• Acrosome reaction;
  • antisperm antibodies;
  • follicular fluid;
  • spermatozoa;
  • zona pellucida

Problem: To determine the ability of IgGs isolated from follicular fluids (hFFIgGs) to induce the acrosome reaction (AR) in human spermatozoa and to inhibit sperm–zona pellucida (ZP) interaction.

Method of study: Incubation of capacitated spermatozoa with hFFIgGs (n = 40) and assessment of their effect on the AR or hemizona (HZ) assay in a condition that allows sperm–ZP interaction, avoiding acrosomal exocytosis.

Results: hFFIgGs from different women varied in their ability of inducing the AR. Those hFFIgGs with the highest AR-inducing capacity evoked the exocytotic response in most of the different sperm donors tested [high Induction Frequency (IF)]. Some of these antibodies were also able of inhibiting sperm binding to ZP [low HZ Index (HZI)]. A significant correlation was found between the IF and the HZI for each hFFIgG.

Conclusions: Human follicular fluid contains antibodies capable of inducing the AR and inhibiting sperm–ZP binding, suggesting that they could be directed towards ZP receptors. hFFIgGs would constitute a tool for the identification of sperm entities involved in fertilization.