Presentation of the hydrophilic domains of hepatitis C Viral E2 envelope glycoprotein on hepatitis B surface antigen particles

Subviral particles of hepatitis B virus have been used to present foreign epitopes. We attempted to present the hydrophilic domains of E2 envelope protein of hepatitis C virus (HCV) as a fusion protein with hepatitis B virus surface antigen (HBsAg). The five hydrophilic domains of HCV E2 antigen were inserted into HBsAg such that the inserted hydrophilic domains were presented on the outer surface of HBV subviral particles. In addition, a fusion encoding the hypervariable region (HVR) of E2 antigen was also made. Cell lysate and culture medium were analyzed for the synthesis and secretion of the fusion proteins by immunoprecipitation with polyclonal anti-HBsAg antibody using recombinant vaccinia virus system. The results showed that the fusion proteins containing these six E2 domains were made in the cell, but only two out of six fusion proteins were secreted into culture medium. Further, cesium chloride density gradient analysis and electron microscopy revealed that these fusions were secreted into culture media as particles. It will be of interest to test immunogenicity of the HBsAg fusion particles containing the HCV E2 domains in animal model. © 1996 Wiley-Liss, Inc.     

Hepatitis C virus is frequently coinfected with serum marker-negative hepatitis B virus: Probable replication promotion of the former by the latter as demonstrated by in vitro cotransfection

Patients with hepatitis C have been reported occasionally to be coinfected with serum marker-negative (silent) hepatitis B virus (HBV). The frequency and significance of such coinfection were investigated. Thirty patients with hepatitis C virus (HCV) infections (10 acute, 10 chronic, 10 cirrhotic) were selected randomly; the acute cases were without serum hepatitis B surface antigen (HBsAg) and anti-hepatitis B core IgM, and the chronic cases were without HBsAg. A nested polymerase chain reaction for the X open reading frame was used to amplify HBV DNA in serum, and immunoperoxidase staining was carried out on liver biopsy specimens. Nucleotide sequencing was carried out to characterize the amplified HBV DNAs. In order to clarify the possibility that the silent HBV mutant promotes HCV replication in the liver, the full-length HCV RNA and the cloned silent HBV DNA dimer were cotransfected into an established cell line, HuH-7, and the amount of secreted HCV RNA was quantified serially. The target HBV DNA was amplified in 26 (86.7%) of the 30 patients. Subsequent direct nucleotide sequencing in 9 selected patients revealed an 8-nucleotide deletion, characteristic of a silent HBV mutant. Immunostaining revealed hepatitis B surface antigen in 15 (50.0%). Cotransfected silent HBV DNA augmented the secretion of HCV RNA by up to 5-fold in comparison with HCV RNA transfection alone. In conclusion, HCV is coinfected frequently with the silent HBV mutant and the latter probably promotes the replication of the former in the liver. J. Med. Virol. 52:399–405, 1997. © 1997 Wiley-Liss, Inc.     

Polyalbumin receptors on hepatitis B virus and on 22 nm hepatitis B surface antigen (HBsAg)2 particles

Receptors for polymerized human serum albumin ( pHSA ) were studied by solid-phase radioimmunoassay on different hepatitis B surface antigen (HBsAg) particles subpopulations prepared both from hepatitis B e antigen (HBeAg) and from anti-HBe-positive sera. HBsAg particles in HBeAg-positive serum showed higher expression of the receptor compared with HBsAg particles from anti-HBe-positive serum. Analysis of different morphological forms of virus particles was performed after separation by density-gradient ultracentrifugation. Maximum receptor expression was detected in HBV particles containing fractions while the 22-nm HBsAg particles had significantly lower receptor activity. These observations support the hypothesis of a pathogenetic role of the pHSA receptor in mediating virus access to hepatocytes. Indeed, the higher pHSA binding activity on HBV particles could allow selective attachment of the infectious virion to liver cells that bear similar albumin receptors on their surface.     

含HPV16 E7的嵌合型VLPs引发细胞溶解反应

目的 探讨ＢＰＶ（牛乳头状瘤病毒）Ｌ１／ＨＰＶ（人乳头状瘤病毒）１６Ｅ７嵌合型乳头状瘤病毒样颗粒（ＶＩＰｓＸ）的免疫学特性。方法 将表达纯化的含ＢＰＶＬ１／ＨＰＶ１６Ｅ７的嵌合型ＶＬＰｓ作为抗原在体外刺激ＥＬ－４细胞并对其进行细胞毒性Ｔ淋巴细胞（ＣＴＬ）反应分析。结果 嵌合型ＶＬＰｓ可引发特异的ＣＴＬ反应。Ｌ１－ＶＬＰｓ抗体能阻断这种特异性细胞溶解反应。结论 含ＢＰＶＬ１／ＨＰＶ１６Ｅ７嵌合型的Ｖ     

Tubular forms of hepatitis b surface antigen bind with the nucleus of 22-nm spherical hbsag particles

Spherical hepatitis B surface antigen particles (HbsAg) of 22-nm diameter were treated with sodium dodecylsulphate in the absence of reducing agents, and their nuclei were exposed. Factors that interact with the nucleus of HbsAg were detected in the serum of HBsAg carriers who were seropositive for hepatitis B e antigen and identified as tubular forms of HBsAg. The other categories of hepatitis B antigen, Dane particles, and 22-nm spherical HBsAg did not bind with the nucleus of HBsAg. When tubular forms of HBsAg had been treated with a proteolytic enzyme, they lost the reactivity to bind with the nucleus of HBsAg. On the basis of the results obtained, tubular forms of HBsAg bear the receptor of protein nature for the nucleus of 22-nm spherical HBsAg. The receptor allows rapid determination of tubular forms by a haemagglutination method for the evaluation of their clinical and epidemiological implications.     

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.     

Secretion of polyalbumin receptors in vitro

The nature of hepatitis B surface antigen (HBsAg)-associated receptors for polymerized human serum albumin (pHSA-R) and their relationship to hepatitis B e antigen (HBeAg) and human serum proteins have not been defined. We studied by radioimmunoassay and by electron microscopy HBsAg-associated pHSA-R secreted in vitro by a human hepatocellular carcinoma cell line (PLC/PRF/5) and by mouse 3T3 fibroblasts after transfection with cloned hepatitis B virus (HBV) DNA (4.10 cells). PLC/PRF/5 cells expressed only HBsAg, whereas 4.10 cells secreted also HBeAg. There was no significant difference in the production of HBsAg, HBeAg, and pHSA-R when the cells were cultured in the presence or absence of fetal calf serum. Secretion of pHSA-R by the two cell lines for a given amount of HBsAg was equal irrespective of the presence or absence of HBeAg. Supernatants from both cell lines grown in serum-free medium did not contain any Clq or albumin when tested by immunodiffusion. The ability of a transfected mouse cell line to produce HBsAg with pHSA-R activity strongly suggests that pHSA-R is coded by the HBV genome and does not depend on the presence of human serum proteins. In addition, our findings fail to demonstrate any correlation between HBeAg production and pHSA-R.     

Discrepancy between Serological and Virological Analysis of Viral Hepatitis in Hemodialysis Patients

Background and Aim: Viral hepatitis is a health threat for hemodialysis (HD) patients and it may be transmitted during treatment. Some patients categorized to have viral hepatitis were found to be non-viremic. To clarify the discrepancy between the serological tests in HD patients, we conducted the study.Methods: A total of 1681 HD patients was included. Blood samples were analyzed for hepatitis B surface antigen (HBsAg) and anti-hepatitis C antibody (anti-HCV). Detection of hepatitis B virus (HBV) DNA and hepatitis C virus (HCV) RNA were performed in either HBsAg (+) or anti-HCV (+) samples. HBV DNA/HCV RNA was also measured in a subset of HBsAg (-) and anti-HCV (-) patients. Liver function tests were analyzed and compared with the serological and virological tests.Results: The serological tests showed that 230 patients (13.7%) were HBsAg (+) and 290 (17.3%) were anti-HCV (+). We were unable to detect HBV DNA in 97 of 230 (42.2%) HBsAg (+) patients, and HCV RNA could not be found in 76 of 290 (26.2%) anti-HCV (+) patients. In 167 HBsAg (-) patients, only one showed a trace amount of HBV DNA. None of 151 anti-HCV (-) patients showed detectable HCV RNA. The prevalence rate of viral hepatitis remains high in Taiwanese HD patients: 13.7% for HBV and 17.3% for HCV. However, virological analysis showed 42.2% non-viremic rate for HBsAg and 26.2% non-viremic rate for anti-HCV.Conclusions: The findings might challenge the presently suggested principles of bed and machine dedication and the diagnosis of viral hepatitis in HD patients.     

Immunoreactivity of HCV/HBV epitopes displayed in an epitope-presenting system

It has been demonstrated that the immunodominant region of the HCV core protein and the hepatitis B surface antigen (HBsAg) have high degree of reactivity. In order to construct a chimeric protein that carries HCV and HBV epitopes and possesses immunogenicity to both HCV and HBV, four epitopes derived from residues aa2-21 (epitope C1), aa22-40 (epitope C2) of the core protein, residues aa315-328 (epitope E) of E1 protein of HCV, and residues aa124-147 (epitope S) of HBsAg were chosen to be displayed in a conformation-specific manner on the outer surface of the Flock House virus capsid protein and expressed in E. coli cells. The reactivity of these epitopes with antisera from hepatitis C and hepatitis B patients and induction of immune response in guinea pigs were determined. The results showed that when displayed in this system, the chimeric protein carrying only epitope S could react with anti-HBsAg positive human sera, elicit an anti-HBsAg response in guinea pigs. The chimeric protein carrying epitopes C1, C2 and E could react with antibodies to different HCV genotypes, elicit an anti-HCV response in guinea pigs. The chimeric protein carrying epitopes C1, C2, E, and S could react with antibodies against HCV and HBV, elicit anti-HCV and anti-HBsAg responses in guinea pigs. The results suggested that these epitopes displayed in this form could be considered for development of epitope-based vaccines against HCV/HBV infections.     

Co-occurrence of HBsAg and anti-HBs: Two consecutive infections or a sign of advanced chronic liver disease?

Simultaneous presence of hepatitis B surface antigen (HBsAg) and antibodies to the surface antigen (anti-HBs) was detected in 32 out of 89 Dutch chronic hepatitis patients of Caucasian race. HBsAg was subtyped ad in 28 and ay in four cases. Anti-HBs could be subtyped in 25 cases using reference antigens discriminating between d, y, and w1-4 subdeterminants. In 20 patients HBsAg subtype ad (HBsAg/ ad) was accompanied by antibody to subdeterminant y (anti-y), whereas HBsAg/ ay and anti-d were simultaneously detected in the serum of one patient. The antibody pattern in sera from the remaining patients was complex. Eighteen anti-HBs-positive patients were matched for age, histology, and hepatitis B e antigen (HBeAg) status with 18 anti-HBs-negative patients. Differences in risk factors for acquiring a hepatitis B infection were not found. These results do not support the hypothesis that co-occurrence of HBsAg and anti-HBs is due to two consecutive infections with hepatitis B virus. The frequency of the co-occurrence of HBsAg and anti-HBs was found to be related to the degree of progressive liver disease, since anti-HBs was found in three out of 23 asymptomatic carriers, in four out of 20 chronic persistent hepatitis patients, in 20 out of 41 chronic active hepatitis patients, and in all five patients with chronic active hepatitis and cirrhosis. The high frequency of anti-HBs in advanced liver disease may be the result of a disturbed immunologic response mechanism.     

e抗原阳性慢性乙型肝炎患者血清HBV-DNA与HBsAg、HBeAg的相关性分析

目的 研究e抗原阳性慢性乙型肝炎患者外周血中HBV-DNA载量与乙型肝炎病毒表面抗原（HBsAg）、乙型肝炎病毒e抗原（HBeAg）的相关性,及其在不同性别、年龄群体中的差异.方法 收集319例e抗原阳性慢性乙肝患者血清,采用实时荧光定量PCR法检测HBV-DNA载量,用时间分辨免疫荧光法检测HBsAg和HBeAg的浓度,利用SPSS软件做统计分析.结果 HBV-DNA载量与HBsAg含量有良好的相关性（r=0.514,P〈0.001）;与HBeAg含量有相关（r=0.337,P〈0.001）;女性的HBeAg水平要高于男性患者（P〈0.05）;年龄（31～50）岁组、〉50岁组的HBV-DNA、HBsAg 及HBeAg值皆高于年龄 〈30岁组 （P〈0.001）.结论 e抗原阳性慢性乙型肝炎患者血清中HBV-DNA载量与HBsAg、HBeAg定量水平皆有相关性,其中与HBsAg相关性更佳.     

Low-Level Viremia and Intracellular Expression of Hepatitis B Surface Antigen (HBsAg) in HBsAg Carriers with Concurrent Hepatitis C Virus Infection

Assays of hepatitis B virus (HBV) replication and antigen expression in HBV surface antigen (HBsAg) carriers with concurrent hepatitis C or D virus (HCV or HDV) infection revealed that HCV and HDV can suppress HBV replication but that HCV also substantially suppresses HBV surface protein expression. HBsAg carriers with concurrent HCV infection thus have low-level viremia and intracellular HBsAg.     

Hepatitis C virus antibody in hepatocellular carcinoma in Taiwan.

The prevalence of antibody to hepatitis C virus (anti-HCV) was investigated in patients with hepatocellular carcinoma (HCC), and correlated with the clinical features. Anti-HCV was detected in 129 histology or aspiration cytology proven HCC patients and 54 healthy controls. Anti-HCV was examined by the HCV EIA (Abbott Laboratories). All healthy controls were anti-HCV-negative. Nineteen of 81 (23.5%) hepatitis B surface antigen (HBsAg)-positive HCC patients were positive for anti-HCV. Anti-HCV was found among 60.4% (29/48) of HCC patients without detectable HB-sAg. Forty-eight of 129 (37.2%) HCC patients were positive for anti-HCV. There was a significant difference in the prevalence of anti-HCV between patients with HBsAg (23.5%) and those without HBsAg (60.4%, P = 0.0001). However, irrespective of the status of HBsAg, there was no statistical difference in sex, age, routine liver function tests, alpha-fetoprotein concentration, or associated cirrhosis between patients with anti-HCV and those without. The results imply that hepatitis C virus may play a role in the pathogenesis of HCC.     

Serological markers of hepatitis B, C, and E viruses and human immunodeficiency virus type-1 infections in pregnant women in Bali, Indonesia

Except for hepatitis B virus (HBV), there have been few data on serological markers of hepatitis viruses such as hepatitis C virus (HCV) and E virus (HEV), and human immunodeficiency virus type-1 (HIV) in Bali, Indonesia. During 5 months from April to August 2003, sera were collected from 2,450 pregnant women at eight jurisdictions in Bali, and they were tested for markers of these viruses. Only one (0.04%) was positive for antibody to HCV, but none for antibody to HIV. Hepatitis B surface antigen (HBsAg) was detected in 46 (1.9%) at a prevalence significantly lower than that in 271 of the 10,526 (2.6%) pregnant women in Bali surveyed 10 years previously (P < 0.045). The prevalence of hepatitis B e antigen in pregnant women with HBsAg decreased, also, from 50% to 28% during the 10 years (P < 0.011). Antibody to HEV (anti-HEV) was examined in 819 pregnant women who had been randomly selected from the 2,450. The overall prevalence of anti-HEV was 18%, and there were substantial regional differences spanning from 5% at Tabanan district to 32% at Gianyar district. Furthermore, the prevalence of anti-HEV differed substantially by their religions. In the Sanglah area of Denpasar City, for instance, anti-HEV was detected in 20 of the 102 (20%) Hindus, significantly more frequently than in only 2 of the 101 (2.0%) Muslims (P < 0.001). Swine that are prohibited to Muslims, therefore, is likely to serve as a reservoir of HEV in Bali. In conclusion, HBV is decreasing, HCV and HIV have not prevailed, as yet, while HEV is endemic probably through zoonotic infection in Bali.     

Unidentified virus-like particles are detected in plasmas with elevated ALT levels: are they significant of etiological agent(s) of non-B,non-C hepatitis?

GB virus C (GBV-C) and hepatitis G virus (HGV) have been proposed as new viruses etiologically implicated in non-B, non-C hepatitis, but the morphology of these particular virus particles is still unknown, and most cases of non-A to E hepatitis do not relate to their infections. We tried to visualize virus-like particles (VLPs) in plasma samples from hepatitis B surface antigen- and antibody to hepatitis C virus (HCV)-negative blood donors with elevated alanine aminotransferase (ALT), and examined the association of the virus-like particles and the genomes of parenterally transmissible GBV-C/HGV. Twenty-three plasma samples, 13 with elevated ALT levels and 10 with normal ALT values, from blood donors without infections of hepatitis B virus (HBV) and HCV, were subjected to a 20%–60% sucrose density gradient centrifugation, and virus-like particles were observed by electron microscopy. GBV-C/HGV RNAs in the plasmas were tested. Virus-like particles were found in the fractions with densities of 1.15–1.16 g/ml from 12 of 13 (92.3%) plasmas with elevated ALT levels and 1 of 10 (10%) normal controls. The ultrastructural morphology of visualized VLPs was pleomorphic in size and appearance; the majority of the VLPs were 50- to 80-nm spherical particles with a 35- to 45-nm inner core and 9- to 12-nm-long surface spikelike projections. Rodlike VLPs 50–70 nm in diameter with a length of 110–160 nm were also observed in the same samples. The incidence of detection of the circulating VLPs was significantly (P < 0.001) related to elevated ALT levels, but GBV-C/HGV RNAs were detected in none of the plasmas containing the virus-like particles. Spherical VLPs are detected in HBV- and HCV-negative plasmas significantly correlated with the elevation of ALT, suggesting that they are implicated in non-B, non-C hepatitis.     

Effects of hepatitis C and B viruses infection on the development of hepatocellular carcinoma

A case control study consisting of 102 patients with HCC, 102 sex-matched and age-matched patients with nonhepatic disease, and 204 matched healthy controls was carried out to investigate the effect of hepatitis B virus (HBV) and hepatitis C virus (HCV) infection on the development of hepatocellular carcinoma (HCC). The prevalence of antibody to HCV (anti-HCV) in HCC (34.3%) was higher than in nonhepatic disease (10.7%, P< 0.001) or in healthy controls (2.4%, P< 0.001). The prevalence of hepatitis B surface antigen (HBsAg) in HCC (77.4%) was higher than in nonhepatic disease (16.6%, P< 0.001) or in healthy controls (19.6%, P< 0.001). Anti-HCV positivity in nonhepatic disease was higher than in healthy controls (P<0.01). Using patients with nonhepatic disease as controls, stepwise logistic regression analysis indicated that both anti-HCV (odds ratio, 3.4; 95% confidence interval, 2.1-5.6) and HBsAg (odds ratio, 5.6; 95% confidence interval, 3.6–8.5) are independent risk factors for HCC. Using healthy controls, the development of HCC was also strongly associated with anti-HCV (odds ratio, 8.0; 95% confidence interval, 4.3–14.6) and HBsAg (odds ratio, 5.5; 95% confidence interval, 3.7–8.2). Calculation of incremental odds ratio indicated that there is no interaction between HBV and HCV. In conclusion, HBV and HCV are risk factors of HCC. They act independently and without interaction. © 1994 Wiley-Liss, Inc.     

Proteomic analysis of hepatitis B surface antigen positive transgenic mouse liver and decrease of cyclophilin A

The small, 22-nm spherical particles associated with hepatitis B infection are composed of hepatitis B surface antigen (HBsAg) and usually outnumber the virions by a ratio of 10(2) or 10(3). To study the interactions and pathogenesis between liver cells and the expression of HBsAg, global protein profiles were compared by two dimensional gel-based differential proteomics between the livers of a lineage of HBsAg positive transgenic mice and their HBsAg negative control siblings. A total of 93 proteins were identified in the HBV transgenic mice. Around 45% of these differentially expressed proteins were enzymes associated with metabolism, suggesting that the processing of lipids, carbohydrates and certain amino acids were up- or down-regulated. Among these proteins, cyclophilin A (CypA), the major target for the potent immunosuppressive drug cyclosporin A, was found decreased in HBsAg positive transgenic mouse liver and in a stable cell line expressing HBsAg when compared to their controls. The decrease of intracellular CypA was accompanied by an increased secretion of this protein into the supernatant of HBsAg positive cells. Possible implications of HBsAg expression and the intracellular decrease of CypA are discussed.     

Radioimmunometric assay for hepatitis B surface antigen on the surface of infected cells

It has been difficult to differentiate hepatitis B surface antigen (HBsAg) on the cell surface from intracellular or intramembranous HBsAg that is not exposed to the host immune response. We describe here a radioimmunometric assay for HBsAg on the cell surface using HBsAg producing hepatocellular carcinoma cell lines and fibroblasts transfected with cloned hepatitis B virus DNA as models. The assay is sensitive, specific, simple and takes approximately 1 1/2 h. The procedure may be modified to compare quantitatively cell surface with intracellular HBsAg and to demonstrate other cell associated hepatitis B virus antigens such as HBcAg and HBeAg.     

Hepatitis B and D virus infection among drug abusers in Taiwan

Approximately 15 to 20% of the general population in Taiwan are chronic hepatitis B surface antigen (HBsAg) carriers. However, the incidence of hepatitis D virus (HDV) infection is low (5-8%) in patients with HBsAg-positive chronic liver diseases in this area. To evaluate the prevalence of hepatitis B virus (HBV) and HDV infection among drug abusers in Taiwan, serum samples were collected from 152 drug abusers at the Taipei Municipal Anti-Narcotic Institute and test for HBV and HDV markers. Of these, 24 (15.8%) were HBsAg positive, and only 15 (9.9%) were seronegative for all HBV markers. Of the 115 intravenous drug abusers, serum antibody to hepatitis D antigen (anti-HD) was positive in 78.9% of 19 persons who were HBsAg positive, and in 7.5% of 80 persons who were positive for antibody to HBsAg (anti-HBs). Anti-HD was not detected in the sera from all 37 nonintravenous drug abusers regardless of the status of their HBV markers. Also, none of 63 asymptomatic HBsAg carrier pregnant women or 23 patients with acute type B viral hepatitis had measurable anti-HD in their sera. Thus, the high frequency of HDV detected among Chinese HBsAg carrier intravenous drug abusers in Taiwan is similar to that reported in Western countries.     

Improved Humoral and Cellular Immune Responses Against the gp120 V3 Loop of HIV-1 Following Genetic Immunization with a Chimeric DNA Vaccine Encoding the V3 Inserted into the Hepatitis B Surface Antigen

The gp120-derived V3 loop of HIV-1 is involved in co-receptor interaction, it guides cell tropism, and contains an epitope for antibody neutralization. Thus, HIV-1 V3 is an attractive vaccine candidate. The V3 of the MN strain (MN V3) contains both B- and T-cell epitopes, including a known mouse H-2^d-restricted cytotoxic T lymphocyte (CTL) epitope. In an attempt to improve the immunogenicity of V3 in DNA vaccines, a plasmid expressing MN V3 as a fusion protein with the highly immunogenic middle (pre-S2 + S) surface antigen of hepatitis B virus (HBsAg) was constructed. Epidermal inoculation by gene gun was used for genetic immunization in a mouse model. Antibody and CTL responses to MN V3 and HBsAg were measured and compared with the immune responses obtained after vaccination with plasmids encoding the complete HIV-1 MN gp160 and HBsAg (pre-S2 + S), respectively. DNA vaccination with the HIV MN gp160 envelope plasmid induced a slow and low titred anti-MN V3 antibody response at 12 weeks post-inoculation (p.i.) and a late appearing (7 weeks), weak and variable CTL response. In contrast, DNA vaccination with the HBsAg-encoding plasmid induced a rapid and high titred anti-HBsAg antibody response and a uniform strong anti-HBs CTL response already 1 week p.i. in all mice. DNA vaccination with the chimeric MN V3/HBsAg plasmid elicited humoral responses against both viruses within 3–6 weeks which peaked at 6–12 weeks and remained stable for at least 25 weeks. In addition, specific CTL responses were induced in all mice against both MN V3 and HBsAg already within the first 3 weeks, lasting at least 11 weeks. Thus, HBsAg acts as a ‘genetic vaccine adjuvant’ augmenting and accelerating the cellular and humoral immune response against the inserted MN V3 loop. Such chimeric HIV–HBsAg plasmid constructs may be useful in DNA immunizations as a ‘carrier’ of protein regions or minimal epitopes which are less exposed or poorly immunogenic.