Compartmentalized expression of Th1 and Th17 cytokines in pediatric inflammatory bowel diseases.

BACKGROUND: Interleukin (IL)-23, IL-17A, IL-17F, and interferon-gamma (IFN-γ) are important mediators of inflammatory colitis and are potential therapeutic targets in inflammatory bowel disease (IBD). Their expression profile in the different parts of normal noninflammatory intestine is unclear and their changes during pathology have not yet been addressed in pediatric IBD patients.
METHODS: We quantified the transcriptional expression of IL-23, IL-12, IL-17A, IL-17F, IL-6, and IL-10 in healthy, noninflammatory duodenum, ileum, and colon and in inflamed and noninflamed biopsies of pediatric patients with Crohn's disease (CD) and ulcerative colitis (UC).
RESULTS: In healthy tissue, expression of IL-17A is highest in the ileum, with IFN-γ expression lowest in the colon. Compared to healthy sections, CD patients displayed increased IL-12p35 and IFN-γ levels in noninflamed ileum and colon, respectively. Modifications of cytokine expression between noninflamed and inflamed tissues was characterized by increased IL-17A in UC colon, IFN-γ in CD colon, and IL-17A, IFN-γ and IL-6 in CD ileum. Elevated IL-17A levels were positively correlated with IFN-γ in both inflammatory CD and UC but IL-17A and IFN-γ were correlated with IL-23p19 in CD ileum only.
CONCLUSIONS: The expression of Th1 and Th17 cytokines varies along the intestine, indicating local specific regulation mechanisms. However, the cytokine expression patterns in the same tissue depends on the pathology, with a Th1 or a Th17 profile in the colon of CD and UC patients, respectively, and a Th1/Th17 profile in the ileum of CD patients. This indicates overlapping but distinct immune mechanisms driving intestinal inflammation in these two pathologies.