Comparison of hepatitis B core antigens derived from human liver or synthesized in Escherichia coli and evaluation of their use in diagnostic assays for anti-HBc IgM

Hepatitis B core antigen (HBcAg) synthesized in Escherichia coli (clone PR 1-11) was compared with HBcAg purified from a liver obtained at autopsy of a patient with chronic active hepatitis B. The molecular weight determined by SDS-PAGE with subsequent transfer of the proteins to nitrocellulose paper, incubation with ¹²⁵I anti-HBc and exposure to X-ray film, was about 21,000 for HBcAg synthesized in E. coli and was slightly lower for the liver-derived HBcAg. In CsCI density gradients the liver-derived HBcAg had one peak at 1.32 g/ml, and the HBcAg synthesized in E. coli had two peaks at 1.34 and 1.30 g/ml. In a comparison of the immunological activity of both antigen preparations in an enzyme immunoassay, the liver-derived HBcAg was detected only up to a dilution of 1:320, whereas the HBcAg synthesized in E. coli was detected in dilutions up to 1:100,000. With both antigens, the same percentage of sera were positive for anti-HBc IgM from patients with acute (100%), convalescent (61%), past (5%) and chronic active (29-37%) hepatitis. These results indicate that tests for anti-HBc IgM performed with HBcAg synthesized in E. coli are at least as sensitive and specific as those using liver-derived HBcAg.