Alternations in fecal microbiota composition
Next, we assessed alterations in fecal microbiota composition in type 1 AIP following PSL treatment. Analysis at the order level revealed that induction of remission by PSL treatment was accompanied by the disappearance of Enterobacteriales and Fusobacterialesfrom the gut of two and one of the three AIP patients, respectively (Fig. 2, 3).
Relative abundance of each bacteria at the genus level is shown in Fig. 4A. Although the composition of fecal microbiota did not differ significantly between active and remitted diseases at the genus level, the following trends were seen in several bacterial species. Colonization by Klebsiella spp. was detected in two of the three patients before treatment with PSL. Surprisingly, clinical remission induced by PSL was accompanied by complete disappearance ofKlebsiella spp. in two of the three patients (Cases 1 and 2, Fig. 4B). These data were consistent with complete disappearance ofEnterobacteriales at the order level in two of three paints after PSL treatment. In contrast, the relative abundance of Ruminococcus spp. was higher in the feces of all patients after treatment (Fig. 4A, B). A marked reduction in colonization of Fusobacterium spp.after PSL treatment was seen in one patient (Case 3) who did not harborKlebsiella spp. before PSL treatment. AlthoughBifidobacterium spp. were highly abundant in the feces of mice exhibiting AIP in our previous study [20], the relative abundance ofBifidobacterium spp. was comparable before and after the treatment in this study. Thus, induction of remission by PSL was accompanied by complete disappearance of Klebsiella spp. from the feces of two type 1 AIP patients and by a marked reduction inFusobacterium spp. from those of one patient who did not harbor the former bacterium. These fecal microbiota data suggest that colonization by Klebsiella spp. might be involved in the development of type 1 AIP in patients who harbor this bacterium.