CD4-mediated anchoring of the seminal antigen gp17 onto the spermatozoon surface.
A soluble 1, 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, we 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, put that only the 1 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 part of the treated spermatozoa exhibited CD4 immunostaining, which remained localised on the post-acrosomal region. The possible function of CD4 and gp17 on male germ cells is discussed.
Bergamo
P
P
Dipartimento di Fisiología Generale ed Ambientale, Università di Napoli, Italy.
Balestrieri
M
M
Cammarota
G
G
Guardiola
J
J
Abrescia
P
P
D000818:Animals; D001053:Apolipoproteins; D053399:Apolipoproteins D; D015704:CD4 Antigens / Q000276:immunology*; D002352:Carrier Proteins / Q000276:immunology*; D005591:Chemical Fractionation; D004542:Ejaculation; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D008297:Male; D026901:Membrane Transport Proteins; D051379:Mice; D012661:Semen / Q000276:immunology; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000276:immunology*
C024328:APOD protein, human; D001053:Apolipoproteins; D053399:Apolipoproteins D; D015704:CD4 Antigens; D002352:Carrier Proteins; D018985:Epitopes, B-Lymphocyte; D006023:Glycoproteins; D026901:Membrane Transport Proteins