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P671. An IL23R risk variant is associated with changes in CD4+ T-cell subsets in peripheral blood of Crohn's disease patients

T.B. Murdoch1, A. Ueno1, G. Kaplan1, R. Panaccione1, H. Jijon1, M. Silverberg2, C. Hirota1, S. Ghosh1, 1University of Calgary, Division of Gastroenterology, Calgary, Canada, 2University of Toronto, Toronto, Canada

Background

The IL23R locus contains multiple inflammatory bowel disease-associated single nucleotide polymorphisms. IL23R encodes a subunit of the receptor for IL23, a key cytokine in the polarization of the pro-inflammatory Th17 T-cell subset. Previous work has demonstrated that a protective variant in IL23R (A at rs11209026) is associated with a decreased proportion of Th17 cells in peripheral blood. We sought to investigate whether polymorphisms of an intronic SNP in IL23R (rs2201841), which is independently inherited from rs11209026, is associated with changes in the proportion of CD4+ T-cell subsets in peripheral blood of Crohn's disease patients.

Methods

Peripheral venous blood was procured from patients with Crohn's disease (n = 12). DNA was extracted and genotyped for rs2201841 and rs11209026 using the Ilumina OmniExpress platform. Mononuclear cells were isolated from peripheral blood by centrifugation on a Ficoll gradient, and stimulated with PMA and ionomycin in presence of monensin for 15 hours. Cells were stained for CD3, CD4, IL17, IL4, interferon-gamma, and Foxp3, and analyzed by flow cytometry. Data was compared using the Mann–Whitney test, with statistical significance considered at p < 0.05.

Results

The distribution of genotypes at rs2201841 was as follows: CC (n = 2), CT (n = 7), and TT (n = 3). All patients were homozygous for the risk variant (G) at rs11209026. Carriage of the IL23R rs2201841 risk allele (C) was associated with a decreased proportion of IL17+CD4+ T-cells (Th17) in peripheral blood (2.5±1.3% versus 15.3±3.8%, p = 0.036). Carriage of this risk allele was not associated with a significant difference in the proportion of Foxp3+ (Treg), interferon-gamma+ (Th1), or IL4+ (Th2) CD4+ T-cells.

Conclusion

Our preliminary data suggest that the IL23R risk variant at rs2201841 modulates the prevalence of Th17 cells in peripheral blood. Replication in a larger group of patients and healthy volunteers is needed to confirm this finding. Further exploration of the phenotypic and functional influence of IL23R variants on CD4+IL-17+ T-cells will shed light on the role of the IL23/Th17 axis in the pathogenesis of Crohn's disease.