Nonimmunologic binding of horseradish peroxidase to hepatitis B surface antigen. A possible source of error in immunohistochemistry.

In the process of establishing the specificity of direct immunoperoxidase staining of liver tissue for hepatitis B surface antigen (HBsAg), an affinity of free horseradish peroxidase (HRP) for HBsAg in hepatocytes (ground-glass cells) was found. Of 95 patients, the horseradish peroxidase reaction was only positive in the livers of the 35 who were chronically HBsAg seropositive and not in the livers from 60 control patients with alcoholic cirrhosis who were HBsAg seronegative. Comparison studies using the orcein technic and immunoperoxidase methods confirmed the observation that both free horseradish peroxidase (not conjugated to an antibody) and HRP conjugated to an antibody unrelated to HBsAg had an affinity to the cytoplasm of hepatocytes containing HBsAg. The precise nature of this affinity is not known, but it is probably due to a reaction between an activated carbohydrate moiety of horseradish peroxidase and the free amino group of HBsAG.