XIAP and Crohn ileitis: Together with data from mice with an IEC-specific deletion of an X-linked inhibitor of apoptosis protein (Xiap), which only develops ileitis upon certain bacterial triggers despite the presence of PC alterations (Gopalakrishnan et al., 2019), these results underline the notion of a complex CD pathogenesis involving environmental cues as well as erroneous signals arising from dysfunctional PCs.