A monoclonal antibody against a hepatitis B e antigen epitope borne by six amino acids encoded by the precore region

Molecular basis for the high degree of antigenic cross-reactivity between hepatitis B virus capsids (HBcAg) and dimeric capsid-related protein (HBeAg): insights into the enigmatic nature of the e-antigen

The hepatitis B virus core gene codes for two closely related antigens: a 21-kDa protein that forms dimers that assemble as multimegadalton capsids, and a 17-kDa protein that also forms dimers but that do not assemble. The proteins, respectively referred to as core antigen (HBcAg) and e-antigen (HBeAg), share a sequence of 149 residues but have different amino- and carboxy-termini. Their structural and serological relationship has long been unclear. With insights gained from recent structural studies on immune complexes of the capsids, the relationship was reassessed using recombinant forms of the antigens and a panel of monoclonal antibodies (mAbs) commonly believed to discriminate between core and e-antigen. Surface plasmon resonance (SPR) was used to measure the affinities, in contrast to previous studies that used more error-prone and less sensitive plate-type assays. Four of the six mAbs did not discriminate between core and e-antigen, nor did they discriminate between e-antigen and dimers of dissociated core antigen capsids. One mAb (3120) was specific for assembled capsids and one (e6) was specific for unassembled dimers. Epitope valency of the e-antigen was also studied, using a sandwich SPR assay where e-antigen was captured with one mAb and probed with a second. The e-antigen is often considered to be a monomeric protein on the basis of monovalent reactivity with antibody pairs specific for either an alpha or beta epitope (in a prior nomenclature for e-antigen specificity). This model, however, is incorrect, because recombinant e-antigen is a stable dimer and its apparent monovalency is due to steric blockage. This was proven by the formation of a 2:1 Fab e6-e-antigen complex. These results suggest new approaches for the isolation of the authentic e-antigen, its biological assay, and its stabilization as an immune complex for structural studies.

Possible association of vigorous hepatitis B virus replication with the development of fulminant hepatitis

A 49 year-old man was referred to our hospital for fear of developing fulminant hepatic failure. There had been an outbreak of fulminant hepatitis B in a dialysis clinic in the western part of Honshu, Japan, that resulted in four deaths among six patients. After the sixth patient contracted severe hepatitis, all patients in the unit were screened biweekly for hepatitis B surface antigen (HBsAg) to detect newly infected patients as soon as possible. Our patient was the seventh victim, and on the day he gave a positive result for HBsAg, his hepatitis B virus (HBV) DNA level had reached 1.1 x 10(11) copies/ml as assessed by real time polymerase chain reaction. Sequence analysis of the causal HBV revealed the presence of a mutation in the precore region (nt 1896), two mutations in the core promoter (nt 1762 and nt 1764), and some minor mutations in the P gene that were restricted to the upstream region. These mutations are indicative of a virus with a high replicative rate that cannot secrete HBeAg. Taken together, these findings indicate that it is very likely that the replicative ability of the causal virus was as vigorous as that of HBV in hepatitis B e antigen-positive asymptomatic carriers with markedly high viral titers. The present case report provides clinical evidence of a possible association between the rapid spread of highly replicative HBV before host immunological recognition and the development of fulminant hepatitis.

An enzyme-linked immunosorbent assay with monoclonal antibodies for the determination of phosphorylated hepatitis B core protein (p21c) in serum

An enzyme-linked immunosorbent assay (ELISA) was developed for the determination of hepatitis B virus (HBV) core protein (p21c) using monoclonal antibody (mAb) directed to a phosphorylated C-terminal amino acid sequence that is not present in hepatitis B e antigen (HBeAg). HBV virions in the test serum were precipitated with horse polyclonal antibody to hepatitis B surface antigen (HBsAg), dissolved with Tween 20 and NaOH, and then neutralized. HBV core protein (p21c), released from HBV cores by this procedure, was sandwiched between immobilized mAb C33 directed to amino acids (aa) 133-140 of the core protein, fixed on a solid support and labeled mAb T2212 that recognizes aa 165-175, only when they are phosphorylated. The method was applied for the detection of phosphorylated p21c in sera from symptom-free carriers and patients with chronic hepatitis. The results indicated a higher extent of phosphorylation in p21c of HBV cores from symptom-free carriers than hepatitis patients.