TIME-COURSE OF SPONTANEOUS IN-VITRO SPERM ACROSOME REACTION

The acrosome reaction (AR) is an exocytotic process essential for sper m penetration of the zona pellucida and binding to the oocyte (DeJonge , 1994). Evaluation of in vitro AR can suggest fertility potential. Th e purpose of this study was to determine AR as a function of time afte r removal of sperm from the seminal fluid using a novel test, the Acro beads test (Fertility Technologies, Natick, Massachusetts), which uses paramagnetic beads coated with MH61, a monoclonal antibody that binds to acrosome-reacted sperm. Specimens were acquired from known fertile donors (n = 9) and in vitro fertilization (IVF) patients (n = 8) with no apparent male factor on the day of the IVF and processed by a mini percoll wash at 30 minutes after ejaculation. An aliquot of washed spe rm was then divided into two portions. The first was placed with the A crobeads (according to the manufacturer's instructions) and assessed f or bead binding after 6 and 24 hours with the beads. The second aliquo t of washed sperm was held at room temperature for 24 hours, then expo sed to the beads, with bead binding assessed at 6 and 24 hours later ( 30 and 48 hours after washing). The Acrobeads score was determined by assessing the binding of MH61 beads in each of four replicates with a resulting score of 1 (lowest) to 4 (highest). The mean (+/-SD) motilit y was 62.0% (7.5) at 6 hours, 52.3% (6.4) at 24 hours, 55.9% (10.4) at 30 hours, and 54.7% (8.4) at 48 hours after removal from the seminal fluid. At 6 hours after washing and exposure to the beads, the score w as 0.077 (0.27) with a range of 0-1; one donor specimen gave a score o f 1, while all others had a score of 0. At 24 hours postremoval from t he semen, donor and patient sperm were positive for the test, with a m ean score of 3.6 (0.65). The mean fertilization rate for the IVF patie nts was 64.4% (range 33-90). When sperm were held for 24 hours prior t o the test, there was little or no bead binding 6 hours later (score o f 0.46 +/- 0.77) and at 24 hours later (48 hours after washing) (mean score of 0.25 +/- 0.45). These data suggest that completion of the acr osome reaction occurs by 24 hours after removal of the sperm from the seminal fluid. Since the MH61 beads bind to specific residues on the i nner acrosomal membrane, these data also suggest that following the ac rosome reaction at 24 hours with removal of the outer acrosomal conten ts and acrosomal matrix, the inner acrosomal membrane may be modified in some way that does not allow MH61 beads to bind to the sperm.