Immunology: Identification of human sperm surface glycoproteins by sperm membrane-specific autoantibodies

In order to identify the surface antigens of human spermatozoa recognized by the sera of immune infertile men, sperm membrane-specific antibodies were obtained from three serum samples exhibiting high titres of antibodies with different sperm-binding patterns. Serum antibodies were adsorbed onto normal motile spermatozoa and subsequently eluted from the sperm membrane. Using the immunoblotting technique under renaturating conditions, the sperm-eluted antibodies were tested against an electrophoretically fractionated sperm membrane preparation. A total of 15 protein bands ranging from 110 to 16 kDa were defined, but the immunoblot profiles differed quantitatively and qualitatively from one serum to another. Only two polypeptides were recognized by the three sperm membrane-specific antibody preparations; one of 90 kDa and another of 110 kDa. Blots were also used for the affinodetection of specific oligosaccharide side chains. Three lectins were tested (concanavalin A. Pisum sativum, and wheat germ agglutinin). Of the 15 protein zones recognized by the antibodies, 11 bound at least one lectin and should contain glycopeptides with oligosaccharides of four different types: N-linked biantennary complex type, N-linked fucosylated complex type, N-linked lactosaminyl complex type with terminal sialic acid and polysialyl type oligosaccharides. Further analysis of these glycoproteins will be pursued with sperm-associated antibodies eluted from the ejaculates of infertile men in order to define those with a potential role in the fertilization process