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, on e, the Vic-1 antibody, was selected for detailed analysis because of i ts high degree of tissue specificity. The Vic-1 antibody was of the Ig G, subclass and demonstrated binding predominantly with the acrosomal regions of viable but not methanol-fixed noncapacitated and capacitate d 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-I antibody si gnificantly (p = 0.0006) inhibited human sperm penetration of zona-fre e hamster oocytes in a concentration-dependent manner; at 15 g% concen tration it almost completely blocked sperm penetration. The antibody s ignificantly reduced the acrosome reaction and the release of acrosin activity in human sperm cells. There was no effect of the Vic-1 antibo dy on percentage of motile sperm, although it significantly affected m otility characteristics such as linearity, amplitude of lateral head d isplacement, and beat frequency; motility parameters involved in the h yperactivation phenomenon related to capacitation and the acrosome rea ction. The Vic-1 antibody recognized a predominant antigen of 95 kDa, designated fertilization antigen-2 (FA-2), in Western blot and immunop recipitation procedures using human sperm preparations. The FA-2 antig en was isolated from human sperm preparations by using an immunoaffini ty column containing the Vic-1 antibody. These findings suggest that t he FA-2 sperm antigen of 95 kDa, which is tissue-specific and involved in human sperm cell function, may be a potential candidate for the de velopment of a contraceptive vaccine.