As shown in Fig. 4a,b, the expression of PD-1 on CD4+ T cells in the PCOS group with infertility was significantly higher than that in the control group (13.80% ± 3.18% vs. 26.13% ± 3.31%, P < 0.05; 10.31% ± 2.34% vs. 19.30% ± 2.50%, P < 0.01). Here, CD4 is linked to polycystic ovary syndrome.