Fig. 4: Colonization of Bacteroides vulgatus increases IL-9-secreting CD4⁺ T cells and exacerbates oxazolone-colitis due to an elevation in fecal succinate.

A Schematic of Bacteroides vulgatus colonization and colitis induction. B Fecal succinate measurement using LC–MS in healthy controls, Oxa alone, and Oxa-colonized with Bacteroides vulgatus. C Body weight recovery in healthy controls, Oxa alone, and Oxa-colonized with Bacteroides vulgatus (n = 6). D Formation of colonic lesions in healthy controls, Oxa alone, and Oxa-colonized with Bacteroides vulgatus (n = 6). E Representative images of distal colons stained with H&E and respective statistics for pathology scores. F Representative FACS plot for IL-9 measurement in helper T cells harvested from the mesentery of healthy controls, oxazolone-treated mice, and Oxa-colonized with Bacteroides vulgatus (n = 6). G Representative qPCR data for the expression of IL-9 and related genes Foxo1, PU.1, and IL-9R. H The expression level of SUCNR1, a surrogate indicator for succinate availability, was measured using qPCR in the MLNs of healthy controls, Oxa alone, and Oxa-colonized with Bacteroides vulgatus. I Schematic showing colonization of Bacteroides vulgatus followed by anti-IL-9 and SUCNR1 antagonist (7a) treatment. J Reduction in body weight in healthy controls, Oxa alone, Oxa-colonized with Bacteroides vulgatus, Oxa-colonized with Bacteroides vulgatus plus 7a, and Oxa-colonized with Bacteroides vulgatus plus anti-IL-9 treatment (n = 6). K Formation of colonic lesions in healthy controls, Oxa alone, Oxa-colonized with Bacteroides vulgatus, Oxa-colonized with Bacteroides vulgatus plus 7a, and Oxa-colonized with Bacteroides vulgatus plus anti-IL-9 treatment (n = 6). L Representative images of distal colons stained with H&E and respective statistics for pathology scores of various groups. M Representative qPCR data for the expression of IL-9 and associated genes in healthy controls, Oxa alone, Oxa-colonized with Bacteroides vulgatus, Oxa-colonized with Bacteroides vulgatus plus 7a, and Oxa-colonized with Bacteroides vulgatus plus anti-IL-9 treatment (n = 6). N The expression level of SUCNR1, a surrogate indicator for succinate availability, was measured using qPCR in the MLNs of healthy controls, Oxa alone, Oxa-colonized with Bacteroides vulgatus, Oxa-colonized with Bacteroides vulgatus plus 7a, and Oxa-colonized with Bacteroides vulgatus plus anti-IL-9 treatment (n = 6). *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 (One-way ANOVA or two-way ANOVA).