Characterization of a sperm-specific monoclonal antibody and isolation of 95-kilodalton fertilization antigen-2 from human sperm

Monoclonal antibodies (mAbs) were raised in mice against human sperm. Of the eight hybridomas secreting mAbs that react with human sperm, one, the Vic-1 antibody, was selected for detailed analysis because of its high degree of tissue specificity. The Vic-1 antibody was of the IgG1 subclass and demonstrated binding predominantly with the acrosomal regions of viable but not methanol-fixed noncapacitated and capacitated human sperm cells. It also reacted with the acrosomal and mid-piece regions of viable capacitated as well as noncapacitated murine sperm, but not with methanol-fixed murine sperm. The Vic-1 antibody was germ-cell specific as it did not react with any human somatic cell, tissue, or secretion examined including seminal plasma. The Vic-1 antibody significantly (p = 0.0006) inhibited human sperm penetration of zona-free hamster oocytes in a concentration-dependent manner; at 15 g% concentration it almost completely blocked sperm penetration. The antibody significantly reduced the acrosome reaction and the release of acrosin activity in human sperm cells. There was no effect of the Vic-1 antibody on percentage of motile sperm, although it significantly affected motility characteristics such as linearity, amplitude of lateral head displacement, and beat frequency; motility parameters involved in the hyperactivation phenomenon related to capacitation and the acrosome reaction. The Vic-1 antibody recognized a predominant antigen of 95 kDa, designated fertilization antigen-2 (FA-2), in Western blot and immunoprecipitation procedures using human sperm preparations. The FA-2 antigen was isolated from human sperm preparations by using an immunoaffinity column containing the Vic-1 antibody.