Sperm-Coating Antigens Secreted by the Epididymi’s and Seminal Vesicle of the Rat

The sperm-coating antigens of the rat were studied with immunological techniques. A sperm-free epididymal fluid produced in immature rats stimulated with testosterone contained at least four antigens not present in blood serum. One or more of these antigens were found in all segments of the epididymis, vas deferens, and seminal vesicle. These antigens coated epididymal sperm and were not completely removed in utero. The absence of sperm in the fluid and the lack of any immunological reaction with testicular tissue or sperm indicate that these antigens are indeed secreted by the epididymis to associate with sperm and are not simply of testicular or sperm origin. A protein of M r 50,000 (which was not one of the epididymal antigens) was isolated from the saline-soluble fraction of seminal vesicle secretions and found to bind tightly to epididymal spermatozoa but not to rat red blood cells. The protein was not removed from the sperm surface by washing but was removed from ejaculated sperm following 4-5 h incubation in utero. The protein was revealed by immunohistochemical techniques in the epithelium of the seminal vesicle but not in the testes, any segment of the epididymis, or the vas deferens.