Antigenic Stimulation and Blocking of Pregnancy in Mice by an Anti-Idiotypic Antibody to Progesterone

PROBLEM: The present study was carried out to see if the anti-idiotypic (anti-Id) antibody (Ab2) to progesterone could mimic the immunogenicity of the steroid hormone by giving rise to antiprogesterone antibodies (Ab3) and whether these antiprogesterone antibodies (Ab3) were biologically active. METHOD: Twenty virgin female Balb/C mice were actively immunized with the anti-Id antibody (Ab2). The antiprogesterone antibody (Ab3) titres in the serum were determined and the animals were used for fertility studies. In the passive immunization studies Balb/C female mice were injected i.p. with 100 μg of anti-Id antibody to see its effect on pregnancy. RESULTS: The actively immunized animals when mated showed 80% reduction in their fertility rate. The duration of infertility (20–121 days) in these animals could be directly correlated with the concentration of antiprogesterone antibody (Ab3). The anti-Id antibody (Ab2) blocked pregnancy in 80% of the passively immunized mice. CONCLUSION: The studies show that anti-Id antibody to progesterone could mimic the immunogenicity of progesterone and give rise to antiprogesterone antibodies (Ab3). The anti-Id antibody successfully blocked pregnancy in mice both after active and passive immunization.