According to their study, CD4+ CD8+ T cells and CD19+ B cells with PD-1 and PD-L1 expression were found more frequently in women with endometriosis in both early (I/II) and late (III/IV) endometriosis stages, according to the American Society for Reproductive Medicine (ASRM), as compared to healthy individuals. Here, CD4 is linked to endometriosis.