Hepatitis B surface antigen particles with all four subtypic determinants: point mutations of hepatitis B virus DNA inducing phenotypic changes or double infection with viruses of different subtypes

A meta-analysis on genetic variability of RT/HBsAg overlapping region of hepatitis B virus (HBV) isolates of Bangladesh

Background and aim

Hepatitis B caused by HBV is a serious public health hazard prevalent worldwide including Bangladesh. Few scattered molecular studies of HBV have been reported in Bangladesh. This study aimed to analyze the genetic variability of RT/HBsAg overlapping region of HBV isolates of Bangladesh and determination of correlation among the genotype/serotype and HBsAg escape and/or drug-resistant mutations.

Methods

A total of 97 complete HBsAg sequences of Bangladeshi HBV isolates from 2005 to 2017 from NCBI GenBank were extracted and analyzed using several HBV bioinformatics tools such as Geno2pheno-HBV, HBV Serotyper, HIV-Grade:HBV-Tool, and CLC sequence viewer.

Results

The prevalence of genotypes A, C, and D are 18, 46 and 35% which correspond to serotype adw, adr, and ayw, respectively. The prevalence of HBsAg escape mutations is 51% and most of which (62%) are found in the genotype D followed by 32% in genotype C and 6% in genotype A. Interestingly most (24/36) of the sequences of HBsAg escape mutations contained 128 V mutant which all belongs to only serotype ayw3 (Genotype D). Prevalence of drug-resistant mutations is ~ 11%, most of which are from genotype C (63.64%) and D (36.36%). Lamivudine resistant mutations were found in ~ 11% of sequences followed by Telbivudine 10% and Adefovir 3% where Tenofovir showed susceptibility to all 97 sequences. Moreover, 7 among of 97 sequences showed both HBsAg and drugs resistant mutations and none of them are found due to the same nucleotide substitutions.

Conclusion

There is a strong correlation among the genotype/serotype and HBsAg escape and/or drug-resistant mutations. This meta-analytical review will be helpful for genotype-serotype prediction by PCR-based diagnosis and development of vaccine and/or diagnostic kits, and the treatment against HBV infection in the future.

Investigation of a Novel Hepatitis B Virus Surface Antigen (HBsAg) Escape Mutant Affecting Immunogenicity

Mutation in the hepatitis B virus surface antigen (HBsAg) may affect the efficiency of diagnostic immunoassays or success of vaccinations using HBsAg. Thus, antigenicity and immunogenicity analyses of the mutated HBsAg are necessary to develop novel diagnostic tools and efficient vaccinations. Here, the in vitro antigenicity of three wild-type HBsAg open reading frames (ORFs) (adr4, W1S [subtype adr] and W3S [subtype adr]) isolated from clinically infected patients and nineteen synthesized single/double/multiple amino acid-substituted mutants were tested with commercial ELISA kits. Immunofluorescence staining of transfected cells and Western blot analysis confirmed that these ORFs were expressed at comparable levels in HEK-293 cells. W1S and adr4 were clearly detected, whereas W3S could not be detected. Using the same commercial immunoassay kit, we found that the single mutants, K120P and D123T, were marginally reactive, whereas W3S-aW1S and the double mutant, K120P/D123T, exhibited antigenicity roughly equivalent to the wild-type wako1S. On the other hand, the single mutants of W1S, P120K and T123D, significantly impaired the reactivity, while W1S-aW3S and the double mutant of W1S, P120K/T123D, resulted in a complete loss of antigenicity. In addition, ELISA revealed reduced HBs antigenicity of two mutants, W1S N146G and W1S Q129R/G145R. These commercial ELISA-based antigenic reactivities of HBsAg were also strongly correlated with the predicted Ai alterations of affected amino acids due to the specific mutation. In conclusion, this study showed for the first time that lysine (K120) and aspartate (D123) simultaneously affected HBsAg antigenicity, leading to diagnostic failure. These findings will improve diagnostic assays and vaccine development.

The underlying mechanisms for the "simultaneous HBsAg and anti-HBs serological profile"

The course of HBV infection is determined by the interplay between viral replication via HBV protein production and the host's immune response. Therefore, the diagnosis of infection in clinical practice is established by the serological detection of HBV protein products as well as antibodies produced by the host. Although the serological findings for assessing the clinical course of infection are already well established, the expression of viral proteins and the dynamics of antibody production may vary during the natural course of infection. This causes the HBV infection to be occasionally associated with the presence of unusual serologic profiles, which can lead to doubts in the interpretation of results and mistaken serological diagnosis. The simultaneous detection of HBsAg and anti-HBs in the blood stream comprises an atypical serological profile, somewhat incoherent, whose significance can be complicated to establish. Outlined in this article are some immunological and molecular mechanisms which could justify the existence of this profile in which there is a great laboratorial and clinical interest.

Double hepatitis B virus infection in a patient with HIV/hepatitis C virus coinfection and 'anti-HBc alone' as serological pattern

Reported here is a case of double hepatitis B virus (HBV) infection in an HIV/hepatitis C virus (HCV)-coinfected patient with antibodies against hepatitis B core antigen as the only serological marker (anti-HBc alone). Two different HBV genotypes were identified in this patient. A search of the medical literature indicated this report is the first to describe a multiple silent HBV infection in an HIV/HCV-coinfected-patient. The elevated incidence of the anti-HBc alone pattern in HIV-positive patients and the increasing number of silent HBV infections detected in those patients demonstrate the need to carefully examine HIV-positive patients for occult HBV infection. In addition, it appears necessary to thoroughly study such patients in order to evaluate the impact of mixed HBV infection and triple HIV/HCV/HBV infection on morbidity.

Co-Infection with Hepatitis B Virus Genotype D and Other Genotypes in Western Japan

OBJECTIVE

Genotypes B and C are the prevalent hepatitis B virus (HBV) genotypes in eastern Asia. Although very rare in this region of the world, genotype D was found to be prevalent in a small area of western Japan. In this study, we confirm the frequency and clinical significance of co-infection with different genotypes among patients from that area infected with genotype D.

METHODS

Twenty-three patients from the same area of western Japan infected with HBV genotype D, determined using a genotyping enzyme immunoassay, were studied. Cloning was done using DNA extracted from serum samples, and polymerase chain reaction assays with the restriction fragment length polymorphism for HBV genotyping were performed with 10 clones from each patient.

RESULTS

Four (17.4%) of the 23 patients were found to be co-infected with HBV genotype C, and the HB surface antigen subtype was ayw in both mono- and co-infected patients. No clinical differences were found between mono-infected and co-infected patients carrying genotype D.

CONCLUSION

A significant number of patients from the study area found to be infected with HBV genotype D were co-infected with genotype C. Additional study with a larger number of patients is needed to elucidate the possible clinical significance.

Hepatitis B virus genotypes

Eight genotypes of hepatitis B virus (A-H) are currently recognized, and subgenotypes have recently been described in four of these genotypes (A, B, C and F). The genotypes show a distinct geographical distribution between and even within regions, and are proving to be an invaluable tool in tracing the molecular evolution and patterns and modes of spread of hepatitis B virus. Structural and functional differences between genotypes can influence the severity, course and likelihood of complications, and response to treatment of hepatitis B virus infection and possibly vaccination against the virus. Although the number of studies on these genotypes has increased dramatically during recent years, much remains to be learnt about their full implications.

Hepatitis B virus genotype A and D and clinical outcomes of liver transplantation for HBV-related disease

Hepatitis B virus (HBV) genotypes have been associated with specific patterns of disease and response to antiviral therapy. We investigated the effect of HBV genotype on HBV recurrence and mortality after liver transplantation (LT). Pretransplant sera of 45 hepatitis B surface antigen (HBsAg) positive adults were submitted for HBV genotyping by a reverse-phase hybridization line probe assay with genotype-specific probes. Data were correlated with clinical outcomes after transplantation. Genotype A (n =15), D (n = 13) and A/D (n = 12) accounted for 89% of all genotypes. Coinfection with two HBV genotypes was encountered in 14 (31.1%) patients. Eighteen patients (40 %) developed HBV recurrence at a median of 10 months posttransplant (range, 1-53) and 10 patients (22 %) died at a median of 24 months (range, 3-63). Genotype D patients were more likely to develop HBV recurrence or die compared with genotype A patients, although this did not reach statistical significance. Dual infection with genotype A/D resulted in mortality similar to that of genotype A but recurrence similar to that of genotype D. Active viral replication at time of transplantation was the only independent factor (P = 0.03) that predicted HBV recurrence. In conclusion, HBV genotype A and D did not have a significant impact on clinical outcomes of LT for HBV-related liver disease in patients of European origin. These data do not support routine HBV genotyping in liver transplantation.

Follow up of infection of chacma baboons with inoculum containing a and non-a genotypes of hepatitis B virus

AIM: To determine whether one genotype (A or non-A genotypes of HBV) predominated over the other during the course of HBV infection.

METHODS: Four baboons were inoculated with HBV. DNA was extracted from serum obtained at monthly intervals post-inoculation for 52 weeks and HBV DNA was amplified using primers specific for the core region containing an insert characteristic of genotype A (nt 2354-2359, numbering from the EcoRI site). The amplicons were cloned into PCR-Script^TM and a minimum of 15 clones per time point were sequenced in both directions.

RESULTS: Both genotypes persisted for the entire follow-up period of 52 weeks. Genotype non-A predominated in two baboons and genotype A in one baboon. Neither genotype predominated in the fourth baboon, as shown at a 5% level of testing.

CONCLUSION: No conclusions concerning the dominance of either genotype or the natural progression or replication rates of HBV could be drawn because the pattern of the genotypes found may have been caused by sampling fluctuations at the time of DNA extraction and cloning as a result of the very low viral loads in the baboon sera.

Characterization of two hepatitis B virus populations isolated from a hepatitis B surface antigen-negative patient

In a study of surface antigen-negative, but weakly hepatitis B virus (HBV) DNA-positive, patients, we were able to amplify and clone whole HBV genomes from the serum of a cirrhotic patient. Sequencing showed that the patient harbored two different HBV populations, one of genotype A and the other of genotype D, with the genotype D genome apparently predominating. The surface antigen of the genotype A virus is heavily mutated, especially in the extracellular << determinant a >> region, with several mutations that have not been previously described. The genotype D virus is a precore mutant. Both genomes possess the common A1762T-G1764A double mutation of the basal core promoter (BCP), and the genotype D virus is also mutated in the << TATA box >> of the large surface antigen promoter. Biological characterization showed that the genotype A genome was fully replication-competent, whereas the genotype D genome replicated poorly. The small surface antigen of the genotype A virus was only very weakly recognized by commercial tests. The small surface antigen of the genotype D virus could be recognized by the tests, but it was mainly retained within transfected cells, probably because of an excess of large surface antigen. In conclusion, the cryptic nature of this double HBV infection is characterized by the predominance of the replication-deficient genotype D virus over the replication-competent genotype A virus.

Prevalence of vaccine-induced escape mutants of hepatitis B virus in the adult population in China: a prospective study in 176 restaurant employees

BACKGROUND AND AIM

Hepatitis B virus (HBV) variants with mutations in the S gene would pose a substantial risk to the community as current HBV vaccines are not effective in preventing infection with them. The majority of such vaccine escape mutants so far reported have been found while studying vertical transmission of HBV; the vaccine failure rate in connection with vaccine escape mutants in adults is not clear at the moment. The purpose of this study was to evaluate the efficacy of immunization against HBV in the adult population by analysis using polymerase chain reaction (PCR) to detect HBV-DNA, and also to elucidate the type of mutation encountered in vaccine failure cases.

METHOD

A total of 176 adult restaurant employees in China, who had been vaccinated according to the food epidemic law, were enrolled in a standard vaccination program. Their serum HBV-DNA was determined before and 1 year after the completion of the vaccination program. In those infected with HBV, despite having received the HBV vaccine, direct sequencing within the S gene of the amplified samples was conducted.

RESULTS

Although only two cases were found to be hepatitis B surface antigen (HBsAg) positive 1 year after the completion of the vaccination program, six subjects (3.4%) were found to be HBV-DNA positive assessed by a nested PCR. Four out of these six cases had a point mutation within the 'a' determinant; they were Gly-145-Ala, and Ile/Thr-126-Asn/Ser.

CONCLUSION

The HBV vaccine failure rate assessed by using PCR analysis was 3.4% (six of 176) in the Chinese adult population undergoing the HBV vaccination program. Hepatitis B virus variants with missense mutation within the 'a' determinant were responsible in most cases.

Characterization of hepatitis B virus genotypes among Yucpa Indians in Venezuela

The complete genome sequences of hepatitis B virus (HBV) from 12 HBV-infected Yucpa Indians of Venezuela, a group with highly endemic HBV, were amplified and sequenced. The 12 isolates were closely related to each other, with 98.6-100% nucleotide identity. A phylogenetic tree based on the complete genome indicated clearly that they were genotype F. Three individuals had evidence of infection with two different HBV deletion mutants. In two individuals, a three amino acid deletion was identified just prior to the 'a' determinant loop of the S region. A third individual was infected with virus that contained a complete core reading frame and a population that contained a deletion in the middle of the core region. These results indicate that genotype F HBV is present in the Venezuelan Yucpa Amerindians and the complete genome sequence allowed the identification of two unique deletion mutants in a limited set of samples.

HBsAg subtype distribution among different populations of HBsAg carriers in Spain

Data concerning the HBsAg subtype distribution in Spain are out-of-date and confined to a restricted geographical area. Furthermore, the complex distribution observed in the countries surrounding Spain prevents any prediction. To obtain further data on HBsAg subtype distribution among Spanish HBsAg carriers, subtyping analysis (d and y determinants) was performed in 670 samples from subjects belonging to various epidemiological risk groups and coming from different geographical areas of the country. Similar frequencies were found for both mutually exclusive d/y subtype determinants among non-risk, normal HBsAg carriers from almost all geographical areas studied. In contrast, the ay subtype was clearly predominant (79-87%) among intravenous drug users, irrespective of their geographical origin. Thirteen different institutions for mentally retarded patients behaved as closed communities for HBV circulation, showing independent subtype distributions. Thus, no significant geographical variations were found for HBsAg subtype distribution in Spain. The prevalence of each particular subtype is mainly dependent on the epidemiological characteristics of the carriers studied. Subtype distribution was independent of the presence of HBeAg or HDV infection serum markers when homogeneous groups were considered separately. Atypical HBsAg phenotypes, either with coexistence or absence of both subtype determinants, were found in some cases.

Polymerase chain reaction can resolve some undefined cases of hepatitis B virus antigenic subtyping

HBsAg subtypes were defined by means of adsorbed polyclonal antisera; however, HBsAg subtyping is currently usually carried out with monoclonal antibodies (Mab). We developed a complementary subtyping method based on the polymerase chain reaction. Reference samples belonging to all known HBsAg subtypes could be detected and grouped into four different categories (ayw1/ayw4/ayr, ayw2/ayw3, adw2/adrq+/adrq-, adw4). Thirteen HBsAg-positive serum samples previously subtyped as ad by means of monoclonal antibodies fell into the adw2/adrq+/adrq- group, as well as 13 ay samples into the ayw2/ayw3 group. These results could be confirmed by means of reference polyclonal antisera in nine ad cases (all adw2) and in seven ay cases (all ayw3); the remaining seven were below the detection limit of the polyclonal assay. Four samples which were not recognized by any of the d/y subtype-specific Mab were shown to contain ayw2/ayw3 sequences. Only one contained sufficient HBsAg to be confirmed as ayw3 by means of reference antisera. Three of five sera showing simultaneous reactivity both for d and y-specific Mab were classified as adw4 by PCR, as was one by reference polyclonal antisera. The y-specific monoclonal antibody cross-reacted with the adw4 subtype. Single adw2 sequences were amplified in one of the remaining two cases, as well as single ayw2/ayw3 sequences in the other, suggesting that they showed true coexistence of two strains of different subtype, only one of which was in active replication state. It is concluded that the method described is useful in the solution of some undefined cases obtained with the monoclonal-based assays.

High carrier rate after hepatitis B virus infection in the elderly

An outbreak of hepatitis B virus infection occurred in a nursing facility; it involved 31 patients with sequelae of cerebral vascular accidents (15 men and 16 women; mean age, 77.4 +/- 9.3 yr). HBsAg disappeared within 6 mo in 9 patients and persisted during an observation period of more than 6 mo in 13; the remaining 9 patients were lost to follow-up while they carried HBsAg. Thus 13 of 22 patients followed (59%) became HBsAg carriers. We amplified a part of the S gene (436 nucleotides) with polymerase chain reaction on hepatitis B virus DNA from 12 randomly selected patients. The sequences of nine patients were the same as that of a nursing assistant who was an HBsAg carrier and suspected as the source of infection; it differed by only 1 or 2 (< 0.5%) nucleotides from those of the remaining three patients. Between the group of nine patients with transient HBV infection and the 13 patients with persistent HBV infection, we found no differences in age or sex or in parameters of nutrition or immunocompetence. These results indicate a high incidence of HBV carrier state in the elderly.

Allelic subtypic determinants of hepatitis B surface antigen (i and t) that are distinct from d/y or w/r

A monoclonal antibody (I-18) was raised against an enneapeptide representing amino acids 125 to 133 of the product of the S gene of hepatitis B virus DNA [S(125-133) segment] with a sequence of Thr-Ile-126-Pro-Ala-Gln-Gly-Thr-Ser-Met. Another monoclonal antibody (T-7) was raised against an S(125-133) segment in which Ile-126 was replaced by Thr-126. In a panel of 16 samples of hepatitis B surface antigen (HBsAg) with known S gene sequences, I-18 reacted with 5 with Ile-126. T-7 reacted with 10 HBsAg samples with Thr-126; it did not, however, react with the remaining one of subtype ayw with Thr-126 flanked by Met-125 and Thr-127. The two allelic subtypic determinants, specified by Ile-126 and Thr-126 and distinct from d/y or w/r, were named i and t after isoleucine and threonine, which regulate them. They were expressed in a mutually exclusive fashion in 216 (83%) of 260 HBsAg samples from asymptomatic carriers. They were not detected in 36 (14%) samples; the failure to detect an i or t determinant was particularly common in HBsAg samples of subtype ayw (26 [79%] of 33). A part of the S gene sequence was determined for eight HBsAg samples without a detectable i or t determinant. They had an Ile-126 or Thr-126 residue that was flanked by Thr-127, not the Pro-127 commonly possessed by HBsAg samples displaying an i or t determinant. Expression of the i/t allele, therefore, would require Pro-127. In eight (3%) of the samples, both i and t determinants were detected; the presence of i and t on the selfsame HBsAg particles was verified by sandwiching the particles between I-18 and T-7. A point mutation from thymine to cytosine at nucleotide 377 in the S gene, contributing different second letters to codon 126 (ATT for Ile and ACT for Thr), would have been responsible for the assembly of HBsAg particles with both i and t determinants by means of phenotypic mixing.

Correlation between anti-HBc titers and HBV DNA in blood units without detectable HBsAg

Hepatitis B virus (HBV) DNA was tested for in 294 blood units which had antibody against hepatitis B core antigen (anti-HBc) as the isolated serological marker of HBV infection. After amplification by polymerase chain reaction, HBV DNA was detected in 12 (6.9%) of 175 units that were positive for anti-HBc with hemagglutination inhibition titers greater than or equal to 2(6), significantly more often than in none of 119 units with titers less than or equal to 2(5) (p less than 0.01). These results indicate that the exclusion of blood units with isolated high-titer anti-HBc would be effective for further decreasing the risk of posttransfusion hepatitis B.

Hepatitis B surface antigen particles of subtypes adw and adr, and compound subtype (adwr) in symptom-free carriers in Japan

Of sera from 1,878 Japanese blood donors who carried hepatitis B surface antigen (HBsAg), 420 were subtyped as adw (22.4%) and 1,443 as adr (76.8%); only 15 (0.8%) contained HBsAg of subtype ayw or ayr. Sera with HBsAg/adr had higher HBsAg titres than those with HBsAg/adw (geometric mean of haemagglutination titre: 10.1 +/- 2.4 vs. 9.7 +/- 2.4, p less than 0.01), and a higher prevalence of hepatitis B e antigen (24% vs. 13%, p less than 0.001). Carriers of HBsAg/adr progressively predominated over those of HBsAg/adw with increasing age. Of sera from 1,863 carriers of HBsAg/adw or HBsAg/adr, 182 (9.8%) contained HBsAg particles with both subtypic determinants in the w/r allele. The presence of w and r determinants on the same particles was ascertained by sandwiching them between monoclonal antibody with the specificity for w and that with the specificity for r. HBsAg particles of compound subtype (adwr) were found more often in sera with hepatitis B e antigen than those without it (145/403 [36.0%] vs. 37/1,460 [2.5%], p less than 0.001). Sera with HBsAg/adwr particles had HBsAg titres higher than those without them (12.4 +/- 1.9 vs. 9.7 +/- 2.3, p less than 0.001). HBsAg/adwr particles arise from phenotypic mixing of the S-gene product of wild-type virus and that of mutants with point mutations for subtypic changes. The results obtained indicated that HBV strains of subtype adr have a higher replicative activity than those of adw, and suggested that mutations in the S gene for subtypic changes would be associated with an active replication of hepatitis B virus.

Persistence of hepatitis B viral DNA after serological recovery from hepatitis B virus infection

Chronic hepatitis B virus infection is a major medical problem worldwide. Apart from HBsAg carriers, hepatitis B virus has also been identified in some HBsAg-individuals with or without antibodies to viral antigens. The molecular mechanisms underlying hepatitis B virus persistence in HBsAg-individuals are unresolved, however. To identify a possible genetic basis for viral persistence, we cloned the viral genome from the liver of a patient serologically immune to hepatitis B virus infection. DNA sequence analysis of the complete viral genome identified numerous mutations in all viral genes. Analysis of the biological effects of these mutations revealed three major findings: a low level of HBsAg synthesis, absence of HBeAg production and a defect terminating viral replication. These data suggest that mutations accumulating during the natural course of hepatitis B virus infection may be a mechanism underlying viral persistence in HBsAg-individuals, presumably through escape from immune surveillance.

Expression of hepatitis B surface antigen subtypes in liver of patients with hepatocellular carcinoma; comparison of subtypes in serum and liver

To clarify the discrepancy in hepatitis B surface antigen (HBsAg) subtypes present in the serum and liver, as well as among hepatocytes, liver specimens which were resected from 37 HBsAg-positive patients with hepatocellular carcinoma (HCC) were examined. We evaluated HBsAg and the subtypic determinants of HBsAg and hepatitis B core antigen (HBcAg) using the peroxidase-antiperoxidase (PAP) staining method. Hepatitis B antigens were more frequently detected in small tumors (HBsAg in 67%. HBcAg in 40%) than in large ones (HBsAg in 36%, HBcAg in 14%). The prevalence of each subtypic determinant in the HBsAg positive non-tumorous vs. tumorous areas was 100% vs. 67% in a, 100% vs. 57% in d, 100% vs. not tested in y, 100% vs. 53% in r and 25% vs. 0% in w (a, d, y, r and w represent subtypic determinants). There was virtually no difference in a set of subtypic determinants between the serum and liver. However, there were some variations in a set of subtypic determinants among the hepatocytes. On the other hand, liver tissue of compound subtype adyr in serum contained both cells with a,d,r and with a,y,r as well as a few cells with a,d,y,r. These findings suggest that HBV genomes in hepatocytes of type B chronic liver disease may differ genetically among cells even in the same liver tissue.