MyD88-dependent TLR pathways regulate B7 co-stimulator expression by stromal cells in the colonic mucosa.

20. HUMEN, M, PINCHUK, I.V., SAADA JI, HOUSE J, JOHNSON, J.R., DANN, S., CONG, Y., POWELL, D.W., & V. E. REYES

Hollywood, Florida

Congreso; Advances in Inflammatory Bowel Diseases. Crohn’s & Colitis Foundation’s. Clinical & Research Conference; 2011

CCFA

MyD88-dependent TLR pathways regulate B7 co-stimulator expression by stromal cells in the colonic mucosa.  Humen Martin, Pinchuk, I.V., Saada JI, House J, Johnson, J.R., Dann, S.,  Cong, Y., ,  Powell, D.W., & V. E. Reyes. Background: Signaling via B7 family co-stimulators is crucial in the antigen presenting cells (APCs)-mediated regulation of T cell activity under mucosal tolerance and in its disregulation leading to inflammatory bowel disease (IBD).  The expression by APCs of Th1 supressing co-stimulator B7-H1 and Th2 promoting co-stimulator B7-H2 (a.k.a ICOSL) is critical in suppression of activated Th1 cell responses during mucosal homeostasis. Human CD90+ stromal cells, a.k.a. myofibroblasts/fibroblasts (CMFs) express  B7-H2 and are major B7-H1 expressing cells in the normal colonic mucosa and, thus, may contribute to the tuning of the Th1/Th2 balance. MyD88-dependent TLR stimulation by microbial ligands is important in the modulation of B7 molecule expression on professional APCs. However, little is known regarding how the expression of B7- costimulators on CMFs is influenced by TLR ligands reaching the mucosal lamina propria during mucosal wound healing  or during IBD  where the epithelial barrier is breached. Our initial data demonstrate  that human normal CMF cultures may upregulate the B7-H1 expression via the MyD88 adaptor involving TLR4 and 5 pathways.  Herein, we extend this study and determine the role of MyD88 involving TLRs pathways in the regulation of B7-H1 and B7-H2 expression in murine CMFs in vitro and in an animal model. Methods: B7 molecule expression on human and murine CMFs  from normal mucosa in response to the bacterial pathogen-associated molecular patterns (PAMPs) was analyzed using real-time RT-PCR and FACS analysis. Confocal microscopy was used to visualize the B7 molecule expression in situ in MyD88-/- and wild type C57BL/6 colonic mucosa. Results: Stimulation of murine CMFs for 24h with ligands for TLR  2, 4 and 5 that signal via the MyD88 adaptor upregulated surface B7-H1 and B7-H2 expression. Similar observations have been made with human CMFs and TLR4 stimulation enhanced these cells suppression of Th1 cells (Tbet and IFN-g expression) in CMF- activated CD4+ T cell co-cultures via a process involving B7-H1. Moreover, the B7-H1 expression on CMFs derived from the colonic mucosa in MyD88-/- mice was lost, but not in CMFs from wild type mice. Conclusion: Our data suggest that TLR pathways  using the MYD88 adaptor might be crucial for the B7-H1 expression on CMFs during mucosal tolerance. Moreover, CMFs play an important role in innate immune responses to bacterial PAMPs and may favor suppression of Th1 type inflammation via upregulation of Th1 suppressing molecule B7-H1 and Th2 promoting  molecule B7-H2. Supported by CCFA, AGA, and NIAID.