The specificity of human spermatozoa/zona pellucida interaction under hemizona assay conditions

The objective of this prospective study was to evaluate the specificity of human sperm/zona pellucida interaction under hemizona assay (HZA) conditions in experiments with gametes from the same and different species. Human, cynomolgus monkey and hamster oocytes were used after salt-storage. Oocytes were bisected into matching hemizonae by micromanipulation and used in the HZA. Semen was obtained from healthy men (donors) and male cynomolgus monkeys and prepared by wash and swim-up. Sperm binding to matching hemizonae was assessed (tight binding) after 4-h coincubation in the HZA in homologous and interspecies experiments. Acrosome reaction was evaluated in the sperm droplets using FITC-PSA and on the hemizonae using the T-6 monoclonal antibody. On human hemizonae, the number of tightly bound sperm for human and monkey were 93.2 +/- 15.8 and 3.9 +/- 1.3, respectively (P < 0.001). On monkey hemizonae, the number of tightly bound sperm for monkey and human were 126.0 +/- 34.8 and 2.8 +/- 1.6, (P = 0.02) respectively. On hamster hemizonae, there was negligible binding of human and monkey sperm. There was a significantly higher incidence of acrosome reacted sperm on the zona pellucida in homologous compared to heterologous experiments. These results demonstrate a high species-specificity of human gamete functions under HZA conditions, providing further support for the use of this bioassay in infertility and contraception testing.