Use of oocytes that failed to be fertilized in vitro to study human sperm-oocyte interactions: comparison of sperm-oolemma and sperm-zona pellucida binding, and relationship with results of IVF

Abstract

A test for human sperm binding to the oolemma was developed with oocytes that failed to be fertilized in vitro. The zonae pellucidae of the oocytes were removed under a dissecting microscope by brief exposure to dilute HCl (pH 2.5-3.0) in 0.9% NaCl. The zona-free oocytes (ZFOs) were incubated with a mixture of equal numbers of motile sperm from men to be tested and fertile donors. The sperm was differentially labelled with fluorescein or rhodamine and the results expressed as a ratio of the number of test to control sperm bound to several ZFOs in order to control for variability in the ability of the oolemma to bind sperm. The number of sperm bound to the oolemma increased with time and sperm concentration. The sperm-oolemma binding ratio determined for 32 patients undergoing in vitro fertilization (IVF) was significantly correlated with the sperm-zona pellucida (ZP) binding ratio but was not correlated with other sperm tests. The sperm-oolemma binding ratio was also related to the IVF rate, but this was not significant if the sperm-ZP binding ratio was included in the logistic regression model. Only four of the 32 patients had failure of fertilization in vitro. The human sperm-oolemma binding test may be useful for studying the interaction between gametes, but the test is unlikely to be as useful clinically as the sperm-ZP binding test for predicting fertilization in vitro.