In the absence of curdlan and relative to GF ileum, Il23a and Grp78 gene expression significantly increased in mice colonized with L.m. but not P.g. or ASF (Figure 3, B and C), suggesting a basal ER stress response in the presence of L.m. Consistent with the role of IL-23p19 in ileitis (Figure 1B and Figure 2A) and of the relationship of IL-23p19 to ER stress (9, 13–15), curdlan administration increased Il23a and sXbp1 expression in mice colonized with L.m. and P.g., but not ASF (Figure 3, B and C). Here, HSPA5 is linked to Crohn ileitis.