Analysis of auto-antigens in the human sperm membrane by a F(ab')2 blocking system

F(ab')2 preparations from human sperm-agglutinating and -immobilizing sera react with the sperm-membrane antigens without exerting immobilizing activity. Therefore, human spermatozoa, treated with such F(ab')2 fragments--and consequently with certain antigens blocked by the fragments--could be used in immobilization experiments with sperm-immobilizing sera. If a serum revealed a significantly reduced immobilizing activity on such F(ab')2-covered spermatozoa, compared with the effect on spermatozoa treated with F(ab')2 fragments from normal human serum, this was taken as evidence that the F(ab')2 fragments and the serum antibodies were directed against the same antigen or closely associated antigenic determinants. By cross-testing a panel of sera against the corresponding F(ab')2 preparations two main patterns of reactivity were observed indicating that at least two different auto- and iso-antigens (antigenic determinants) can be involved in sperm immobilization. Rather unexpectedly the reactivities in the F(ab')2-blocking system were not related to the different modes of agglutination observed with the sera (head-to-head, tail-to-tail or mixed agglutination).