A polymorphic antigen displaying different molecular weights in sheep and cattle sera

The polymorphic antigen Bl is present, exhibiting different molecular weights, in both sheep and cattle sera. The molecular weight of the antigen, purified from both sera by a specific immunoabsorbent, was analysed by SDS polyacrylamide gel electrophoresis and calibrated gel filtration. Results indicate that only one subunit, 35 000 MW, forms cattle Bl while a further subunit, 60 000 MW, is present in sheep Bl. The antigen activity is localized on the 35 000 MW subunit, which appears to be the same in both species.