Since environmental factors are known to contribute to the pathogenesis of CD in patients [44], as well as DSS-induced colitis in mice [45], this was assessed in SHIP-1−/− mice that were bred in a high-barrier SPF facility before being shipped at weaning to one of two facilities of differing health status: a higher-barrier SPF facility and a lower-barrier SPF facility. This evidence concerns the gene INPP5D and colitis.