Antibody to pre-S antigens in hepatitis B virus infection

Properties of a recombinant yeast-derived hepatitis B surface antigen containing S, preS2 and preS1 antigenic domains

Yeast cells have been engineered to express mixed HBsAg particles containing the S and a modified large (L*) protein. Their construction resulted in reduced protease sensitivity, reduced glycosylation and complete inactivation of the polymerized human albumin binding site. The particles exposed the S, preS1 and preS2 antigenic determinants and induced an immune response against the three domains. Highly purified preparations have been obtained and are presently being tested in human volunteers.

Fine specificity of human antibody response to the PreS1 domain of hepatitis B virus

The preS1 domain of hepatitis B virus envelope proteins contains a site of attachment to the hepatocyte membrane that has been shown to evoke virus-neutralizing antibodies. Using synthetic peptides, we have examined kinetics and specificity of the anti-body response to preS1 during acute and chronic HBV infection. Antibodies against two continuous B cell epitopes, p (21-32) and p (32-47), which overlap with the virus receptor for hepatocytes, were detected in 17 (28%) and 28 (47%) patients, respectively, of 60 patients who were tested during acute hepatitis B. Serial testing demonstrated these anti-preS1 specificities in more than 50% of patients who became virus free. By contrast, five patients with chronic evolution of hepatitis B and 61 of 66 patients with an established chronic HBV infection were negative, independent of serological profile and liver disease activity. Fifteen (22.7%) patients with chronic hepatitis B were positive for antibody to the C-terminus p (94-117) preS1 sequence that, unlike the acute-phase anti-(21-32) and anti-(32-47) reactivities, did not behave as a virus-precipitating antibody. Acute-phase sera were found to also contain virus-precipitating antibodies directed against conformational preS1 epitopes. These results indicate that the preS1 site, which contains the binding activity for the hepatocyte membrane, elicits an early antibody response during acute hepatitis B. A defect in such antibody repertoire may participate in the chronicity process as a result of continuing reinfection of hepatocytes by circulating virions.

Antibody response to pre-S2 and hepatitis B virus induced liver damage

Antibodies to the pre-S2 encoded sequence of the hepatitis B virus (HBV) envelope were detected in 83% of patients recovering from acute hepatitis B. Such antibodies were absent in cases showing chronic evolution and were found in less than 10% of chronic hepatitis B cases, with no relation to liver disease activity. In acute infection anti-pre-S2 became detectable when maximum liver damage had already occurred and was still detectable in 30% of the cases tested 5-7 years after recovery, as well as in 40% of healthy individuals with naturally acquired immunity to HBV. 10 out of 20 recipients of a plasma-derived, pre-S2-containing, HB vaccine acquired anti-pre-S2 and had no evidence of concurrent liver damage or of autoimmune reactions to human albumin or of suppression of the anti-HBs response. These findings indicate that the antibody response to pre-S2 is a marker of HBV clearance and has no role in the pathogenesis of HBV-related liver damage.

Methods for the study of pre-S proteins of hepatitis B virus and their antibodies: pathogenetic and clinical implications

The envelope gene of hepatitis B virus (HBV) consists of a large open reading frame which codes 3 different polypeptides by the variable use of 3 contiguous regions: the pre-S1, pre-S2 and S regions. The protein coded by the entire sequence (L protein) is identified by its unique pre-S1 epitopes and has a role in virus assembly and secretion. Pre-S1 antigens are expressed preferentially on virions and are less abundant, but present, on subviral particles. The pre-S2 sequence contains a species-specific receptor for polyalbumin, which has been implicated in virus binding to hepatocytes. Methods have been recently developed to measure pre-S1 and pre-S2 levels in serum and available data indicate that these assays may be useful in prognostic assessment of acute hepatitis B and to measure virus replication in chronic infection, although further studies are certainly needed to define specificity and sensitivity compared to conventional HBV markers. Both pre-S1 and pre-S2 are highly immunogenic and elicit anti-pre-S antibodies. Methods for detection of anti-pre-S in human sera have proved difficult to be developed due to unspecific reaction of serum components with pre-S sequences and epitope variability of the immune response in humans. Anti-pre-S2 seems a marker of recovery from acute infection, while evidence of its involvement in liver damage is weak. Both anti-pre-S2 and anti-pre-S1, but we have limited information on the latter, may be involved in virus neutralization. These issues are particularly relevant for future HB vaccine development, as it is proposed that inclusion of strategic pre-S sequences could increase efficacy.