Partial physico-chemical and immunological characterization of bovine semen isoantigens.

Antisera prepared by immunizing 10 virgin heifers with semen pooled from eight bulls of four dairy breeds reacted in immunodiffusion tests to indicate that bovine semen contains at least four isoantigens. No visible precipitin reaction was observed when such sera were diffused against vesicular gland fluid, but all four antigens were present in the testicular fluid, cauda epididymal plasma, cauda epididymal sperm and caput epididymal fluid, indicating that they arise from the testes. This viewpoint was supported by the results of immunofluorescence investigations. Bovine seminal plasma was fractionated into five protein components on a Sephadex G-200 column. One area of isoantigenicity was associated with the trailing portion of the first protein peak and another was found in the leading portion of the second peak. There was no clear association of any individual precipitin line with only one of these molecular weight regions; in fact, the observed recurrent multiplicity suggested a dependent relationship. These antigenic regions corresponded to molecular weight estimation points of 285,000 and 110,000 daltons, respectively. The isoantigens, designated 1 to 4 in order of proximity to the antiserum well, were increasingly more heat labile and Pronase vulnerable. Isoantigen 1 was destroyed by heating at 65 C for 30 min, antigens 2 and 3 at 65 C for 15 min, while antigen 4 was destroyed by 56 C