Pediatric Crohn disease is characterized by Th1 in the terminal ileum and Th1/Th17 immune response in the colon.

Unlabelled: The aim of this study was to assess the expression of inflammatory mediators in the affected terminal ileum and colon in pediatric Crohn disease (CD) patients with different stages of disease. Additionally, we assessed the role of efflux transporters in disease pathogenesis and their correlation with immune response. The study included 26 CD patients (10 newly diagnosed (CD-new), 8 CD-treated, and 8 CD-remission) and 15 control subjects. The terminal ileum IFN-γ, IL-6, and IL-1β were elevated in CD-new, while in the colon, the IFN-γ, IL-17A, and IL-6 were elevated in both CD-new and CD-treated subgroups. SOCS3 expression was elevated in both subgroups with active inflammation at both ileum and colon, while SOCS1 was elevated only in CD-new ileum and CD-treated colon. MDR1 expression in ileum was reduced in both subgroups with active inflammation, while BCRP was reduced only in CD-new subgroup.

Conclusion: New onset pediatric CD is characterized by Th1 response in ileum and mixed Th1/Th17 response in the colon, with elevated expressions of innate IL-6 and IL-1β. SOCS1/SOCS3 expressions seem to be insufficient for the regulation of the immune response. The reduction in MDR1 expression points to its role in the disease pathogenesis. What is Known: • CD is characterized by an aberrant immune response What is New: • The immune response in new onset pediatric CD differs between terminal ileum and colon • MDR1 expression is downregulated at both terminal ileum and colon irrespective of the disease activity.