Antisperm antibodies induce polyspermy by promoting adherence of human sperm to zona-free hamster eggs

Certain antisperm antibodies (ASAs) in the sera of infertile men or women promote the penetration of zona-free hamster eggs by spermatozoa. We have shown previously that this enhancement of penetration occurs through mechanisms other than an alteration in the acrosomal structure of antibody-labelled spermatozoa. In the present study, small limited populations of antibody-labelled and antibody-free spermatozoa from fertile donors were observed serially by phase contrast, epifluorescence and scanning electron microscopy following their adherence to the oolemma of zona-free hamster eggs. The adherence of ASA-labelled spermatozoa to the zona-free hamster egg was markedly increased and occurred earlier when compared with antibody-free spermatozoa from the same ejaculate. The likelihood of entry of an antibody-labelled spermatozoon into the ooplasm, however, once adherent to the oolemma was not different to that of an antibody-free spermatozoa, and the ultrastructural steps of incorporation of antibody-labelled human spermatozoa were also similar to those observed during fertilization of hamster eggs by spermatozoa of several other species. These observations indicate that ASAs promote polyspermic fertilization of zona-free hamster eggs primarily through their enhancement of sperm--oolemmal binding.