Exposure to inhaled diesel exhaust particles increases mucin 2 (MUC2) expression in the small intestine of C57Bl/6 male mice, regardless of probiotic treatment. Representative images of MUC2 expression in the three regions of the small intestine of C57Bl/6 male mice on a high-fat diet exposed to saline (CON; A–C), diesel exhaust particles (DEP-35 µg PM; D–F), saline and probiotics (CON + PRO, 0.3 g/d of Ecologic® Barrier probiotics; G–I), or diesel exhaust particles and probiotics (DEP + PRO, 0.3 g/d of Ecologic® Barrier probiotics; J–L) twice a week for 4 w. Panels show merged images within the duodenum (A,D,G,J), jejunum (B,E,H,K), and ileum (C,F,I,L). Green fluorescence indicates MUC2 expression and blue fluorescence indicates nuclear staining (Hoechst). Graph (M) shows the histological analysis of MUC2 by region, (N) shows the global (cumulative expression of three portions) analysis of MUC2 expression in the small intestine, and (O) shows the global mean normalized gene expression of MUC2 mRNA transcript expression in the small intestine, as determined by RT-qPCR. 40× magnification, scale bar = 100 µm. Data are depicted as ± SEM with * p < 0.05 compared to CON, † p < 0.05 compared to DEP, and ‡ p < 0.05 compared to CON + PRO.