Effect of Antisperm Antibodies Present in Human Follicular Fluid upon the Acrosome Reaction and Sperm-Zona pellucida Interaction

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.