Human Sperm-OocyteInteraction Testing



During natural conception and standard in vitro fertilisation (IVF), motile capacitated sperm with intact acrosomes bind to the surface of the zona pellucida (ZP) and this binding triggers the acrosome reaction (AR). The sperm then passes through the ZP and binds to the oolemma via the plasma membrane that persists over the equatorial segment. The sperm is then engulfed into the ooplasm where decondensation of the nucleus occurs to form the male pronucleus. We have developed tests for human sperm- ZP binding, the ZP-induced AR and spermoolemma binding using oocytes which failed to fertilise in the clinical IVF program. The patients consent to the use of this material for testing or research. Usually the oocytes maintain their ability to bind sperm and stimulate the AR. The ZP can be preserved in concentrated salt solution at 4oC for months. Using these assays we have found defective sperm-ZP binding and disordered ZP-induced AR are common causes of failure of IVF when there are sperm defects, but can also occur with normal semen analysis. These defects of sperm-oocyte interaction could account for about 25% of patients with idiopathic infertility and if diagnosed before IVF is attempted would allow the patients to be treated by ICSI and avoid an IVF cycle with low or zero fertilisation. In contrast, oolemma binding defects appear to be rare. Using experimental conditions in which the amount of ZP was not limiting, we showed that only a small proportion