Evidence for the synthesis and secretion of a CBG-like serpin by human cumulus oophorus and fallopian tubes

The acrosome reaction (AR)-inducing effect of follicular cells, like that of the cumulus oophorus and granulosa cells, has been described previously. In addition to the well known steroid secreting activity of cumulus cells, the results obtained here demonstrate the secretion of a corticosteroid-binding globulin (CBG)-like protein. An AR-inducing effect was shown with the culture medium of human cumulus oophorus. This effect could be eliminated by treating the sample with monoclonal antibodies against CBG. Moreover, Western blotting after SDS-PAGE of the culture medium strongly indicates that human cumulus cells actively express and secrete a CBG-like protein. This might give an indication as to the origin of the acrosome reaction-inducing substance found in follicular fluid. Furthermore, AR-inducing activity and the elimination of this activity by antibodies against CBG was shown for oviductal fluid. With immunohistochemical techniques the CBG-like protein was localized in the epithelial lining of the fallopian tubes, giving possible evidence for the involvement of this molecule in fallopian tube function.