PROGESTERONE-INDUCED ACROSOME REACTION - POTENTIAL ROLE FOR SPERM ACROSOME ANTIGEN-1 IN FERTILIZATION

We have established a monoclonal antibody (mAb) AG7 defining a sperm a crosome antigen-1 (SAA-1) on spermatozoa from the human and several ma mmalian species. MAb AG7 inhibits fertilization of mouse eggs in vitro and in vivo. An important characteristic of mAb AG7 is its inhibition of the rise in intracellular calcium induced by progesterone in human spermatozoa. Here we show that, following the acrosome reaction, SAA- 1 is lost from the cap of human spermatozoa but remains detectable in the equatorial region. Acrosome reaction assays demonstrated a clear d ifference between progesterone- and A23187-induced acrosome reactions. For induction of the acrosome reaction with progesterone, a minimum c apacitation time of 6 h was required. A23187 induced the acrosome reac tion regardless of capacitation time. MAb AG7 completely inhibited the progesterone-induced acrosome reaction, but not the A23187-induced ac rosome reaction in human spermatozoa. Differences in the pattern of ca lcium flux induced by the two agents might account for this phenomenon . The inhibition of the progesterone-induced acrosome reaction by mAb AG7 implies a regulatory function of SAA-1 during the human sperm acro some reaction.