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 FF‐
induced 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.