Duality of hepatitis B e antigen in serum of persons infected with hepatitis B virus: evidence for the nonidentity of e antigen with immunoglobulins.

Hepatitis B e antigen (HBeAg) is detected in the serum of some persons infected with hepatitis B virus. Owing to a close correlation of HBeAg and hepatitis B virus in the serum, it has been used as a practical indicator of infectivity. Two entities of HBeAg activity physicochemically different from each other were demonstrated in the serum of persons infected with hepatitis B virus. One was associated with a molecule that precipitated in 1.33 M ammonium sulfate solution, was larger than IgG, and had an electrophoretic mobility in the beta- to gamma-globulin regions and an isoelectric point of approximately pH 5.7. In contrast, the other HBeAg activity was associated with a molecule that was soluble in 1.33 M ammonium sulfate solution, was smaller than IgG, and had an electrophoretic mobility in the alpha-globulin region and an isoelectric point at pH 4.8. In spite of their marked physicochemical differences, a line of antigenic identity was clearly observed for them when they were tested against antibody to HBeAg by a them when they were tested against antibody to HBeAg by a double immunodiffusion method. The HBeAg activity associated with the large molecule was completely removed by an affinity column of anti-IgG, whereas the activity of the small molecule was not. These results indicate that, in the serum, HBeAg exists as a molecule smaller than IgG and also in association with IgG.