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Inhibition of fertility and sperm-zona binding by antiserum to the rabbit sperm membrane autoantigen RSA-1.

Specific antiserum to the rabbit sperm membrane autoantigen (RSA-1) was used to study the role of RSA-1 during fertilization. Artificial insemination of rabbits with spermatozoa treated with anti-RSA-1 Fab resulted in a 68% decrease in the number of fetuses. In vitro, sperm-zona binding was reduced (62%) and penetration completely inhibited by the specific Fab antibodies. Immunofluorescent localization of RSA-1 during fertilization showed that the postacrosomal fluorescence of the spermatozoon was lost on spermatozoa bound to the zona peliucida or penetrating it, if the acrosome reaction had occurred. Spermatozoa swimming in the perivitelline space also did not fluoresce. It is concluded that penetration and binding are independent events which may involve different but perhaps overlapping subsets of sperm surface components and that RSA-1 plays an important role during the penetration of the spermatozoon through the zona pellucida.