Detection of antibodies to pre-S2 encoded epitopes of hepatitis B virus by monoclonal antibody-enzyme immunoassay

Weak immunogenicity of the preS2 sequence and lack of circumventing effect on the unresponsiveness to the hepatitis B virus vaccine

The preS2 sequence is known to circumvent immunological unresponsiveness to the S protein and to induce a 'carrier' effect on the anti-S antibody production, in mice. In humans, an anti-S response was found in 100% and 97% of healthy subjects vaccinated with the S and S + preS2 preparations, respectively, whereas less than 50% of drinkers responded whatever the vaccine used. Anti-preS2 were found in 44% of healthy recipients of the S + preS2 vaccine, whereas there were no anti-preS2 responders in drinkers. Anti-preS2 remained undetectable in 32% of the blood donors hyperimmunized with the S + preS2 vaccine, whereas anti-S antibody boosted in all cases. In humans, in contrast to mice, immunogenicity of the preS2 sequence appears weak and the preS sequence does not circumvent the anti-S unresponsiveness.

Prognostic significance of pre-S2 antigen and antibody in fulminant hepatitis B. Evidence for heterogeneous serological responses

Serial sera were collected prospectively and from early on in the clinical course of ten patients with fulminant hepatitis B. These were analysed for HBV DNA (dot-blot technique), HBsAg, HBeAg, pre-S2-Ag and their respective antibodies. Two patterns emerged in nine of the patients. The first and well-recognised pattern of rapid clearance of antigens and appearance of antibodies was seen in four patients, all of whom survived. The second pattern seen in five patients was one of persistence of HBsAg and pre-S2 antigen and failure to detect antibodies but only one patient survived. The first pattern may reflect a more rapid cessation of virus replication and this may favour liver cell regeneration and recovery. In contrast, the second pattern may indicate continuing virus replication and liver cell damage which could contribute to the high mortality in some patients with fulminant hepatitis B.

Comparison of immunogenicity of recombinant and plasma derived hepatitis B antigen in guinea-pigs

Four different preparations of hepatitis B antigen (HBsAg) were tested in parallel with respect to their ability to elicit anti-HBs in guinea-pigs. We compared the effect of low doses (5 micrograms single dose and 30 micrograms total amount) of human plasma derived and recombinant HBsAg, in purified forms or prepared as vaccines, respectively. The highest titre of anti-HBs developed was detected in guinea-pigs immunized with plasma derived HBsAg, followed the by response in animals immunized with plasma derived vaccine. Purified recombinant antigen and recombinant vaccine exhibited poor immunogenicity compared with plasma derived antigen preparations. The increase in the dose of recombinant antigen (150 micrograms total amount) resulted in markedly improved response in two out of ten animals. Anti-HBs immunoglobulin fractions from pooled sera within each group of animals were isolated, partially purified, coupled to polystyrene beads and subsequently used in immunoradiometric assay with monoclonal 125I-anti-HBs. Only the anti-HBs isolated from pooled sera of animals immunized with purified plasma derived antigen met the requirements for high sensitivity and antigen specificity in such assay. Comparable properties were exhibited by the anti-HBs obtained from one guinea-pig immunized with a larger amount of recombinant antigen. With these two anti-HBs immunoglobulin preparations, amounts as low as 1 ng of HBsAg could be detected.

A biphasic pattern of anti-pre-S responses in acute hepatitis B virus infection

The clinical relevance of the immune response to the translation products of the pre-S1 and pre-S2 regions of hepatitis B virus was examined by testing sequential serum samples from 17 patients with acute self-limited hepatitis B and from two patients in whom chronic liver disease developed. Anti-pre-S antibodies were determined by enzyme immunoassays based on the inhibition of binding of monoclonal antibodies to epitopes in the pre-S1 and pre-S2 sequence. In acute, self-limited infection, anti-pre-S antibodies appeared in a biphasic pattern. The early antibodies were detected at the time of clinical signs of acute disease when HBsAg and often HBeAg were present, but hepatitis B virus DNA was no longer detectable in serum. Anti-pre-S levels then fell, but subsequently reappeared as the late antibody during the recovery phase, after development of anti-HBe, but before anti-HBs. Anti-pre-S responses were detected in 15 of 17 patients who recovered (88.2%) and in both patients with acute hepatitis B virus infection evolving to chronic liver disease. Although the early antibodies to pre-S1 and pre-S2 proteins appeared at the time of decreasing levels of infectious virus in serum in cases of self-limited infection, these antibodies also were transiently or continuously present with high levels of serum hepatitis B virus DNA in patients in whom chronic hepatitis B infection developed. Thus the anti-pre-S response in acute hepatitis is not a prognostic marker for clinical resolution.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Anti-PreS2 antibody assay for evaluating immune responses among recipients of recombinant hepatitis B PreS2 + S vaccine

A competitive radioimmunoassay was developed for measuring hepatitis B virus (HBV) anti-PreS2 antibody. The assay has been demonstrated to be highly specific for anti-PreS2 antibody and not subject to interference by other antibodies to HBV-specific antigens. This assay was used to evaluate anti-PreS2 antibody responses in a hepatitis B PreS2 + S vaccine human clinical trial in healthy adults.

Anti-pre-S(2) analysis after hepatitis B vaccination in haemodialysis patients

We investigated the development of anti-pre-S(2) antibodies by enzyme immunoassay and by Western blot analysis in a vaccination study in haemodialysis patients; both the Pasteur plasma vaccine retaining the pre-S(2) epitopes and the Merck, Sharp and Dohme (MSD) plasma vaccine containing only HBsAg were used. By enzyme immunoassay (EIA), one anti-pre-S(2) response at month 7 was registered in 23 patients after 5 injections with the 5 micrograms dose of Pasteur vaccine (PS group), whereas 6 responses were seen in 20 patients after 4 injections with the 10 micrograms dose (PD group). None of the 22 vaccines injected with MSD vaccine (40 micrograms) (4 injections, MD group) showed an anti-pre-S(2) response at month 7. In the Western blot an anti-pre-S(2) response was seen in 12 PS patients, in 8 PD patients and in none of the MD patients. Anti-pre-S(2) responses were predominantly observed in patients with a high anti-HBs response but exceptions occurred. Prevaccination anti-pre-S(2) positivity, in the absence of anti-HBc and anti-HBs, was detected in dialysis patients with EIA as well as Western blot, in 10.8 and 21.6%, respectively; similar findings were made in health care personnel. The possible nature of this phenomenon is discussed. In this study the Western blot technique has been shown to be a suitable test system for qualitative and semi-quantitative analysis of anti-pre-S(2) antibodies after hepatitis B vaccination with a higher sensitivity, but probably also a different specificity than the EIA.

HLA linked immune response to S and pre-S2 gene products in hepatitis B vaccination

In order to detect a possible HLA linked genetic control of human immune responses to hepatitis B virus, forty healthy adult persons of the same age typed for HLA-A, -B and -DR antigens, were vaccinated against virus hepatitis B and sequentially tested for anti-HBs and anti-pre-S2 antibodies. They received three injections of Hevac-B Pasteur vaccine, the second 1 month and the third 3 months after the first. Following the third immunization, 38 individuals (95%) had a protective level of anti-HBs antibodies and 17 (42.3%) had a positive level of anti-pre-S2 antibodies. HLA-A11 antigen was significantly more frequent (pc = 0.007) among anti-HBs high responders than low responders. In addition, anti-HBs high responders were more frequently HLA-DR1, and less frequently HLA-DR4 and DR7 positive; corrected values, however, were not significant. Anti-pre-S2 high responders showed an apparent increase of HLA-B7, B14 or DR3 antigens, when compared to low responders (pc not significant).

Naturally occurring antibodies to an epitope on Plasmodium falciparum gametes detected by monoclonal antibody-based competitive enzyme-linked immunosorbent assay

The antibody response to an epitope on gamete antigens of Plasmodium falciparum in persons naturally exposed to malaria has been investigated by competitive enzyme-linked immunosorbent assay. The assay detects antibodies to an epitope on the 48/45-kilodalton (kDa) gamete surface antigen by competition with horseradish peroxidase-labeled monoclonal antibody IIC5-B10. Five sera previously shown to immunoprecipitate the 230- and 48/45-kDa antigens significantly inhibited IIC5-B10 binding to an average of 24.2% of control. The one serum which precipitated only the 48/45-kDa antigen did not inhibit IIC5-B10 binding. For 26 sera which were negative by immunoprecipitation, mean binding in the assay was 112.7% of control (pooled London nonimmune sera). Recognition of both 230-kDa and 48/45-kDa antigens was associated with a titer of 1:9 or greater (reciprocal geometric mean titer, 27.6) for inhibition to more than 2 standard deviations from the mean of the negative sera. The results show that the IIC5-B10 binding site is a naturally immunogenic epitope recognized by the majority of persons who had antibodies to the 48/45-kDa protein. An additional finding was enhancement of binding of IIC5-B10 to an average of 154.4% of control by five sera which recognized only the 230-kDa antigen, presumably due to conformational alteration of the gamete antigen complex.

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.