Dysfunction of peripheral regulatory T cells predicts lung injury after cardiopulmonary bypass

Lung injury caused by cardiopulmonary bypass (CPB) increases the mortality after cardiac surgery. Previous studies have shown that regulatory T cells (Tregs) play a protective role during CPB, but the correlation between Tregs and CPB-induced lung injury remains unclear. Here, we conducted a prospective study about Treg cells in patient receiving CPB. Treg cells were collected from patients before the CPB operation (pre-CPB Tregs), and the effect of pre-CPB Tregs on the occurrence of CPB-induced lung injury was evaluated. Data showed that the baseline level of Treg cells in peripheral blood were lower in patients who developed lung injury after CPB, compared to those who did not develop lung injury after CPB. Function analyses revealed that pre-CPB Tregs from CPB-induced lung injury patients presented decreased ability in suppressing the proliferation and IFN-γ production of CD4 and CD8 T cell. Also, pre-surgery levels of TGF- β and IL-10 were markedly lower in lung injury patients than in non-lung injury patients. In addition, PD-1 and Tim-3 expression on pre-CPB Tregs were significantly lower in CPB-induced lung injury patients than the CPB patients without lung injury. Above all, we found impaired peripheral Treg responses in CPB-induced lung injury patients, indicating a potential role of Treg cells in the early diagnosis of CPB-induced lung injury.