The CD4+/PD-1 : CD4+/PD-L1+ T cell ratio was lower in the endometriosis group (1.84 ± 1.23, median 1.45, Min–Max 0.57–6.26) than in the healthy subjects (3.1 ± 1.2, median 2.83, Min–Max 3.1 ± 1.2) (p < 0.0001). Here, CD4 is linked to endometriosis.