PROBLEM: It has been well documented that antisperm antibodies can be causative factors of infertility. In this study we have identified an antigen on human sperm surface using serum of an immunoinfertile woman; it is thus a candidate for immunocontraception.
METHOD: Thirty-three women of reproductive age who were infertile were screened for presence of antisperm antibodies by indirect immunofluorescence and agglutination assay. The serum of one such woman, SU-4, reacted with her husband's as well as normal donor sperm and recognized a band of apparent molecular weight of 71-kDa on Western blot. Anti-71 -kDa antiserum was raised in rabbit by eluting 71 -kDa protein and was characterized by agglutination test, immunofluorescence assay, transmission electron microscopy, flow cytometry, and sperm-egg interaction in mouse system.
RESULTS: Interestingly, sera raised in rabbit against 71-kDa antigen, was identified by immunoinfertile serum of SU-4, revealed similar results of localization of human acrosome. Anti-71-kDa antibodies showed cross-reactivity with other species of sperm, demonstrated inhibition of sperm attachment to oocytes in an in vitro mouse system, and revealed surface binding of human live sperm by flow cytometry. Transmission electron microscopy documented the presence of 71-kDa antigen in the acrosomal compartment.
CONCLUSION: This study has put in evidence an antigen of apparent molecular weight of 71-kDa in all donor sperm tested in this study. The presence of this antigen on the sperm of several species will enable us to determine the efficacy of this antigen in controlling fertility in vivo in both rodents and primates. This antigen may be a candidate for immunocontraception.