Determination of immunoglobulin classes and subclasses of sperm immobilizing antibodies in infertile women and the inhibitory effect of IgG4 subclass on the sperm immobilizing antibody activity

Immunoglobulin classes and subclasses of sperm immobilizing antibodies (SI-Abs) in the sera of sterile women were determined by the absorption of patients' sera with Staphylococcus aureus and immunoadsorbents bound with class or subclass-specific anti-human immunoglobulin antibodies. Among 18 patients' sera tested, 16 had the IgG-dominant SI-Abs and the remaining 2 sera contained IgM-dominant SI-Abs. From the former patients' sera, 9 were further studied to determine the IgG subclasses; 6 of them had IgG1-dominant SI-Abs, one IgG2-dominant, and in the other two IgG1 and IgG2 were equally dominant. Interestingly, SI-Ab activities in 6 of the 9 patients' sera increased after absorption of IgG4 subclass and the addition of IgG4 purified from an SI-positive patient to the same patient's serum diminished the SI-Ab activities.