Biotinylated anti-progesterone monoclonal antibodies specifically target the uterine epithelium and block implantation in the mouse

Post-coital administration of a mouse monoclonal antibody (mAb) against progesterone (DB3; IgG1) prevents pregnancy in several species. Our previous studies in mice have shown that passively transferred DB3 specifically targets the uterus before the expected time of implantation, probably through progesterone-binding sites. DB3 and two other anti-progesterone mAbs, i.e. 1134 (IgG1) and 1164 (IgM), were biotinylated and 9 nmol of each (a dose known to reduce pregnancy rate by greater than 80% with unconjugated mAbs) was injected into BALB/c female mice 32 h post coitum (p.c). The biotin-mAb complexes were highly effective in blocking pregnancy (83–100%) compared with control animals that had received the biotinylated MOPC21 myeloma protein P3 (IgG1). Using the streptavidin-FITC (fluorescein isothiocyanate) reporter complex or second-stage anti-biotin-FITC antibodies, biotinylated conjugates of DB3, 1134 and 1164 were specifically localized on the uterine luminal epithelium at 68 h p.c. (i.e. 36 h after i.p. injection). Neither P3-biotin-treated pregnant mice nor biotinylated anti-progesterone mAb-treated pseudopregnant females showed a positive reaction. In addition, the localization of biotin-conjugated anti-progesterone mAbs could be blocked by absorption of the antibodies with free progesterone or progesterone conjugates prior to injection. These results show that localization to the uterine epithelium occurs with different anti-progesterone mAbs, and that this phenomenon is probably associated with progesterone-binding sites on the luminal epithelium.