Background & Aims: Dendritic cells (DCs) possess the most potent ability to induce acquired immunity. However, their involvement in the pathogenesis of Crohn's disease (CD) has not yet been determined. We aimed to establish the immune status of mesenteric lymph nodes, the major gut-associated lymphoid tissue, and isolated DCs and determine their involvement in the pathogenesis of CD. Methods: CD4+ T cells and DCs were isolated from mesenteric lymph nodes of CD, ulcerative colitis, and normal control. The immune status of CD4+ T cells was analyzed by cytokine production and transcriptional profile. Surface phenotype of DCs was analyzed by flow cytometry. Cytokine production by myeloid DCs was analyzed by real-time polymerase chain reaction and exogenous bacterial stimulation. Immune stimulating activity of DCs was determined by mixed lymphocyte reaction. Results: In CD, mesenteric lymph node CD4+ T cells produced higher amounts of interferon-γ and interleukin (IL)-17 compared with ulcerative colitis and normal control, and this was dictated by increased T-bet and retinoic acid-related orphan receptor-γ expression. Three subtypes of DCs, myeloid DC, plasmacytoid DC, and mature DC, were identified in all groups. When stimulated with exogenous bacterial derivative, myeloid DCs from CD produced a higher amount of IL-23 and a lower amount of IL-10. Myeloid DCs from CD induced stronger T helper cell (Th)1 immune response in mixed lymphocyte reaction compared with those from ulcerative colitis and normal control. Conclusions: Our findings revealed that mesenteric lymph node is the key pathogenic location of CD elicited by the unique cytokine milieu produced by DCs leading to a dysregulated Th1/Th17 immune response.
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