The influence of anti-zona and anti-sperm antibodies on sperm--egg interactions

Anti-zona antibodies are effective inhibitors of fertilization in vitro and, regardless of whether passive or active immunization techniques are used, in vivo. Antibodies raised against unfractionated zona pellucida antigens are chiefly directed against a group of carbohydrate-rich components localized on the outer surface of the zona. The interaction of anti-zona antibodies with these sites induces the formation of a surface precipitate which occludes the sperm binding sites by a process of steric hindrance, and stabilizes the zona structure against digestion by the proteolytic enzymes of the sperm head. Active immunization studies indicate that the long-term induction of infertility without adverse side effects is feasible in both laboratory rodents and primates when the zona pellucida is used as a target. Anti-sperm antibodies also exhibit a capacity for inhibiting fertilization in vivo and in vitro. To determine the most appropriate detection method to screen patients for anti-sperm antibodies several homologous and heterologous antisera were analysed by 5 different agglutination and immobilization techniques and then compared for their ability to inhibit the fertilizing capacity of human spermatozoa using the zona-free hamster egg penetration test. The results obtained with the Franklin--Dukes tube--slide test exhibited the closest correlation with the anti-fertility activity of a given antiserum; this activity could be amplified by the addition of complement to the medium. It is concluded that antibodies directed against the sperm head are responsible for limiting the fertilizing capacity of human spermatozoa in vitro and that it is these antibodies of which attention should be focused to unravel the role that immunological factors play in the aetiology of infertility in vivo.