A human sperm antigen possibly involved in binding and/or fusion with zona-free hamster eggs

A monoclonal antibody to human sperm (MH61) was established. The antibody did not attach to ejaculated sperm but to a head region of some sperm that was incubated in medium for 4 to 12 hours. A23187 treatment significantly increased the number of sperm that were reactive to the antibody. When sperm that bound to the zona-free hamster egg were subjected to the indirect immunofluorescence staining, all the sperm reacted to MH61 with their entire head region. The addition of the antibody to the medium before sperm addition reduced the fusion rate of human sperm to zona-free hamster egg.