Interestingly, inverse correlations between the expressions of PD-1 and IFN-γ in the FF CD4+ and CD8+ T cells were found in the infertile patients with PCOS (r2 = 0.418, P < 0.05 and r2 = 0.387, P < 0.05, respectively, Fig. 6c,d). Here, CD4 is linked to polycystic ovary syndrome.