Su2065 Peripheral Blood Monocyte/Macrophage Maturation Phenotype in IBS After Stimulation With LPS

Background: IBS pathophysiology remains poorly understood; however, recent findings support a state of immune activation characterized by increased TLR expression and intestinal epithelial diffusion of bacterial molecules in the gut, at least in a subgroup of patients. Aims: We sought to relate these factors in IBS, by analyzing the maturation phenotype of peripheral blood monocyte/macrophage cells, according to the intestinal maturation-process [M1: initial stage (CD11c+CD206-), M2: advanced maturation (CD11c-CD206+CX3CR1+)] when stimulated with E. coli-Lipopolysaccharides (LPS). Methods: 21 IBS-Rome II patients and 19 controls were studied in Mexico City. Isolated peripheral blood mononuclear cells (PBMCs) were cultured for 72 hours with and without E. Coli-LPS, and the polarization phenotype of monocytes/macrophages (CD14+) was investigated by flow cytometry. Also, levels of Transforming Growth Factor-beta 1 (TGF-β1), a M2 cell-derived cytokine involved in tissue healing, was investigated by enzyme-linked immunosorbent assay (ELISA), in culture's supernatant. TheMann-Whitney U-test was used, considering a p<0.05 as significant. Results: LPS-stimulated CD14+ cells displayed lower CD11c expression levels in both IBS patients and controls than in the unstimulated condition (8766±730.2 vs 12920±949.2, p<0.001 and 8233±613.9 vs 13750±743.3, p<0.001; respectively), but there were no differences between the IBS and controls. Also, M1 (CD11c+CD206-) unstimulated cells showed lower CD11c expression in IBS vs controls (11540±537.5 vs 13860±893.7, p=0.038); while a decrease in both IBS (11540±537.5 vs 7940±537.7, p<0.001) and controls (13860±893.7 vs 8091±574.5, p<0.001) was observed after LPS-stimulation. In addition the percentage of CD11c+CD206+CX3CR1+ cells was higher in IBS vs controls (9.5±1.5% vs 4.9±1.4%) without LPS stimulation. When comparing the unstimulated vs LPS-stimulated condition, the CX3CR1 expression level in M2-cells increased in controls but not in IBS (71.1±89.5 vs -151.7±31.1, p<0.001). Finally, no differences were observed in TGF-β1 levels of both IBS vs controls (3.77±0.39 vs 3.61±0.14), even after stimulation with LPS (3.58±0.18 vs 3.57±0.13). Conclusions: The data suggests that the initial phase of maturation of monocytes/ macrophages is faster in IBS vs controls. However, the absence of an increase in CX3CR1 expression in response to LPS in IBS, suggests an altered immnoregulatory response in patients with this disorder. Nevertheless, lack of differences in TGF-β1 between the IBS and controls supports the hypothesis that CD11c-CD206+ CX3CR1+ cells in IBS are not related to a healing response but to altered immunoregulatory functions in the presence of PAMPs. Funded by grant PAPIIT IN210010, DGAPA-Universidad Nacional Autonoma de Mexico (UNAM). Oscar Rodriguez-Fandino was funded by grant CONACyT No. 336205.