CD4-mediated anchoring of the seminal antigen gp17 onto the spermatozoon surface

A soluble 17 kDa glycoprotein, namely gp17, was previously isolated from human semen and used to obtain mouse monoclonal or chicken polyclonal antibodies. This protein was shown to bind CD4(+) T-cells and to soluble recombinant CD4 in vitro. Here, pie report that the anti-gp17 monoclonal antibodies are captured by ejaculated spermatozoa and that gp17-like antigens are released by cell acid extraction. Immunoblotting experiments with monoclonal antibodies indicated that SDS-lysates from spermatozoa contain proteins with the same electrophoretic and antigenic properties of CD4 and gp17. Anti-CD4 mouse monoclonal antibodies were used to coprecipitate from NP40-lysate proteins reacting with chicken anti-gp17 antibodies. Analytical chromatography demonstrated that-a number of gp17-like forms are present in the seminal plasma, but that only the 17 kDa species can be detected in the spermatozoa lysate. This protein was localised by immunofluorescence on the post-acrosomal region of the spermatozoon. The same surface domain was also reactive with anti-CD4 antibodies. After treatment to induce in vitro capacitation, gp17 was detected all over the spermatozoon head. Conversely, only a minor pare of the treated spermatozoa exhibited CD4 immunostaining, which remained localised on the postacrosomal region. The possible function of CD4 and gp 17 on male germ cells is discussed. (C) American Society for Histocompatibility and Immunogenetics, 1997. Published by Elsevier Science Inc.