Overexpression of programmed cell death-1 and human leucocyte antigen-DR on circulatory regulatory T cells in out-of-hospital cardiac arrest patients in the early period after return of spontaneous circulation

Aim: Whether regulatory T cells (Tregs) are involved in immune disorders of out-of-hospital cardiac arrest (OHCA) patients after return of spontaneous circulation (ROSC) is still unknown. We aimed to observe the expression of circulatory Tregs in OHCA patients and investigate programmed cell death-1 (PD-1) and human leucocyte antigen-DR (HLA-DR) on Tregs to evaluate the induction and activity of Tregs. Methods: Sixty-seven consecutive OHCA patients who recovered from spontaneous circulation over 12 h were enrolled. Clinical and 28-day outcome data were collected. Peripheral blood samples collected on days 1 and 3 after ROSC were analysed to evaluate PD-1 and HLA-DR expression on Tregs. Fifty healthy individuals were enrolled as healthy controls. Results: Compared with those in healthy individuals, circulatory Treg counts significantly decreased without changes of Treg/cluster-of-differentiation (CD) 4+ lymphocyte ratios on day 1 after ROSC, and the percentage of PD-1+ Tregs and HLA-DR+ Tregs significantly rose. On day 3, Treg/CD4+ lymphocyte ratios rose with persistently low Treg counts, and the expression of PD-1 and HLA-DR on Tregs was not different from that on day 1. On day 1, both circulatory Treg counts and Treg/CD4+ lymphocyte ratios in non-survivors were lower than those in survivors, and Treg/CD4+ lymphocyte ratios increased in non-survivors on day 3. No significant difference of PD-1 and HLA-DR expression on Tregs was found between survivors and non-survivors on day 1. Conclusions: After ROSC, despite decreased circulatory Treg counts, a relative increase of Treg percentage and enhanced activity of Tregs are involved in early immune regulation of OHCA patients.