Identification of an Oolemmal IgG Fc Receptor: Its Role in Promoting Binding of Antibody‐Labelled Human Sperm to Zona‐Free Hamster Eggs

Abstract

Antisperm antibodies (ASAs) present in sera of infertile men and women have been shown either to promote or inhibit penetration of zona-free hamster eggs by antibody-labelled human spermatozoa. Increased numbers of oolemmal-bound sperm have been noted in association with increased sperm penetration frequencies, following antibody labelling, when compared with antibody-free sperm. The promotion of adherence of ASA-labelled sperm to the oolemma could be mediated through the binding of antibodies to common epitopes present on the sperm and egg surfaces or through Fc-mediated binding to an oolemmal Fc receptor. In support of the latter hypothesis, we report that zona-free hamster eggs bind aggregated human IgG and IgG Fc fragments. The presence of an oolemmal IgG Fc receptor has been confirmed using a rat monoclonal antibody (2.4G2) directed against a murine IgG Fc receptor (Fc .gamma. RII) as judged both by indirect immunofluorescence and by immunobead binding. In addition, the pre-incubation of zona-free hamster eggs with IgG Fc diminished both adhesion to and penetration of the oolemma by human spermatozoa.