Characterisation of a sperm coating auto-antigen reacting with antisperm antibodies of infertile males using monoclonal antibodies

Objective In a previous study a number of sperm-specific antigens were identified which reacted with antisperm antibodies from both infertile and vasovasostomised males. To investigate the localisation and distribution of these antigens and their role in male fertility, monoclonal antibodies were raised against them; immunoblotting techniques were used to select only those antibodies which competed with human antisperm antibodies for these human auto-antigens.
Design One antibody, NW21, reacted with an 18 kDa auto-antigen present on epididymal sperm but absent from testicular sperm. Immunohistochemical studies showed that the antigen is produced in small basal cells between the columnar epithelium of the corpus epididymis, passes up into the tubule and then coats sperm passing along the epididymis. Sperm stored in the cauda epididymis and ductus deferens stain strongly for this sperm coating glycoprotein.
Conclusions The localisation of this antigen supports the suggestion that auto-immune infertility may represent a response to epididymal rather than testicular sperm. Monoclonal antibodies raised to unique and immunologically accessible sperm coating proteins, produced in the epididymis rather than in the testis, would seem to present an excellent theoretical solution to male contraception.