Effects of sperm-reactive antibodies present in human infertile sera on fertility of female rabbits.

Sera (n = 19) from immunoinfertile patients were analyzed for cross-reaction with lithium diiodosalicylate (LIS)-solubilized human sperm extract (HSE), protamine and fertilization antigen (FA-1) using an enzyme-linked immunosorbent assay (ELISA). Among the sera tested, 63% reacted with HSE, 58% with protamine and 63% with FA-1. None of the sera from male or female infertile patients was found to contain immune complexes, indicating the antibodies were present in free form. The seven sera that reacted strongest with HSE inhibited human sperm function in sperm penetration of zona-free hamster ova and were associated with fertilization failure in human in vitro fertilization (IVF) technique. The six of these sera that showed binding to rabbit sperm, especially in the head region, also inhibited fertility in female rabbits. Antibodies reactive with FA-1 and not those reactive with protamine reduced fertility in female rabbits. These results indicate that mammalian sperm have several fertilization-related antigens that are evolutionarily conserved. These data also indicate that the rabbit can provide an animal model for studying antibody-mediated human infertility.