Immunological approach to the characterization of the outer acrosomal membrane of boar spermatozoa

Antiserum to purified boar spermatozoan outer acrosomal membrane (OAM) was raised in rabbits and adsorbed with boar liver and serum glutaraldehyde cross‐linked immunoadsorbents. The IgG fraction of the antiserum was purified by (NH 4 ) 2 SO 4 precipitation followed by ion‐exchange chromatography. Indirect immunofluorescence showed bright fluorescent staining of the acrosomal cap of boar spermatozoa and to a lesser extent of the acrosomes of bull and goat spermatozoa after incubation with anti‐OAM‐IgG. Immuno‐electron microscopy further confirmed the specificity of the antibody for the OAM. Preincubation of the anti‐OAM‐IgG with isolated OAM, completely abolished its reactivity. When tested by ELISA, anti‐OAM‐IgG reacted with boar, bull, goat, and human spermatozoa; however, its binding activity to boar spermatozoa was significantly greater as compared to spermatozoa from the other species tested. In an effort to identify OAM antigens recognized by this antiserum, the isolated boar OAM was labeled either with 3 H or with 125 I and solubilized by mild detergent treatment. The extracted components were immunoprecipitated with anti‐OAM‐IgG and protein A‐bearing S. aureus and the thus isolated antigens were analysed on SDS‐PAGE. The results suggest that anti‐OAM‐IgG recognized one high molecular 3 H‐labeled glycoprotein (270 kd), and four 125 I‐labeled polypeptides of lower molecular weight of the boar OAM.