CD4 and pulmonary tuberculosis: In the current study, we explored PD-1/PD-L1 expression on CD4+CD25+CD127low Tregs among active pulmonary TB patients, and we found the negative signal of PD-1/PD-L1 was an important factor controlling the proliferation of Tregs, and its downregulation in Tregs contributed to the proliferation of Tregs.