Engulfment of spermatozoa by cumulus cells and the role of CD36

The function of cumulus cells after sperm penetration is not well understood. The present study examined the phagocytic action of cumulus cells on sperm after dispersion of cumulus–oocyte complexes. In a co-incubation system of cauda sperm and cumulus cells, the sperm heads were beginning to vanish after 2.5 h and 77% ± 1.34 of sperm heads had disappeared at 30 h. Most of the sperm heads were engulfed by cumulus cells. Immunofluorescent studies showed that cumulus cells were expressing the CD36 molecule, and sperm were exposing phosphatidylserine (PS). Anti-CD36 antibody and annexin V inhibited the engulfment of sperm by cumulus cells by 26.0% and 40.5%, respectively. These results suggested that the cumulus cells recognized the PS molecules on sperm via CD36 and this molecular interaction possibly triggered the phagocytosis of sperm by cumulus cells. These results suggest that cumulus cells might play a role in inhibiting undesired immune reactions induced by sperm antigens.