Sperm immobilizing antibodies react to the 3-O-sulfated galactose residue of seminolipid on human sperm.

It is well known that very few women who possess sperm immobilizing antibodies in their sera can conceive naturally even though there are no abnormalities in their reproductive organs on routine medical examination. A monoclonal antibody (MAb), designated 2H12, was produced by immunizing a BALB/c mouse with the human choriocarcinoma cell line JEG-3. MAb 2H12 showed strong sperm immobilizing activities and reacted to sulfatide and seminolipids. The sperm immobilizing activities of 2H12 were clearly absorbed with sulfatide or seminolipid whilst several other sperm immobilizing MAbs that were made by immunization with human sperm or seminal plasma could not be absorbed with the same sulfoglycolipids. The sperm immobilizing antibodies in the sera of infertile women with unknown cause were also clearly absorbed with sulfatide or seminolipid. MAb 2H12-conjugated immunobeads (MAb 2H12-IMBs) bound to motile sperm. This binding of 2H12-IMBs to sperm was competitively inhibited either by 2H12 or women's sera containing sperm immobilizing antibodies, but not by normal women's sera or several other sperm immobilizing MAbs to human sperm. These results suggest that the sperm immobilizing antibody in women's sera is directed against the 3-O-sulfogalactose residue of seminolipid on the sperm membrane.