PROBLEM: Autoantibodies to zona pellucida (ZP) have been implicated as a cause of infertility in woman by three lines of clinical and laboratory evidence.
METHOD: First, positive anti-zona activities, as assessed by the passive hemagglutination reaction (PHAR) using bovine red blood cells sensitized with porcine zona antigen, were detected in 45 of 1,872 serum samples collected from infertile women, but in only three (two nonpregnant and one pregnant) of 592 serum samples from control subjects. Their incidence in 320 women with unexplained infertility (5.6%) was much higher than that in 1,552 women with infertility of known cause (1.7%, P < 0.01), which was comparable to the incidence observed in 193 age-matched fertile nonpregnant and pregnant women (1.5%, P < 0.05). None of the serum samples from 292 age-matched adult men and 100 children of between 5 and 10 years old gave a positive PHAR. Second, follow-up study for a minimum of 2 years with treatment revealed that no pregnancy occurred in 11 infertile women with a consistently positive PHAR, and only three pregnancies in 19 infertile women with a fluctuating positive PHAR. Third, three of seven serum samples from women who gave a consistently positive PHAR produced strong immunofluorescence reactions on human ZP even after adsorption with porcine and human AB blood cells. Pre-exposure of human ZP to the sera showing positive immunofluorescence, including that of one patient undergoing an in vitro fertilization program, greatly diminished the number of spermatozoa of normal quality that bound to and penetrated across human ZP.
CONCLUSIONS: The observed high incidence of anti-zona activities and long-term resistancy to treatment in women with unexplained infertility may be closely correlated with inhibition of sperm-egg interaction by anti-zona autoantibodies produced in these women.