The hybrid EIA test: a specific and sensitive assay for the detection of woodchuck antibody to hepatitis surface antigen (anti-WHs)

Characteristics of woodchuck hepatitis X-antigen in the livers and sera from infected animals

This study tests the hypothesis that woodchuck hepatitis virus encoded X-antigen expression correlates with viral replication, with hepatitis, or with both. Paired liver and serum samples from each of 55 infected woodchucks were used. Seven of 8 carriers with high levels of viral DNA in serum also had X-antigen in serum. In contrast, the frequency of X-antigen in serum was low among infected woodchucks that did not have viral surface antigen in the serum. Statistical analysis showed a significant relationship between X-antigen in serum and markers of viral replication. Woodchuck hepatitis X-antigen (WHxAg) expression in liver but not serum of carriers closely correlated with the presence of hepatitis. The finding of X-antigen in the liver of infected animals with hepatitis that cleared the virus surface antigen from serum also suggests that X-antigen is associated with ongoing hepatitis. Hence, the persistence of WHxAg in serum may signal continuing viral replication and, in liver, may contribute to the pathogenesis of chronic infection.

X antigen/antibody markers in hepadnavirus infections. Antibodies to the X gene product(s)

Antibodies to the X antigen of hepatitis B virus and woodchuck hepatitis virus were assayed in serial sera from infected individuals and compared with other markers of infection. Antibody to the X antigen was found in 11 of 17 (65%) patients and 17 of 40 (42%) woodchucks that were surface-antigen positive. In comparison, this antibody was found in 5 of 14 (36%) patients and in none of 4 woodchucks that were surface-antigen negative. In 5 of 6 patients showing seroconversion from hepatitis B e antigen to antibody, antibody to X appeared at or near the time of seroconversion. In patients persistently positive for e antigen, X antibody often appeared when viral DNA became undetectable in the serum. In 14 of 17 (82%) woodchucks positive for antibody to X antigen, it also appeared near or after the time that viral DNA in serum disappeared. X antibodies were detected with great frequency only in populations with high frequencies of other hepatitis B virus markers. The results are consistent with the conclusion that antibody to X antigen is a marker of hepadnavirus infections that seems to be associated with a decrease in viral replication. Antibodies to the X antigen, then, may be a host response to the replication complex of the virus.

X antigen/antibody markers in hepadnavirus infections. Presence and significance of hepadnavirus X gene product(s) in serum

The finding that X antigen is associated with hepatitis B core antigen particles and that serum hepatitis B e antigen derives from the cleavage of one or more core associated polypeptides raises the question as to whether core associated X antigen could be similarly generated and released into serum. To test this hypothesis, antisera raised to X antigen peptides were used to construct an enzyme-linked solid-phase immunoassay to detect X antigen in sera from patients infected with hepatitis B virus and from woodchucks infected with woodchuck hepatitis virus. X antigen was present in more than half of the individuals tested. There was a significant association between X antigen and markers of viral replication. Most individuals destined to become surface-antigen carriers had X antigen appearing before surface antigen, as did a smaller proportion of individuals transiently positive for surface antigen. A high frequency of X antigen was observed only in sera from human populations with a high frequency of other hepatitis B virus markers. These results suggest that X is a newly identified serum marker of viral replication that often appears before surface antigen in productive infections.

Vertical transmission of woodchuck hepatitis virus

One newborn and 24 fetal woodchuck litters from a woodchuck hepatitis virus (WHV) endemic population were examined for serological or hepatic evidence of WHV. In 18 of 24 fetal litters, there was detectable WHV DNA in the livers, either at explant culture or tissue extract. Most of those WHV DNA-positive liver extracts, which were examined by Southern blot, showed integration of WHV. However, WHV DNA replicative forms without integration were demonstrated in livers of two litters from late gestation. Woodchuck hepatitis surface antigen was detected in the sera of two other fetal litters from the late gestation period. WHV DNA was demonstrated in sera of three litters at different stages of ontogeny.