In 1964 Franklin and Dukes reported that women who were sterile owing to unknown causes possessed a high incidence of sperm agglutinating antibodies (SA-Abs) in their sera (2,3). We, however, recognized the occurrence of spontaneous sperm agglutination in many cases on examining patients’ sera. To avoid false positive results due to nonspecific sperm agglutination, we instituted a sperm-immobilizing reaction to detect the antibodies, because this reaction required a complement and was more specific in showing the nature of the antibody. Since 1965 the sperm immobilization test (SI-test) has been applied to examine antisperm antibodies in sterile women, and the sperm immobilizing factor was found in 12% of women sterile owing to unknown causes (9). This factor was proved to require a complement to immobilize spermatozoa, and it was fractionated in IgG and IgM sediments, absorbed specifically with washed human spermatozoa, but not with other human tissues. Fifty percent activity of this factor was dissociated from the absorbed spermatozoa by heating at 60°C for 20 minutes or by glycine-HCl (pH 2.5) buffer. Therefore it was proved that this factor is likely to have antibody characteristics. When the patients’ sera were examined for antibody activities by using both SA-test and SI-test, the positive correlation of sterility to positive antibodies was much greater in SI-Abs than SA-Abs, as shown in Table 28.1.
