Acrosomal autoantigens of guinea pig sperm. I. The purification of an aspermatogenic protein, AP2.

A soluble aspermatogenic autoantigen (AP2) capable of inducing experimental allergic orchitis (EAO) in the guinea pig has been isolated from the soluble acrosomal contents (SAC) released from guinea pig cauda epididymal sperm during the in vitro Ca+2 ionophore A23187-induced acrosome reaction. AP2 purification was achieved by heat inactivation of SAC enzymatic activity, followed by chaotropic solubilization and ultracentrifugation, gel filtration on Sephadex G-50, preparative isoelectric focusing, and SDS-polyacrylamide gel electrophoresis. Approximately 80 micrograms of AP2 was obtained from 1 to 2 x 10(10) cauda epididymal sperm. AP2 has a m.w. of 9500 +/- 1500 as determined by unreduced SDS-PAGE and an isoelectric point of 5.52 +/- 0.11. Amino acid analysis of AP2 indicates that it is a protein. AP2 has no detectable hexose or hexosamine as determined by gas liquid chromatographic analysis and is therefore probably not a glycoprotein. Five micrograms of AP2 are capable of inducing severe EAO in 100% of guinea pigs tested, whereas 0.5 to 2.0 micrograms induces mild lesions consisting primarily of aspermatogenesis in 66% of guinea pigs tested.