Mo1747 Intestinal IL-10-Producing B Cells Induced by Commensal Bacteria May Contribute to Maintenance of Mucosal Homeostasis

Abstract

Background We demonstrated that wild-type B cells produce Interleukin (IL)-10 following Toll-like receptor (TLR) stimulation and inhibit the production of pro-inflammatory cytokines by T cells and macrophages (MΦ) In Vitro (DDW 2011). However, the In Vivo development and roles of intestinal IL-10-producing B cells in response to gut bacteria are poorly understood. In addition, commensal bacteria have been implicated in the pathogenesis of the inflammatory bowel diseases (IBD) and the regulation of mucosal homeostasis. We hypothesize that commensal microbiota are essential for IL-10 secretion by intestinal B cells.Methods Germ-free (GF) IL-10EGFP reporter (Vert-X) mice were transferred to specific pathogen-free (SPF) conditions and colonized with SPF feces. Mice were studied on days 0, 3 and 7 postcolonization, and populations of IL-10-producing GFP+ cells were analyzed in the colon lamina propria (LP), mesenteric lymph nodes (MLN) and spleen using flow cytometry (FACS) and immunohistochemistry (IHC). To induce chronic colitis, SPF Vert-X mice were cyclically administered 2% dextran sulfate sodium (DSS) solution for 7 day periods. Colonic LP IL10-producing GFP+ cells were identified by FACS.Results 1.5 ± 0.7% of total colonic LP cells in GFVert-Xmicewere GFP+, with the number expanding following bacteria colonization and with chronic inflammation (Table), while those in the spleen and MLN did not significantly change. Of note, the number of GFP+ B cells in the colonic LP greatly expanded following bacterial colonization (1.7-fold from baseline on day 3, and 3.3-fold on day 7, vs. 11.2fold in SPF mice). IHC demonstrated that GFP+ B cells were concentrated in the colonic patches rather than the LP. The ratio of GFP+ colonic Foxp3+CD4+ cells /total GFP+ cells did not change significantly after bacterial colonization (32.6 ± 9.6 % on GF, 32.4 ± 18.9 % on day 3, and 36.8 ± 8.6 % on day 7, vs. 19.7 ± 1.7 % in SPF mice), nor did the numbers of GFP+ MΦ and dendritic cells change. Following chronic DSS administration, the percentage of intestinal GFP+ cells increased (Table). Although CD4+ T cells were predominant among enteric IL-10-producing cells in chronic colitis, the ratio of B cells to total intestinal GFP+ cell increased during chronic inflammation (Table). Summary Commensal bacteria and chronic intestinal inflammation stimulate IL-10 secretion by intestinal B cells, whichmay contribute tomaintainingmucosal homeostasis and help regulate intestinal inflammation. IL-10 producing GFP+ cells in the colonic lymphocytes following bacterial colonization and chronic mucosal inflammation