P093 CCL20 and CCR6 on peripheral blood mononuclear cells (PBMC) in inflammatory bowel disease (IBD): a more potent chemokine in ulcerative colitis?

Abstract Background Chemokines play an important role in the inflammatory process during IBD. CCL20 is a C-C motif chemokine ligand, which has CCR6 as its only receptor. It has been established that CCL20 and CCR6 expression is increased in the mucosa of IBD patients, and we have localised CCL20 to both the epithelium and to mononuclear cells in the lamina propria. Studies on CCL20 and CCR6 in PBMCs from IBD patients conclude that CCL20 is upregulated during active UC, but the mechanisms behind the CCL20 release has not been investigated. In this study we investigated CCL20 and CCR6 in PBMC from IBD patients, and identified innate mechanisms behind CCL20 release from PBMCs. Methods CCL20 was measured in serum from IBD patients and healthy controls by ELISA. PBMCs from 40 subjects; healthy controls (n = 8), active, and inactive ulcerative colitis (UCa and UCi) (n = 16) and active and inactive Crohn’s disease (CDa and CDi) (n = 16), were included in the study. Basal CCL20 and CCR6 gene expression in the PBMCs was measured by qRT-PCR. CD4+, CD8+, CD16+, CD19+, and CD14+ populations, with CCR6+ subpopulations were measured by flow cytometry. CCL20 release from PBMCs following stimulation with ligands to pattern recognition receptors, and IL-1β , TNF, and IL-10 was measured by ELISA. Results Serum CCL20 was significantly increased in UC patients compared with healthy controls. CCL20 gene expression and spontaneous CCL20 release in PBMCs, however, was similar between the groups, indicating that serum CCL20 does not originate mainly from immune cells. UCa patients showed a decreased expression of CCR6 compared with both healthy controls and UCi, which was reflected in a reduced frequency of CCR6+CD4+ cells in UCa. Combined, this indicates a loss of CCR6+CD4+ cells from circulation. Upon stimulation, CCL20 release from PBMCs was particularly increased when activating TLR2/1 or NOD2 and by IL-1β . The TLR2/1- and NOD2-induced CCL20 release was independent on IL-1β. Overall, UC patients had a more potent CCL20 release than CD patients. Conclusions The increase in CCL20 production by immune cells in lamina propria, seems particularly to occur after activation of innate immune receptors. UC patients had the highest levels of CCL20 in serum and the strongest CCL20 response after stimulation, while UCa patients had a lowest CCR6 expression on immune cells. Our findings indicate that the CCL20-CCR6 axis may be more involved in UC than CD.