Abstract 312: Frequencies and Functional Characterization of Regulatory T Cell Subsets in Patients with Coronary Artery Disease

Abstract

Background: There is evidence for a protective role of regulatory T cells (Tregs) in atherosclerosis. A few studies have analysed Tregs in patients with coronary artery disease (CAD) although with contradictory results. Our aim was to characterize naïve(n) Tregs and memory(m) Tregs in patients with CAD. Methods: Phenotypic analysis of circulating Tregs (including activation markers CTLA4 and Helios) was performed in 21 patients with CAD (all statin-treated) and 24 controls by flow cytometry. CD4+ T cells were enriched by negative selection followed by positive selection using anti-CD4, anti-CD25, anti-CD127, and anti-CD45RA. The fractions of CD4+CD25highCD127lowCD45RA- (mTregs) and CD4+CD25highCD127lowCD45RA+ (nTregs) were analysed for FoxP3 expression. In suppression assays, nTregs and mTregs were cocultured with T responder cells (CD4+CD25-CD127+) at ratios of 1:1, 1:4 and 1:10 for 18 h. Proliferation was evaluated by using a BrdU assay. Results: Total Tregs were reduced in patients compared with controls, 3.8 (3.2-4.7) % vs 4.8 (4.0-5.4) %), p=0.011. Patients also had lower proportions of nTregs, 1.0 (1.0-1.3) % vs 1.4 (1.1-2.0) %, p=0.015, compared with controls while the difference in mTregs did not reach significance, 2.6 (2.0-3.3) % vs 3.0 (2.3-3.2) %. The expression of FoxP3+ in nTregs tended to be reduced in patients compared with controls (77 % vs 88 %, p=0.06) while its expression in mTregs was significantly decreased in patients compared with controls (83 % vs 90 %, p=0.015). The expression of CTLA4 and Helios was significantly higher in mTregs than nTregs in vivo but did not differ between patients and controls. However, the ability of Tregs, in particular nTregs, to inhibit responder CD4+CD25- T cell proliferation at a 1:1 ratio was significantly reduced in patients, p<0.001. Conclusion: The proportions of Tregs as well as FoxP3 expression in Tregs were reduced in CAD patients. Moreover, the suppressive capacity of nTregs was markedly impaired in patients although the expression of activation markers on Tregs in vivo did not seem to reflect the suppressive capacity ex vivo. The data highlight the presence of immune perturbations in CAD and call for further studies to evaluate clinical consequences involving immune dysfunction.