Assessment of acrosome-reacted boar spermatozoa using monoclonal antibody GB 24 and propidium iodide

Fluorescein-labeled GB 24, a mouse monoclonal antibody, was evaluated as an acrosomal dye for boar spermatozoa that had previously been stained with propidium iodide (PI) to assess sperm viability. A specific sperm-staining pattern with fluorescein-labeled GB 24 was shown to be associated with acrosome reaction on freshly ejaculated sperm when fixed with acetone or induced with ionophore A 23187, whereas the presence of PI staining was typical of dying spermatozoa. The GB 24-PI procedure was as accurate as the glutaraldehyde method in assessing acrosomal presence or absence on freshly ejaculated spermatozoa when spontaneous or A 23187-induced acrosomal reactions were considered. Approximately half of A 23187-induced spermatozoa with acrosomal loss did not exhibit a PI fluorescence; these were potentially viable acrosome-reacted spermatozoa. On semen diluted in a boar sperm-specific diluent (BTS-A) and stored, percentages of spermatozoa with nonintact acrosome from glutaraldehyde and GB 24-PI were not significantly different. Conversely, data from GB 24-PI was significantly lower than those from glutaraldehyde when semen were undiluted. This suggested that spermatozoa with reacted acrosome gradually lost their ability to bind with GB 24. Providing unequivocal and rapid scoring of acrosome-reacted spermatozoa, the GB 24-PI procedure may be a valuable tool in the evaluation of the acrosomal status of porcine fresh spermatozoa.