The frequencies of CD8+/PD-1+ T cells in patients with endometriosis stages I and II (8.19 ± 3.76%, median 7.59%, Min–Max 1.90–15.48%) and III and IV (10.40 ± 3.11%, median 8.81%, Min–Max 7.83–16.45%) exceeded those of the healthy subjects (3.60 ± 1.46%, median 3.71%, Min–Max 1.36–6.17%) (Figure 2(b)). Here, PDCD1 is linked to endometriosis.