Interference of antisperm antibodies with the induction of the acrosome reaction by zona pellucida (ZP) and its relationship with the inhibition of ZP binding

Objective: To determine whether antisperm antibodies can interfere with the induction of the acrosome reaction (AR) by the zona pellucida (ZP) and whether this interference also can occur in the absence of an inhibitory effect on ZP binding. Design: Prospective in vitro study. Setting: A tertiary care center, the Andrologic Clinic, University of L'Aquila. Patient(s): Sera from 12 infertile patients with high titers of circulating antibodies directed against the sperm head were studied. Intervention: None Main Outcome Measure(s): The effect of antisperm antibodies on ZP binding was evaluated by matching antibody-exposed and nonexposed donor sperm suspensions labeled with fluorescein or rhodamine, respectively, and incubated with the same salt-stored human ZPs. The effect of antibodies on ZP-induced AR was determined by challenging antibody-exposed and nonexposed donor sperm suspensions with human ZPs disaggregated with acidic NaH2PO4. Acrosomal status was evaluated using fluorescein-labeled Pisum sativum agglutinin and supravital stain Hoechst 33258. In some selected cases, the effect of antisperm antibodies on the acrosomal status of sperm bound to intact ZP also was evaluated using transmission electron microscopy. Result(s): Five of 12 sera exhibited an inhibitory effect on ZP binding. An inhibition of AR induction by disaggregated ZPs (ranging from 64% to 98%) was produced by all 5 sera with an inhibitory effect on ZP binding and by 2 of 7 sera without an inhibitory effect on ZP binding. The different effects of antisperm antibodies on AR induction by disaggregated ZP were confirmed by comparing with ultrastructural evaluations on the acrosomal status of sperm bound to intact ZP. Conclusion(s): Antisperm antibodies can interfere with the induction of AR by ZP. This inhibition can occur even in the absence of an inhibitory effect on ZP binding. Neither effect may occur. (C) 1997 by American Society for Reproductive Medicine.