MONOCLONAL-ANTIBODY TO HUMAN FERTILIZATION ANTIGEN-1 (FA-1) INHIBITS BOVINE FERTILIZATION IN-VITRO - APPLICATION IN IMMUNOCONTRACEPTION

A monoclonal antibody (mAb) to the human sperm plasma membrane protein , fertilization antigen-1 (FA-1), was tested for its reactivity with b ovine spermatozoa and its effects on bovine fertilization in vitro. We stern blot analysis revealed that the FA-1 mAb reacted with proteins o f similar molecular mass (53 +/- 2 kDa) in human and bovine sodium deo xycholate (DOC)-solubitized sperm extracts. Indirect immunofluorescenc e, using epifluorescence microscopy and laser scanning confocal micros copy, revealed that the FA-1 antigen is present in the post-acrosomal region of bovine spermatozoa, which is similar to human FA-1 localizat ion. In bovine in vitro fertilization (IVF) trials, using oocytes obta ined from slaughterhouse ovaries, addition of 20, 40, or 80 mu g/ml of FA-1 mAb to the IVF medium resulted in a linear decrease in the ferti lization rate from 86.3% in the controls to 54.6%, 21.6%, and 1.8% in the respective experimental groups (P < 0.01). There was no inhibitory effect (P > 0.10) of the FA-1 mAb on percent sperm motility or other motility characteristics tested, suggesting that human FA-1 mAb inhibi ts bovine sperm cell function at some point after capacitation. In con clusion, the evolutionarily conserved antigen FA-1 has a molecular ide ntity in bovine sperm similar to that in human sperm, and mAb to human sperm FA-1 inhibits fertilization of bovine oocytes. These results in dicate that FA-1 is a promising candidate for the development of a con traceptive vaccine. The research also suggests that bovine species cou ld be used as a model for investigating the use of FA-1 as an immunova ccine in ruminants.