HIGH DIMENSIONAL PROFILING OF REGULATORY T CELLS IN SPONDYLOARTHRITIS REVEALS CELLULAR HETEROGENEITY

Career situation of first and presenting author Student for a master or a PhD Introduction The Spondyloarthritides (SpA) are immune-mediated conditions characterised by spinal and joint inflammation. Numerous studies implicate Th17 lymphocytes in pathogenicity but few reports exist on the role played by regulatory T cells (Tregs) in the disease. Objectives To describe Treg frequency and phenotype in SpA patients compared to controls. To identify differential expression of trafficking molecules and activation markers within Tregs at the inflammatory site. Methods A total of 61 patients with SpA (38 with AS, 23 with PsA) and 16 age-matched healthy controls were recruited. Peripheral blood (PB) and paired synovial fluid (SF) mononuclear cells (n=8) were stained for with 3 multicolor flow cytometry panels, including a total of 35 surface and intracellular protein markers. Manual gating was done in parallel with unsupervised data analysis using FlowSOM and SPADE. Results No difference in PB Treg frequency was observed between SpA and healthy controls. In the SF Tregs were enriched relative to the blood memory (CD45RA-) compartment (mean: 11.7 vs 4.7%; p=0.01) with a higher expression of Foxp3 (p=0.04). The distribution of trafficking markers between patients and controls showed considerable heterogeneity, as visualised on SPADE analysis, but little difference in their relative frequency. Intracellular cytokine staining demonstrated that Tregs from AS and PsA patients have higher potential to secrete IL-17A compared to controls (IL-17A+Tregs mean: 2.8 vs 1.2%; p=0.02). Production of this cytokine overlapped with expression of CD161 and CCR6, both markers associated with Th17. Interestingly, this subset, despite expressing normal levels of Foxp3, expressed lower levels of TIGIT (p=0.04) and Helios (p Conclusions High-dimensional immunoprofiling in SpA patients shows normal frequency of Tregs in the PB, but increased Tregs with activated phenotype in the inflammatory site. The presence of phenotypical markers commonly associated with Th17 in Tregs of non thymic origin are intriguing findings and require further evaluation. References None. Acknowledgements None. Disclosure of Interest D. Simone: None declared, M. H. Al Mossawi Grant/research support from: UCB, I. Brough: None declared, L. Chen: None declared, F. Penkava: None declared, A. Ridley: None declared, H. Shi: None declared, L. Tucker: None declared, N. Yager: None declared, P. Bowness Grant/research support from: Merck, GSK, Celgene.