Non-specific effects of passive immunization on implantation in the rabbit

Passive immunization with goat anti-rabbit uteroglobin antiserum prevents implantation in the rabbit. The dose of antiserum was too low to neutralize all of the uteroglobin present on Day 5 of pregnancy, however, and the effect could not be shown to be specific, because 'control' treatments with goat antiserum to chick avidin or normal goat serum also prevented implantation. Non-specific antisera raised in rabbits had little or no effect on implantation. Partial purification of antibodies from the non-specific goat antisera reversed their effect, while anti-uteroglobin gamma globulin still reduced implantation. Fluorescein-labelled gamma globulin fractions of anti-avidin and anti-uteroglobin both bound to blastocysts, but pure FITC-IgG showed binding only of anti-uteroglobin. Both anti-avidin and anti-uteroglobin IgG prevented implantation. It is concluded that the effect on implantation is not necessarily achieved via a specific antigen.