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* = Presenting author

P059 Mucosal inflammation promotes activation of circulating Vδ2+ T-cells in Crohn's disease

McCarthy N.*1, Gordon H.1, Rahman S.1, Harrow P.1,2, Stagg A.1, Lindsay J.1,2

1The Blizard Institute, Queen Mary University of London, Centre for Immunobiology, London, United Kingdom 2Barts Health NHS Trust, Department of Gastroenterology, London, United Kingdom

Background

Phosphoantigen-responsive lymphocytes (Vδ2T-cells) are absent in rodent models but common in human blood, where they mediate host protection against tumour cells and bacteria. In health, activated Vδ2T-cells traffic to mucosal tissues and contribute to epithelial barrier protection, whereas in Crohn's disease (CD) these cells promote intestinal inflammation via enhanced expression of TNFα. Microbial activation increases Vδ2T-cell sensitivity to azathioprine (AZA) in vitro, and routine AZA therapy selectively ablates Vδ2T-cells in CD patients in vivo, but the factors that influence drug susceptibility of circulating Vδ2T-cells are unknown. We assessed whether the AZA sensitivity of blood Vδ2T-cells in CD patients can be attributed to release of stimulatory factors from the inflamed mucosa into the peripheral circulation.

Methods

Peripheral blood was subjected to density gradient separation of mononuclear cells (PBMC) or directly labelled with monoclonal antibodies for phenotypic analysis of circulating Vδ2T-cells by flow cytometry. PBMC were cultured with/without microbial phosphoantigen in the presence or absence of blood plasma from CD patients or healthy controls to assess Vδ2T-cell stimulatory/suppressive potential of circulating soluble factors. T-cell phenotype, proliferative capacity, and gut-homing potential were assessed by flow-cytometry.

Results

Blood Vδ2T-cells were selectively ablated in CD patients receiving routine AZA therapy but only moderately reduced in a control group of patients receiving the same treatment regimen (2mg/kg/day) for Behçet's disease without gut involvement, suggesting that mucosal inflammatory activity influences peripheral stimulation and loss of Vδ2T-cells. Consistent with this concept, blood Vδ2T-cells from CD patients displayed significantly reduced expression of the inhibitory cell surface receptor PD-1 in active disease (CRP >5mg/L). Microbial stimulation of healthy control Vδ2T-cells in the presence of human blood plasma stimulated marked proliferation and upregulation of MHC class II and gut-homing integrin β7. However, while healthy plasma restrained PD-1 upregulation by control Vδ2T-cells, blood plasma from CD patients enhanced PD-1 expression and supported further upregulation of this molecule upon microbial activation in vitro. These data suggest that CD plasma contains stimulatory factors that induce differential activation of blood Vδ2T-cells in health and disease.

Conclusion

Activation of gut-tropic Vδ2T-cells in the blood of CD patients is influenced by mucosal disease activity and may be enhanced by translocation of phosphoantigen and/or release of pro-inflammatory mediators into the circulation.