W1791 Abnormal Response to Commensal by Intestinal Macrophages Play the Central Roles for Pathogenesis of Crohn's Disease

Abstract

Background & Aim: One of the most important concepts of IBD pathophysiology is that the homeostasis of gut immune system to enteric flora becomes discordant. Intestinal macrophage is a key player for not only elimination of bacteria by phagocytosis, but also intestinal immune homeostasis. We have presented about a functional role of intestinal macrophages for gut homeostasis and that disreguration of intestinal macrophages to commensal lead to chronic intestinal inflammation in Crohn's disease. Materials & Methoods: lamina propria mononuclear cells (LPMCs) were isolated according to the protocol previously established. CD14+ intestinal MΦs were isolated by EasySep Human CD14+. CD4+ T cells were isolated from PBMCs and LPMCs. For the study of APC function of CD14+ macrophages, mixed lymphocyte reaction with naive CD4+ T cells was performed and differentiation, proliferation, and cytokine production were examined. For the study of local immune response, isolated CD14+ MΦs or LPMCs were stimulated by whole bacteria antigen (heat killed Enterococcus feacalis). TL1A mRNA transcription by intestinal MΦs with or without bacteria stimulation was analyzed by quantitative RT-PCR. The effect of TL1A and IL-23 on cytokine production by T cells was analyzed by CBA and flow cytometry. Results: We identified that number of CD14+CD33+CD68+ unique intestinal MΦs increased in LP in the patients with IBD, especially Crohn's disease. These cells showed typical MΦs morphology, but they also expressed some DC markers and they had antigen presenting function. CD14+ intestinal MΦs induced both Th1 and Th17 cells from peripheral blood naive T cells. Intestinal bacteria enhanced Th17 polarization by IL-1β and IL-6 produced by CD14+ intestinal MΦs ,while IL23 enhanced Th1 immunity. Thus, CD14+ intestinalMΦs may involved in the pathogenesis of Crohn's disease as APCs. In local immunity, these intestinal MΦs produced large amount of TNFα and IL-23, which are key cytokines for Crohn's disease pathogenesis, in response to commensal bacteria. IL-23 enhanced production of IFNγ by lamina propria mononuclear cells. We identified that source of IFNγ are CD4, CD8 T cells and mucosal natural killer cells. In addition, TL1A cooperating IL-23 synergistically may enhance IFNγ and IL-17 production by lamina propria CD4+ T cells. Conclusion: CD14+ intestinal MΦs play the central roles in the pathogenesis of Crohn's disease by regulating local immunity and inducing both Th1 and Th17 immunity by APCs.