The proportions of naive B cells (P < 0.001), plasma cells (P = 0.012), CD8+ T cells (P = 0.013), follicular helper T cells (P < 0.001), regulatory T cells (Tregs) (P = 0.004), resting NK cells (P = 0.037), and activated NK cells (P < 0.001) in endometriosis tissues were significantly lower than those in control tissues. Here, CD8A is linked to endometriosis.