Radioimmunometric assay for hepatitis B surface antigen on the surface of infected cells

It has been difficult to differentiate hepatitis B surface antigen (HBsAg) on the cell surface from intracellular or intramembranous HBsAg that is not exposed to the host immune response. We describe here a radioimmunometric assay for HBsAg on the cell surface using HBsAg producing hepatocellular carcinoma cell lines and fibroblasts transfected with cloned hepatitis B virus DNA as models. The assay is sensitive, specific, simple and takes approximately 1 1/2 h. The procedure may be modified to compare quantitatively cell surface with intracellular HBsAg and to demonstrate other cell associated hepatitis B virus antigens such as HBcAg and HBeAg.