Identification of sperm antigens that regulate fertility

Polyclonal antisera were generated in rabbits against human sperm extracts. Out of many such antisera, one was selected (antiserum I) because it recognized relatively few antigens on Western blots. Antiserum I identified immunostainable material on the acrosome of human, monkey, rabbit, hamster, rat and mouse sperm. A detailed histochemical study using rat testes showed that the antigen was detectable on early spermatids and sperm, but not on less mature germ cells. Immunohistochemistry at the electron microscope level localized the antigen on the plasma membrane of rat sperm. In Western blots using human sperm extracts, the antibody recognized a major band with an apparent molecular weight (MW) of 40,000 and minor bands at 43,000 and 72,000. With extracts of monkey sperm and rat testicular cytosol, antiserum I recognized antigens of 69,000 and 23-24,000, respectively. Functionally, antiserum I produced strong agglutination of human sperm. It also prevented attachment of mouse sperm to mouse oocytes in vitro and reduced fertility when administered to female mice. These results suggest that antiserum I can be used as a possible reagent for selecting sperm antigens as components of a contraceptive vaccine.