Cytotoxic sperm antibodies inhibit sperm penetration of zona-free hamster eggs

Zona-free hamster egg sperm penetration assay was used to study the effects of cytotoxic sperm antibodies on egg penetration by the sperm of fertile and infertile men. Twenty-nine fertile and 9 infertile men did not have significant cytotoxic sperm antibodies in their serum and seminal plasma; 7 infertile men were positive for these antibodies in serum and seminal plasma. Two others were positive in sera, and 14 were positive in seminal plasma. Sperm from 18 of 23 (78%) infertile men with sperm antibodies had poor egg penetration (less than or equal to 20%) compared with only 6 of 38 (16%) nonautoimmune men (P less than 0.0001). Sperm from nonautoimmune fertile men were coated with seminal plasma and serum of autoimmune men and serum of isoimmune women, resulting in a significant decrease in hamster egg penetration. Sixteen of 21 (76%) seminal plasma samples with cytotoxic sperm antibodies reduced the control sperm penetration of hamster eggs by greater than or equal to 50%. Coating of sperm from fertile men with serum and seminal plasma samples from non-sperm-immune fertile and infertile subjects did not alter their penetration of hamster eggs. Coating of sperm from autoimmune men with cytotoxic antibody-positive autologous seminal plasma samples resulted in a significant decrease of egg penetration. The inhibitory effect of antibody-positive seminal plasma samples on egg penetration by control sperm was abrogated when the samples were preabsorbed with sperm. It is concluded that cytotoxic sperm antibodies, especially those in seminal plasma, inhibit hamster egg penetration by autologous and control sperm. This may explain in part the incidence of infertility associated with sperm antibodies.