A monoclonal antibody to a zona pellucida-proteinase inhibitor binding component on murine spermatozoa

A monoclonal antibody, J-23, was produced to an epitope of a binding (acceptor) component on the plasma membrane in the acrosomal cap region of the mouse sperm head. The component binds a proteinase inhibitor of seminal vesicle origin at ejaculation and participates in the in vitro binding of capacitated sperm to the zona pellucida. The antibody, an IgM molecule, recognizes affinity purified acceptor, crude acceptor and whole sperm as determined by ELISA methodology. The antibody reacts with a 15,000 molecular weight component, the size previously determined for the acceptor, found in the supernatants of frozen-thawed cauda epididymal sperm. In addition, it binds to a 21,000 molecular weight component generated by mixing an excess of purified inhibitor (6400 daltons) with a crude acceptor preparation. J-23 binds to an epitope in the same region of the sperm head as does the inhibitor. This epitope becomes fully expressed during epididymal maturation and is found only in the lumen of epididymal tissues. Pretreating sperm with J-23 inhibits their ability to bind the inhibitor as well as the zona pellucida. Pretreating sperm with the inhibitor has little effect on the binding of J-23. These data indicate that J-23 recognizes an epitope on the acceptor but the epitope is not directly involved with inhibitor binding.