SPERM-ZONA PELLUCIDA BINDING OF HUMAN SPERM IS CORRELATED WITH THE IMMUNOCYTOCHEMICAL PRESENCE OF PROACROSIN AND ACROSIN IN THE SPERM HEADSBUT NOT WITH THE PROTEOLYTIC ACTIVITY OF ACROSIN

Objective: To determine whether the sperm-zona pellucida (ZP) binding is related to the presence of immunoreactivity for proacrosin and acro sin and/or to the proteolytic activity of acrosin. Setting: The Androl ogy Clinic, University of L'Aquila, Italy. Patients: Thirty-five infer tile couples and 15 men of proven fertility. Interventions: Salt-store d unfertilized oocytes after IVF were inseminated with a mixture of eq ual numbers of test and fertile donor sperm after swim-up selection, r espectively labeled with fluorescein or rhodamine. Total acrosin activ ity, the percent of sperm immunostained for proacrosin and acrosin, an d the percent of sperm with oval heads were evaluated in fresh semen a nd after swim-up selection. Main Outcome Measures: Three zonae were us ed for each patient and sperm-ZP binding ratio (ZP ratio) was calculat ed as the total number of test sperm bound to ZP divided by the total number of control sperm bound to ZP. The ZP ratio was compared with th e percent of live sperm immuno-stained for proacrosin and acrosin, wit h total acrosin activity and with the percent of sperm with oval heads after swim-up selection. Results: The sperm-ZP binding ratio was corr elated positively with the percent of sperm immunostained for proacros in and acrosin and with the percent of sperm with oval heads, but not with acrosin activity. Ejaculates with immunostaining for proacrosin a nd acrosin greater than or equal to 55% of sperm (the mean value of in fertile couples) and acrosin activity < 24 mu IU/10(6) sperm (the mean value of infertile couples) (n = 8) had a ZP ratio greater than or eq ual to 0.5, whereas ejaculates with low immunostaining for proacrosin and low acrosin activity (n = 12) had a ZP ratio < 0.5. The difference between the ZP ratio of the two groups was highly significant. Conclu sions: The ZP binding is related to the immunocytochemical presence of proacrosin and acrosin but not to the proteolytic activity of acrosin in human sperm, suggesting that egg recognition and proteolytic activ ity are independent functions of proacrosin and acrosin.