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Role of guinea-pig sperm autoantigens in capacitation and the acrosome reaction

Summary. Three autoantigens, S, P and T, have been isolated from epididymal spermatozoa of guinea-pigs. S and P are soluble antigens present on the acrosomal membranes and acrosome matrix. T antigen, a family of several membrane glycoproteins, is distributed over the whole cytoplasmic membrane and on the external acrosomal membrane. Specific antibodies were used to localize the antigens on capacitated and acrosome-reacted spermatozoa and to define their role in acrosome reaction. After capacitation S antigen appeared on the head surface and there was an apparent clustering of T antigen. Both phenomena were prevented by the presence of specific antibodies in the capacitating medium. The acrosome reaction was inhibited both by anti-T and anti-S antibodies as well as by Fab fragments of the same antibodies. The localization of S, P and T antigens on the inner acrosomal membrane after the acrosome reaction suggests that they could also play a role in subsequent steps of fertilization.