IL-21/IL-21R signaling (Il21r−/−) showed attenuated C. rodentium–induced colitis, despite significantly greater fecal bacterial loads than their WT counterparts.6 It was hypothesized that attenuated colitis in Il21r−/− mice could be due to their inability to optimally mount a proinflammatory TH1-biased immunity in response to C. rodentium infection in the colon. This evidence concerns the gene IL21R and colitis.