Radioimmunoassay for detecting hepatitis B core antigen in serum from patients with chronic hepatitis B infection.

Quiroga JA, González O, Carreño V, Mora I, Porres JC, Gútiez J, Hernández-Guío C.

The core antigen component of hepatitis B virus (HBV), HBcAg, may be used as a marker of viral replication. We describe a radioimmunoassay for HBcAg in serum, and compare results with those by other similar methods. Samples are centrifuged over a sucrose gradient containing 2-mercaptoethanol, and the resulting pellets are resuspended in a nonionic detergent solution. After a bead coated with anti-HBcAg is incubated with this suspension, 125I-labeled anti-HBcAg is added, and is also bound by the antigen. The specificity of the method was verified by blocking with purified IgG antibodies to HBcAg. When we tested by this method for HBcAg in sera from 60 patients with chronic HBV infection, all those with circulating HBV-DNA polymerase tested positive for HBcAg. All sera from HBV-negative controls showed no detectable HBcAg. The correlation between the presence of HBcAg and HBV-DNA polymerase was significant (r = 0.715, p less than 0.001). Samples can be tested more quickly and easily with this method, and its sensitivity compares well with that of other similar methods.