Monoclonal antibodies affecting sperm-zona binding and/or zona-induced acrosome reaction

The majority of anti-sperm monoclonal antibodies which were shown to inhibit in vitro fertilization in our laboratory react with antigens in the acrosomal region of spermatozoa. To elucidate the mechanism of human and/or mouse fertilization inhibition, the effects of these antibodies on mouse sperm-zona binding and mouse zona-induced acrosome reaction in vitro were studied. Among these antibodies, MS-4 and MS-7 were shown to react partially with uncapacitated mouse sperm, and to react more with capacitated mouse sperm, whereas HS-9, HS-11 and HS-63 react only with capacitated and acrosome-intact human or mouse sperm. HS-63 and MS-4 were shown to inhibit zona-induced acrosome reaction significantly, but not the sperm-zona binding. On the other hand, HS-9, HS-11 and MS-7 were shown to inhibit both sperm-zona binding and zona-induced acrosome reaction. The results of this study suggest that fertilization inhibition caused by these antibodies could result from that of the initial sperm-zona binding and/or zona-induced acrosome reaction.