Characterization of a potent sperm-agglutinating monoclonal antibody and its cognate antigens

Abstract

Objective: To identify sperm antigens that are capable of eliciting infertility-related sperm-agglutinating antibodies. Design: In vitro laboratory experiments. Setting: University research laboratory. Patient(s): Fertile semen donors. Intervention(s): None. Main Outcome Measure(s): Sperm agglutination, immunofluorescence localization, and flow cytometric analysis of surface expression of A36 antigens. Antigen analysis by Western immunoblotting. Result(s): Monoclonal antibody A36 induced intensive head-to-head, tail-to-tail, and head-to-tail agglutination of motile human spermatozoa. Antigens recognized by A36 were localized on the acrosomal cap and in the principal tail regions of motile, noncapacitated human sperm. Changes in subcellular levels and localization of the A36-recognized epitope occurred after capacitation and acrosomal loss. A36 reacted with a polymorphic series of proteins in Western blots of sperm extracts from humans and various other animal species, including mouse testis extracts. A common 53-kd antigen was recognized by the antibody in the different antigenic preparations. Conclusion(s): A mouse antibody to human sperm, monoclonal antibody A36, caused intensive agglutination of noncapacitated human spermatozoa and reacted with antigens on the acrosomal cap and in the principal tail regions. Of the multiple polypeptides that were reactive with the monoclonal antibody in sperm extracts from humans and other animal species, a common 53-kd antigen was recognized.