Bovine oviduct epithelial cells downregulate phagocytosis of sperm by neutrophils: prostaglandin E2 as a major physiological regulator

This study aimed to investigate the presence of polymorphonuclear neutrophils (PMNs) in bovine oviduct fluid under physiological conditions and to determine the possible role of bovine oviduct epithelial cells (BOECs) in the regulation of the phagocytic activity of PMNs for sperm. During the pre-ovulatory stage, PMNs were identified in the bovine oviduct fluid in relatively constant numbers. In our experiments, PMNs were incubated for 4 h with the supernatant of cultured BOECs stimulated for 24 h by LH (10 ng/ml). Phagocytosis was then assayed by co-incubation of these PMNs with sperm treated to induce capacitation. The BOEC supernatant significantly suppressed sperm phagocytosis by PMNs, and the LH-stimulated BOEC supernatant further suppressed phagocytosis. Importantly, in the BOEC culture, LH stimulated the secretion of prostaglandin E2 (PGE2), which dose-dependently (10 K6 ,1 0 K7 , and 10 K8 M) suppressed sperm phagocytosis by PMNs. Furthermore, a PGEP2 receptor antagonist significantly abrogated the inhibition of phagocytosis by the LH-stimulated BOEC supernatant. Additionally, using scanning electron microscopy, incubation of PMNs with either PGE2 or LH-stimulated BOEC supernatant before phagocytosis was found to prevent the formation of DNA-based neutrophil extracellular traps for sperm entanglement. The results indicate that sperm are exposed to PMNs in the oviduct and PGE2 released into the oviduct fluid after LH stimulation may play a major role in the suppression of the phagocytic activity of PMNs for sperm via interaction with EP2 receptors. Thus, the bovine oviduct provides a PGE2-rich microenvironment to protect sperm from phagocytosis by PMNs, thereby supporting sperm survival in the oviduct.