Purification of a human spermatozoal antigen

The lack of a more detailed study of spermatozoal antigens lies partly in the difficulty of adequate purification procedures. In the present work a spermatozoal cell membrane antigen was isolated using lithium 3,5-diiodosalicylate as the solubilizing agent. Its apparent molecular weight is 40 500 by gel filtration chromatography and 35 000 by dodecyl sulphate-polyacrylamide gel electrophoresis. Labelling of the antigen with 125I and subsequent radio-immunoprecipitation enabled the evaluation of specific binding to IgG and IgM molecules in sperm-agglutinating and sperm-immobilizing antisera. Adsorption experiments with the purified antigen resulted in significant titer reductions of the same antisera in the microsperm-agglutination and microsperm-immobilization tests. This indicates the presence of an antigen molecule on the human spermatozoa that reacts with IgG and IgM antibodies and with both types of antisera.