Complement-mediated effects of sperm head-directed human antibodies on the ability of human spermatozoa to penetrate zona-free hamster eggs

The ability of immunoglobulins of IgA, IgG, and IgM classes to mediate complement-dependent membrane damage varies. Sera containing antisperm antibodies of differing immunoglobulin classes were studied, in association with complement, for their ability to alter human sperm penetration of zona-free hamster eggs. Sera that contained immunoglobulins of IgG, IgA, or IgM classes directed primarily against the sperm head (as determined by immunobead binding) were selected from men and women judged to be at risk for immune causes of infertility. Spermatozoa were incubated in these sera in the presence and absence of complement. Following an additional incubation in a modified Biggers, Whitten and Whittingham medium, zona-free hamster eggs were inseminated with these spermatozoa. Antibodies known to fix complement (IgG and IgM) diminished the percentage of eggs penetrated and the number of penetrating sperm per egg without impairing the ability of sperm to contact the egg surface, as judged by comparable numbers of spermatozoa adherent to the oolemma. IgA, which cannot fix the first component of complement, did not alter the ability of sperm to penetrate eggs.