Sex Difference of Antifertility Effect by Passively Immunized Monoclonal Sperm Antibodies

Sperm‐specific monoclonal antibodies (MS 204, MS 207, HS 11, and HS 63) that had been shown to inhibit fertilization of mouse oocytes in vitro were used to passively immunize male and female mice. In vitro and in vivo fertilization experiments were performed to compare the efficacy of resulting antifertility effects owing to the presence of circulating sperm antibodies. When the sperm from the antibody‐treated mice were recovered for insemination, a partial inhibition of fertilization of mouse oocytes in vitro was observed. However, under the same antibody dose that effectively inhibits the in vivo fertilization of treated female mice the fertilization rate of the treated male was not significantly reduced, when they were mated with normal superovulated females followed by in vitro embryo culture. Similarly, on day 9 after mating with the antibody‐treated males, the number of fetuses in mated females was not significantly different from that of the control. In contrast, when the antibody‐treated females were mated with the proven fertile males, the number of fetuses was significantly reduced in response to the antibody treatment. When I‐125‐labeled monoclonal sperm antibodies were used to passively immunize male mice, the percentage of antibodies recovered from epdidymis (relative to that of blood) was not much different from that of other organs, except for lower percentages detected in brain and testis. In treated females, oviduct and uterus revealed the presence of relatively high percentages of antibodies. Indirect immunofluorescent assay of epididymal sperm recovered from males treated with antibodies of IgG class showed that only a low percentage of sperm were stained immunofluorescently, whereas those from mice treated with IgM antibodies revealed no immunofluorescent staining. The results of this study demonstrated the sex difference in antifertility effect of the passively immunized sperm antibodies. The low antifertility effect of the passively immunized sperm antibodies in males may be attributed to the presence of a blood‐testis and a semipermeable blood‐epididymis barrier, high local sperm concentration, and low effective antibody concentration inside epididymis and vas deferens.