Decreased frequencies and impaired functions of the CD31 + subpopulation in T reg cells associated with decreased FoxP3 expression and enhanced T reg cell defects in patients with coronary heart disease

Summary Coronary heart disease (CHD) is one of the most common types of organ lesions caused by atherosclerosis, in which CD4 + CD25 + forkhead box protein 3 (FoxP3 + ) regulatory T cells (T reg ) play an atheroprotective role. However, T reg cell numbers are decreased and their functions are impaired in atherosclerosis; the underlying mechanisms remain unclear. CD31 plays an important part in T cell response and contributes to maintaining T cell tolerance. The immunomodulatory effects of CD31 are also implicated in atherosclerosis. In this study, we found that decreased frequencies of the CD31 + subpopulation in T reg cells (CD31 + Tr cells) correlated positively with decreased FoxP3 expression in CHD patients. Cell culture in vitro demonstrated CD31 + Tr cells maintaining stable FoxP3 expression after activation and exhibited enhanced proliferation and immunosuppression compared with the CD31 − subpopulation in T reg cells (CD31 − Tr cells). We also confirmed impaired secretion of transforming growth factor (TGF)‐β1 and interleukin (IL)‐10 in CD31 + Tr cells of CHD patients. Further analysis revealed reduced phospho‐SHP2 (associated with CD31 activation) and phospho‐signal transducer and activator of transcription‐5 (STAT‐5) (associated with FoxP3 transcription) levels in CD31 + Tr cells of CHD patients, suggesting that decreased FoxP3 expression in CD31 + Tr cells might be because of attenuated SHP2 and STAT‐5 activation. These data indicate that decreased frequencies and impaired functions of the CD31 + Tr subpopulation associated with decreased FoxP3 expression give rise, at least in part, to T reg cell defects in CHD patients. Our findings emphasize the important role of the CD31 + Tr subpopulation in maintaining T reg cell normal function and may provide a novel explanation for impaired immunoregulation of T reg cells in CHD.