Sperm immobilizing and fertilization-blocking monoclonal antibody 2C6 to human seminal plasma antigen and characterization of the antigen epitope corresponding to the monoclonal antibody.

A monoclonal antibody (Mab 2C6) with strong sperm immobilizing and agglutinating activities was generated by cell fusion between spleen cells from a mouse immunized with human seminal plasma (HSP) and mouse myeloma cells. It also showed a strong inhibitory effect on human sperm-egg interaction. The corresponding antigen was present on the whole surface of ejaculated spermatozoa. In male genital organs, immunostaining with Mab 2C6 was observed in epididymis and seminal vesicle but not in testis. By Western blotting, immunostaining with Mab 2C6 was detected around the 15-25 kDa region under both reducing and non-reducing conditions. The antigen corresponding to Mab 2C6 was susceptible to treatment with periodate or trifluoromethanesulfonic acid. The antigenic activities were slightly increased by treatment with neuraminidase but reduced by further treatment with glycosidases. Enzymatic digestions with pronase and papain also reduced the antigenic activities. The antigen molecules exhibited a strong binding affinity to RCA lectin. These results indicated that Mab 2C6 recognized one of the components which might be secreted from epididymis or seminal vesicle and bind to ejaculated spermatozoa as a sperm coating antigen. The corresponding antigen seems to be a glycoprotein and its carbohydrate moiety has an important role in the conformation of the antigen epitope.