Small and large forms of hepatitis B e antigen in the serum: determination by two-site sandwich radioimmunoassay with monoclonal antibodies.

Serum samples containing hepatitis B e antigen (HBeAg) were subjected to electrophoresis in agarose, and fast-migrating 'small' HBeAg and slow-migrating 'large' IgG-associated HBeAg were pooled separately. HBeAg of each category was determined by a two-site radioimmunoassay that sandwiched HBeAg between monoclonal antibody (anti-HBe) against one epitope of HBeAg, fixed on a solid support, and anti-HBe against another epitope, labelled with radioiodine. Eighteen sera in which small HBeAg dominated revealed activities of hepatitis B surface antigen-associated DNA polymerase significantly higher than 14 sera in which large HBeAg dominated (logarithm of ct/min, mean +/- s.e. 3.36 +/- 0.08 versus 2.14 +/- 0.11, P less than 0.01). Shift from small HBeAg to large HBeAg was observed, along with the disappearance of DNA polymerase, in the serum from two carriers who seroconverted to anti-HBe.