Coexistence of Hepatitis B Surface Antigen (HBsAg) and Heterologous Subtype-Specific Antibodies to HBsAg among Patients with Chronic Hepatitis B Virus Infection

Background. The coexistence of hepatitis B surface antigen (HBsAg) and antibodies to HBsAg (anti-HBs) in patients with chronic hepatitis B virus (HBV) infection has been explained by the presence of viral escape mutants. Yet, no systematic analysis of such patients has been performed. We analyzed both the HBV strains and the nature of anti-HBs in such patients. Methods. Four hundred eleven patients with chronic HBV infection were tested for the presence of anti-HBs. The sequences of the HBsAg coding region were analyzed. Anti-HBs were purified and examined in commercial assays alone and with 3 different HBsAg subtypes. Results. Twenty patients had positive results for anti-HBs. This serological status remained stable for 12 months (as tested thus far). Amino acid substitutions and/or variations on HBsAg were found in 13 patients, and the HBV isolates from 4 others were wild types. Importantly, no significant difference in the occurrence of amino acid substitutions within the HBsAg was found in HBV isolates from patients with and without anti-HBs. Purified immunoglobulin fractions from serum samples from patients were reactive to HBsAg but had a lower specific activity, compared with those taken from immunized persons. Anti-HBs in patients were directed to the HBsAg subtypes other than the coexisting one. No circulating immune complex could be detected in these patients. Conclusion. HBsAg and anti-HBs with an unmatched specificity coexisted in 4.9% of patients. The presence of anti-HBs was not associated with the appearance of specific HBV mutants in patients with chronic infection. Apparently, the presence of anti-HBs in patients with chronic HBV infection did not lead to a selection of HBV escape mutants. Hepatitis B virus (HBV) causes acute, self-limiting, and chronic infections in humans [1]. The antibody response to hepatitis B surface antigen (HBsAg) appears during the late phase of infection. The antibodies to HBsAg (anti-HBs) are able to neutralize HBV infectivity and, therefore, clear circulating HBsAg and infectious HBV particles from peripheral blood. The presence of