(A) A SDS-PAGE showing the purified recombinant preS. (B) Binding of HBsAg to anti-HBs and to polyclonal anti-preS. An ELISA Kit for HBsAg detection was used to detect HBsAg in the serum sample of an HBeAg positive patient (black square). Recombinant S protein (white square) was used as control. Binding of HBsAg to polyclonal anti-preS (white circle) was detected by adding recombinant S protein to a 96-well microplate which was coated with the polyclonal anti-preS antibody, using the same HRP-anti-HBs in the HBsAg kit. The binding to polyclonal anti-preS by antigens in an HBeAg positive patient serum sample is shown as (black circle). The X axis is plotted in logarithm. The absorbance at 450 nm has been subtracted by the background.