The principle of the double antibody sandwich ELISA is represented in Figure 1. In this assay the B2G present in samples reacts with the anti-B2G antibodies which have been adsorbed to the surface of polystyrene microtitre wells. After the removal of unbound proteins by washing, anti-B2G antibodies conjugated with horseradish peroxidase (HRP) are added. These enzyme-labeled antibodies form complexes with the previously boundB2G.