Comparison of the occurrence of spermatozoal antibodies in male and female blood donors.
Sera from 207 male and 190 female blood donors were studied for spermatozoal antibodies by sperm agglutination and indirect IFT on methanol-fixed spermatozoa. 
 
Sperm agglutinins occurred significantly more frequently in men (about 4%) than in women (0·5%), and IFT (with serum diluted 1:10) revealed a similar relation for antibodies against the main tail piece (about 10% in males vs about 3% in females). Antibodies against the front part of the acrosome and against the equatorial segment were, on the other hand, found with the same frequency in men and women, i.e. in 6–7% and 2–3%, respectively. 
 
Antibodies against the front part of the acrosome were predominantly of the IgM class, while staining of the equatorial segment and the main tail piece was mainly caused by IgG antibodies. 
 
The rare occurrence of sperm agglutinins in women may possibly be a consequence of rapid destruction of the corresponding sperm-specific antigens after ejaculation of the spermatozoa. The identical findings in men and women for antibodies against the acrosomal antigens lead to the suggestion that constitutional factors could be of particular importance for the ability to respond to these antigens.