Ovulatory follicular fluid induces sperm phagocytosis by neutrophils,

What is it about?

We have recently shown that the conditioned media from bovine oviductal epithelial cell culture suppress sperm phagocytosis by neutrophils, suggesting that the oviduct around oestrus supplies the anti‐inflammatory microenvironment. To investigate the immune response of neutrophils toward the sperm at ovulation in the buffalo oviduct, we examined (a) a detailed distribution of neutrophils in the oviduct in buffaloes, (b) the effect of ovulatory follicular fluid (FF) and oviductal fluid (OF) on sperm phagocytosis by neutrophils, and (c) the interaction of the ovulatory FF with OF on sperm phagocytosis by neutrophils in vitro. Buffalo oviducts were collected from healthy reproductive tracts at a local slaughterhouse. A detailed observation by histological examination and transmission electron microscopy revealed that neutrophils exist in the oviduct epithelium and lumen throughout the oestrous cycle in buffaloes. The number of neutrophils at the oestrus stage was higher in ampulla compared with those in isthmus, whereas they remained relatively constant at the dioestrus stage. Two hours of preincubation of neutrophils with FF enhanced sperm phagocytosis through the formation of neutrophil extracellular traps (NETs) together with H2O2 production, whereas OF around oestrus (eOF) suppressed sperm phagocytosis, NETs formation, and H2O2 production and relieved the above FFinduced inflammatory response. Our findings show that neutrophils exist in the healthy cyclic oviduct across bovine species, and the OF supplies a strong anti inflammatory environment that could minimize the inflammatory effect of the FF that flows into the oviduct lumen after ovulation and supports the occurrence of fertilization

Featured Image

Why is it important?

In conclusion, the findings of the present study suggest that the preovulatory oviduct fluid suppresses sperm phagocytosis by neutrophils via reduction of NETs formation and H2O2 production in the buffalo oviduct. Moreover, the oviduct fluid strongly decreases the inflammatory effect of FF that should flow into the oviduct lumen following ovulation. Altogether, it is proposed that the preovulatory oviduct fluid plays a strong anti‐inflammatory role against sperm phagocytosis by neutrophils, which overcomes the proinflammatory effect of ovulated FF. Thus, our data support the hypothesis that the preovulatory oviduct fluid coordinates the immune environment in the buffalo oviduct for supporting the occurrence of fertilization.

Perspectives