Chimeric hepatitis A virus particles presenting a foreign epitope (HIV gp41) at their surface

Hepatitis A virus (HAV) protein 2A has been demonstrated to be involved in virus morphogenesis and suggested to be located on the surface of the particle. To determine whether this protein can function as a target structure to harbor and expose foreign epitopes on HAV particles, a full-length HAV cDNA, containing a seven amino acid stretch of human immunodeficiency virus type 1 (HIV-1) envelope protein gp41, was constructed. Following vaccinia virus MVA-T7-mediated expression of the cDNA in COS7 and Huh-T7 cells, chimeric HAV particles, exposing the foreign epitope gp41 on their surface, were produced. These particles were found to be empty capsids (70S), as judged by immunospecific enzyme linked immunosorbent assay (ELISA) on sucrose gradient fractions and immunoelectron microscopy. The immunological detection of VP1-2A harboring the gp41 epitope of HIV suggests that the 2A domain of HAV is suitable to present foreign antigenic epitopes.

Experimental hepatitis A virus (HAV) infection in Callithrix jacchus: early detection of HAV antigen and viral fate

Common marmosets (Callithrixjacchus) were orally inoculated with a Brazilian strain (HAF-203) of hepatitis A virus (HAy). Three monkeys were euthanized at postinoculation hours 6, 12 and 24 to investigate the early events of HAV infection. Following others three inoculated and one control marmosets remained throughout the 46 day to evaluation of viral excretion. Different samples were collected to detect sequential presence of HAV RNA by nested reverse transcription-polymerase chain reaction (RT-PCR) in liver, saliva, bile and stools at 6 hours to 461h days postinoculation. Liver tissues were examined by immunofluorescence assay in a confocal laser-scanning microscope for the presence of HAV antigen. HAV RNA was detected in saliva during the course of the study, in bile from 24 hours to 46 days. in stools from 7 to 46 days and liver at 12 hours postinfection. In immunofluorescence of liver stained preparations, viral antigen was present at six hours after inoculation throughout the remainder of the 46-day study. The animals developed histological and biochemical acute hepatitis after second week postinoculation. Spleen, duodenum, and mesenteric lymph nodes specimens were negative for HAV antigens. This study supports the possibility that in Callithrixjacchus orally inoculated with hepatitis A virus the saliva route may be additional way of viral elimination. The viral replication in the liver was responsible for biliary HAV presence and latter HAV detection in fecal samples.

Immunopotentiating reconstituted influenza virosomes as a novel antigen delivery system

Using immunopotentiating, reconstituted influenza virosomes (IRIV) as a delivery vehicle, a number of vaccines have been developed. In humans, IRIV-based vaccines containing hepatitis A and influenza antigens have been found to possess enhanced immunogenicity compared to alum-adsorbed vaccine for hepatitis A or commercial subunits or whole virion influenza vaccines. These vaccines were safe and did not engender any anti-phospholipid antibodies against the liposome components of the IRIV. Hepatitis B, tetanus toxoid and diphtheria toxoid, and nucleic acids have also been incorporated into IRIVs. These vaccines are now undergoing clinical phase I testing. IRIVs are also being evaluated in phase I trials for their ability to deliver antigens by the intranasal route.

Electron microscopy of buffalo green monkey kidney cells persistently infected with hepatitis A virus and immunolocalization of HAV antigens

Studies were carried out to analyse the ultrastructural changes and the distribution of hepatitis A virus (HAV)/antigens at subcellular level in buffalo green monkey kidney (BGMK) cells persistently infected with HM-175 strain of HAV. HAV infected BGMK cells showed distinct abnormalities in the endoplasmic reticulum and cytoplasmic membrane as compared to uninfected cells. The abnormalities were characterized by wavy arrays, structures like myelin, annulate lamellae, cytoplasmic inclusion bodies and vesicles. The wavy arrays within the cytoplasm of the host cells appeared to represent degenerating membranes. A complex myelin like body was found in close association with a group of virus like particles. Annulate lamellae like structures involving single paired membrane were detected infrequently whereas the cytoplasmic vesicles were numerous in these cells. An indirect immunogold technique was utilized to localize the HAV antigenin infected cells. A high density immunogold label for HIV like particles was predominantly detected in cytoplasmic vesicles. These results suggest a strong association of membrane substructure in vesicle forms with the compartmentalized replication of HAV within persistently infected host cells.

A two dose schedule for combined hepatitis A and hepatitis B vaccination in children ages one to eleven years

RATIONALE

A combined hepatitis A and B vaccine, Twinrix, containing at least 720 enzyme-linked immunosorbent assay units of hepatitis A antigen and 20 microg of hepatitis B antigen in the adult formulation and half those doses in the pediatric formulation, has been available in many countries since 1997. This vaccine is administered on a three dose schedule: 0, 1 and 6 months. A reduction in the number of doses would add convenience for the vaccinees and reduce administration-associated costs. We investigated the safety and immunogenicity profile of the adult formulation administered at 0 and 6 months in children ages 1 to 11 years.

METHODS

A total of 237 children of both sexes were enrolled. Blood sampling was performed at 0 and 1, 2, 6 and 7 months. Seropositivity for anti-hepatitis A virus was defined as > or = 33 mIU/ml and seroprotection against hepatitis B virus as > or =10 mIU/ml. Data on solicited and unsolicited adverse events were collected on diary cards.

RESULTS

The vaccine was well-tolerated in all subjects. At Month 7 all subjects had seroconverted for anti-hepatitis A virus antibodies with a high geometric mean concentration (11 543 mIU/ml). We observed a continuous increase in anti-hepatitis B surface antibody (anti-HBs) seroconversion rates and seroprotection rates until Month 6. After the second dose (Month 7), all subjects seroconverted for anti-HBs antibodies with a high geometric mean concentration (8056 mIU/ml) and 98.5% of the subjects were considered seroprotected.

CONCLUSION

The two dose adult formulation could be an alternative to prevent hepatitis A and hepatitis B infection in children ages 1 to 11 years.

Use of linear and multiple antigenic peptides in the immunodiagnosis of acute hepatitis A virus infection

The reactivities of two panels of anti-HAV human sera from geographically distinct areas (Chile and Spain) to synthetic peptides from the VP1, VP2 and VP3 hepatitis A virus capsid proteins were examined by an enzyme-linked immunosorbent assay (ELISA) procedure. Two and four branched multiple antigenic peptides (MAPs) and palmitoylated peptides were compared with free synthetic sequences for the detection of IgM anti-HAV antibodies in the two panels of human sera. Our results showed that acute hepatitis A patient sera recognized preferentially homogeneous two branched MAPs and palmitic acid conjugated peptides. The palmitoyl-derived VP3(110-121) peptide and the corresponding dimeric MAP were the most sensitive and appropriate for serological studies of HAV-infected patients by ELISA, sensitivity and specificity being higher than 90% and 95%, respectively. These peptide-based tests open up new avenues in the development of peptide-based immunosorbent assays for the detection of acute HAV disease.

Recombinant hepatitis A virus antigen: improved production and utility in diagnostic immunoassays

Hepatitis A virus (HAV) immunoassays use cell culture-derived HAV antigen to detect HAV-specific antibodies. The current method of production of HAV antigen in tissue culture is time-consuming and expensive. We previously expressed the HAV open reading frame in recombinant vaccinia viruses (rV-ORF). The recombinant HAV polyprotein was accurately processed and was assembled into subviral particles. These particles were bound by HAV-neutralizing antibodies and were able to elicit antibodies which were detected by commercial immunoassays. The present investigation compared the production of HAV antigen by standard tissue culture methods to the production of HAV antigen with the recombinant vaccinia virus system. In addition, HAV and rV-ORF antigens were assessed for their utility in diagnostic immunoassays. Serum or plasma samples from HAV antibody-positive and antibody-negative individuals were evaluated by immunoassay that used either HAV or rV-ORF antigen. All samples (86 of 86) in which HAV antibody was detected by a commercial enzyme-linked immunosorbent assay (ELISA) also tested positive by the recombinant antigen-based immunoassay (VacRIA). Similarly, all samples (50 of 50) that were HAV antibody negative also tested negative by the VacRIA. The lower limit of detection of HAV antibody was similar among immunoassays with either HAV or rV-ORF antigen. Thus, in the population studied, the sensitivity and specificity of the VacRIA were equivalent to those of the commercial ELISA. Since production of recombinant antigen is faster and less expensive than production of traditional HAV antigen, the development of diagnostic HAV antibody tests with recombinant HAV antigen appears warranted.

[Monoclonal antibodies in human hepatitis A virus immunoenzyme diagnosis]

Antigen and antibody detection in EIA is a good tool in diagnosing HAV infections, especially in their differentiation from other hepatitides. Commercial kits containing polyclonal antibodies and murine MAbs to identify HAV are now available. Rat MAbs have not been assayed so far. Peroxidase-labelled rat MAbs and purified rat MAbs as antigen capture were used to modify commercial "VectoHep A-IgM" and "VectorHep A-Ag" kits. The results obtained with modified "VectoHep A-IgM" and "VectorHep A-Ag" kits with labelled rat MAbs suggest that labelled rat MAbs can increase the sensitivity and specificity of EIA. MAbs used as antigen capture and labelled antibodies permit at least an 8-fold increase in sensitivity as compared to polyclonal antibodies. The modified "VectorHep A-Ag" kit with labelled rat MAbs provided 100% sensitivity and specificity in EIA. The modified "VectorHep A-Ag" kit also allowed the authors to determine viral antigens in the cell lysate, homogenates of the infected monkey liver, stools from patients, and sewage water samples. The rat MAbs modified kits can be recommended for using in epidemiological and clinical studies of HAV infections.

Single-antibody in situ enzyme immunoassay for infectivity titration of hepatitis A virus

Hepatitis A virus (HAV) establishes a persistent infection in cultured cells, with minimal effect on host cell metabolism. As a result, the virus produces very little, if any, cytopathic effect (CPE), even with cell culture-adapted strains. This feature precludes the use of a plaque or standard endpoint assay (using CPE as an indicator of infection) for the titration of infectious virus. The radioimmunofocus assay (RIFA) is the standard method for HAV titration, though this method is labour intensive and requires the use of radioisotopes. To this end, a single-antibody in situ enzyme immunoassay (EIA) has been developed, using binding of a perioxidase-labelled monoclonal antibody to fixed cell monolayers as an indicator of infection. This novel assay is highly reproducible, can be read by eye, and is suitable for high throughput situations. Furthermore, the assay has been validated against the RIFA making it suitable for use in studies validating the safety of therapeutic biologicals for human use.

Luminescent oxygen channeling assay (LOCI): sensitive, broadly applicable homogeneous immunoassay method

Luminescent oxygen channeling assay (LOCI) is a homogeneous immunoassay method capable of rapid, quantitative determination of a wide range of analytes--including high and very low concentrations of large and small molecules, free (unbound) drugs, DNA, and specific IgM. Assays have been carried out in serum and in lysed blood. Reliable detection of 1.25 microU/L thyrotropin (TSH) and 5 ng/L hepatitis B surface antigen (HBsAg) corresponds to detection limits approximately 3- and approximately 20-fold lower, respectively, than those of the best commercially available assays. An assay of chorionic gonadotropin is capable of quantification over a 10(6)-fold range of concentrations without a biphasic response. Latex particle pairs are formed in the assay through specific binding interactions by sequentially combining the sample and two reagents. One particle contains a photosensitizer, the other a chemiluminescer. Irradiation causes photosensitized formation of singlet oxygen, which migrates to a bound particle and activates the chemiluminescer, thereby initiating a delayed luminescence emission. Assay times range from 1 to 25 min.

Inhibition of the expression of hepatitis A and B viruses (HAV and HBV) proteins by interferon in a human hepatocarcinoma cell line (PLC/PRF/5)

AIMS/METHODS

PLC/PRF/5 is a continuous human hepatocarcinoma cell line whose genome contains integrated HBV DNA and which secretes two of the hepatitis B virus envelope proteins (HBs and PreS2). This line is also susceptible to infection by hepatitis A virus and was therefore used to compare the effects of interferon on protein synthesis of these two viruses and to assess the interactions which occur between them during infection.

RESULTS

Results showed that recombinant interferon alpha 2-a inhibited the expression of the two hepatitis B virus envelope antigens (HBs and PreS2) and of the only hepatitis A virus antigen in a dose-dependent fashion. Comparison of the effect of interferon on antigenic protein production of these two viruses, showed stronger inhibition of hepatitis A virus capsid antigen than of hepatitis B virus envelope antigens. Infection with hepatitis A virus also downregulates the expression of the two hepatitis B virus proteins.

CONCLUSIONS

Considering the absence of cytotoxic effects from the doses used, this study confirms the relevance of this cellular model for the study of antiviral cytokines in vitro. It also provides a further rationale for the clinical evaluation of the therapeutic potential of interferons in severe hepatitis cases due either to hepatitis A virus alone or to superinfection of hepatitis B virus carriers by hepatitis A virus.

[Concentration of hepatitis A and B virus antigens using water-soluble polymers]

A possibility of using reversibly sedimented polymeric system for the concentration of hepatitis A and B virus antigen has been demonstrated. As polymeric systems, tetrasole-containing polyelectrolytes and interpolymeric complex polymethacryl acid-poly-1-vinylpyrrolidone were used, capable of sedimenting in acid medium and dissolving in media with the neutral pH.

Hepatitis A vaccination by intracutaneous low dose administration: a less expensive alternative

We investigated the immune response to three different intracutaneous (i.c.) doses of inactivated hepatitis A vaccine: 72, 144, and 216 ELISA units (EU). The response was measured using a quotient score derived from a commercial enzyme-linked immunosorbent assay (HAVAB Abbott) and translated to IU per liter using a World Health Organization standard serum for hepatitis A virus antibody. The results were compared with the results obtained after an intramuscular (i.m.) full dose, i.e. 1,440 EU, at 0 and 6-12 months. As estimated from antibody concentration, 3 lots of 144 EU i.c. with 100% or two lots of 216 EU i.c. with 98% seroconversion results in at least as good early protection as the standard immunization with one lot of 1,440 EU i.m., (79% with our method). Indeed, only two doses of 144 EU vaccine (90% seroconversion) seem to give results comparable to the standard procedure. After the booster dose the median antibody concentration is 1,290 IU/l for the 144 EU vaccine and 837 for the 216 EU one, compared with an antibody response of 990 IU/l for the standard 1,440 EU i.m. vaccination. In conclusion, three doses of 144 EU vaccine i.c. or, as an alternative, two doses of 216 EU at monthly intervals give good early protection (e.g. before travel). After the booster dose, which is given 6 months to 1 year later, the serological response is comparable to the standard procedure of two doses of the 1,440 EU vaccine given i.m. and with 100% seroconversion in all three programs.

[Viral hepatitis A: causes of lingering]

The examination covered 756 patients with viral hepatitis A (90 of them were followed up for 1.5 years) who had antigens and antibodies to hepatitis A, B, C, E and D viruses. It was found that: lingering viral hepatitis A may be caused by viral persistence marked by specific antibodies (IgM anti-HAV); lingering hepatitis followed by verification of chronic hepatitis is related to manifestation of previous hepatitis B and C; detection of IgM anti-HAV in patients with exacerbation of chronic hepatitis B, C and D (hepatitis D) evidences for the presence of mix-infection (acute hepatitis A in chronic hepatitis B, C or D).

Molecular epidemiology of an outbreak of hepatitis A in Italy

The relationship of hepatitis A virus (HAV) isolates associated with an outbreak in Genoa, Italy, in 1993 was examined using direct sequencing of amplicons derived by antigen capture PCR (AC/PCR) from faecal samples of the infected persons. Forty samples recovered from 38 primary and two secondary cases were examined. The latter were household contacts of the primary cases. In addition, faecal material of 2 unrelated persons infected simultaneously with hepatitis A in Genoa were tested. The PCR products derived from the P1/P2 junction of the HAV genome were analysed. A 100% nucleotide identity was detected between the viral isolates originating from the primary as well as the secondary cases. The viral isolates recovered from the faecal samples of the two unrelated cases differed from the virus causing the outbreak as well as from each other. These results indicate that a single HAV strain caused the outbreak. The virus might have been transmitted by ingestion of contaminated food or water since all hepatitis A infected employees of the factory had eaten in the same canteen. Definitions of HAV genotypes are based on numerous genetic comparisons of different strains. The sequence comparison of the investigated isolates with published HAV sequences of the P1/P2 genome region revealed that the virus associated with the outbreak belongs to HAV subgenotype IA, whereas the strains recovered from the viral isolates of the unrelated cases belong to subgenotype IB.

Pathogenesis of hepatitis A in orally inoculated owl monkeys (Aotus trivirgatus)

The pathogenesis of hepatitis A virus (HAV) infection was studied in owl monkeys following oral administration of the wild-type HM-175 strain of HAV. Stools were collected daily and blood and pharyngeal swabs twice weekly for viral isolation, and animals were necropsied at various intervals after inoculation. Organs were examined for the presence of virus by isolation in cell culture and for viral antigens by immunofluorescence. Monkeys excreted HAV in the stools for 1-4 days after inoculation, presumably due to the residual unabsorbed inoculum. No virus was found in stools for the next 2-3 days. HAV re-appeared on days 4-7 and then persisted through day 39. Viremia occurred on the 10th day and continued until day 35. Virus was isolated occasionally from throat swabs 1 or 2 weeks after it was detected in stools and blood, and there was no evidence that HAV replicated in the pharyngeal tissues. Animals acquired anti-HAV antibody by the 4th week, and alanine aminotransferase (ALT) was elevated 5-5.5 weeks after inoculation. HAV was isolated from liver 5 days after inoculation; however, viral antigens were first detected in Kupffer cells of the liver at 14 days and in hepatocytes at 21 days. HAV antigen was detected in epithelial cells of the intestinal crypts and in the cells of the lamina propria of the small intestine 3 days postinoculation and thereafter until the 5th week, suggesting that these cells might represent an additional site of HAV replication.

Mimicry of the immunodominant conformation-dependent antigenic site of hepatitis A virus by motifs selected from synthetic peptide libraries

Hepatitis A virus (HAV) is a positive-strand RNA virus with a genome length of approximately 7,480 nucleotides. Although HAV morphogenesis is thought to be similar to that of poliovirus, the prototype picornavirus, the complete characterization of the antigenic structure of this virus remains elusive. All the available evidences, however, support the existence, on HAV virions and empty capsids, of an immunodominant neutralization antigenic site which is conformation dependent and whose structure involves residues of both VP1 and VP3 capsid proteins. This particular feature and the difficulty of obtaining high virus yield in tissue cultures make HAV an ideal target for developing synthetic peptides that simulate the structure of its main antigenic determinant. To this end we utilized, in the present work, the divide-couple-recombine approach to generate a random library composed of millions of different hexapeptides. This vast library was screened with a well-characterized anti-HAV monoclonal antibody. By this strategy we identified a peptide that reacted specifically with monoclonal and polyclonal anti-HAV antibodies and, in mice, induced a specific anti-virus immune response. Furthermore, the peptide could also be used in an enzyme-linked immunosorbent assay for revealing a primary immunoglobulin M immune response in sera of acutely infected human patients. Interestingly, no sequence homology was found between the identified peptide and the HAV capsid proteins VP1 and VP3. Collectively, these data represent an additional important paradigm of a mimotope capable of mimicking an antigenic determinant with unknown tertiary structure.

Efficacy of an inactivated hepatitis A vaccine in pre- and postexposure conditions in marmosets

A two-part challenge study was done in marmoset monkeys to confirm the efficacy of an inactivated hepatitis A vaccine. In part 1 (preexposure), 7 marmosets received a single low dose of vaccine (360 ELISA units [EL.U.]) and were challenged orally with wild type hepatitis A virus (HAV) either 1 or 6 months later. In part 2 (postexposure), 8 marmosets were challenged orally with HAV and then half each were inoculated with a single dose of 360 or 1440 EL.U. of vaccine 2 days later. The suboptimal immune response elicited by the low vaccine dose in the preexposure group was sufficient to induce complete protection against oral challenge with heterologous HAV in all marmosets that had responded serologically. In the postexposure group, the 360-EL.U. dose of vaccine resulted in partial protection against hepatitis A disease, whereas the 1440-EL.U. dose of vaccine elicited complete protection against disease and virus excretion.

Exposure to enteroviruses and hepatitis A virus among divers in environmental waters in France, first biological and serological survey of a controlled cohort

An epidemiological study of hepatitis A and enteroviruses was conducted in a military diving training school, by evaluating the viral contamination of water using an ultrafiltration concentration technique, and assessing seroconversion and the presence of virus in stool specimens obtained from 109 divers and 48 controls. Three of 29 water specimens were positive for enterovirus by cell culture and 9 by molecular hybridization. There was little or no risk of virus infection during the training course (49 h exposure) because there was no significant difference between divers and controls for both viral isolation and seroconversion. However, a higher percentage of coxsackievirus B4 and B5 seropositive divers suggests that these were more exposed during previous water training. No hepatitis A virus (HAV) detection and no seroconversion to HAV was observed. The rate of HAV seropositive subjects was 17% in this 24.5-year-old population.

Synthetic peptides in the determination of hepatitis A virus T-cell epitopes

Computer search for probable T-epitopes of hepatitis A virus capsid proteins was performed using an integrated set of programs. Eight segments of the VP1, VP2, VP3 and VP4 proteins were chosen and synthesised. Five peptides previously examined as probable B-epitopes were used as well. All the peptides were tested for their ability to stimulate proliferation of lymph node T-cells primed with synthetic peptides. Almost all predicted T-epitopes affected the T-cell proliferation. None of the peptides had mitogenic activity. We demonstrated that regions 17-33 and 276-298 of VP1 are possible immunodominant promiscuous sites activating lymphocytes of all mouse haplotypes.

Rapid and efficient purification of hepatitis A virus from cell culture

Hepatitis A virus (HAV) characteristically remains strongly cell-associated when grown in culture, with only small yields in the culture supernatant. Cell factories (6000 cm2) of BS-C-1 cells infected with the cytopathic HM175A.Z strain of HAV for 3, 4 or 7 days were harvested using trypsin to disperse the infected cell monolayer, and cells were collected by low speed centrifugation. More than 70% of the yield of virus and viral antigen can thus be obtained in the packed cell pellet. Packed cell pellets were resuspended in 5 volumes of isotonic buffer and cell membranes lysed by the addition of a non-ionic detergent. After removal of nuclei by centrifugation, ionic detergent was added to the clarified cytoplasmic extract. Under these conditions, HAV particles (virions and empty capsids) are the only particulate material remaining in the sample, and were recovered in a single ultracentrifugation step through discontinuous sucrose/glycerol density gradients. In one day, this method yields viral antigen with minimal cellular contaminants, in a concentrated volume suitable for subsequent biochemical, vaccine or diagnostic uses. The yield of viral antigen over numerous batches varied from 200 to 1600 vaccine-equivalent doses per cell factory, with a titre of up to 1 x 10(10) infectious particles per ml.

Infectivity titration of the fast-replicating and cytopathic hepatitis A virus strain HM175A.2 by an in situ enzyme immunoassay

A simple, rapid and objective infectivity assay based on an in situ enzyme immunoassay (EIA) was developed for the fast-growing and cytopathic cell culture-adapted hepatitis A virus (HAV) strain HM175A.2. Infectivity titration by EIA correlated well with titration by cytopathic effects. The reliability of this assay was demonstrated by close agreement in virus infectivity titers among different assays of the same virus aliquot and between assays of different virus aliquots. HAV infected cell cultures after fixation could be stored for up to 1 week before testing without decline in virus titer.

Studies on mechanism of action of glycyrrhizin against hepatitis A virus replication in vitro

Glycyrrhizin (GL) achieved a concentration-dependent inhibition of the replication of hepatitis A virus (HAV) in PLC/PRF/5 cells. GL has been shown to inhibit an early stage of the HAV replication. GL was not virucidal and had no measurable effect on the adsorption of [3H]uridine-labelled virions to cells. GL inhibited HAV penetration of the plasma membrane as measured by the amount of infective virus no longer neutralizable by specific antibody over time.

[The knowledge base of the Hepaxpert I System: automatic interpretation of Hepatitis A and B serology]

The knowledge base of Hepaxpert-I, a medical expert system for interpretive analysis of hepatitis A and B serologic findings, contains 13 rules for hepatitis A and 106 rules for hepatitis B serology. Formally, the construction of the knowledge base was done by forming a partition of the sets of possible serologic finding patterns--64 for hepatitis A and 4096 for hepatitis B serology--induced by an equivalence relation, divides the elements of the sets into disjoint subsets, the equivalence classes. Each equivalence class is represented as one If-Then rule that assigns to every member of the equivalence class one interpretive text. The partition of the possible finding patterns into equivalence classes and the disposal of one and only one interpretive text for each equivalence class made the creation of a very practical and efficient computer program for the precise interpretation of any finding pattern of serologic tests for hepatitis A and B possible. The complete set of the provided If-Then rules is represented in this paper.

Antibody response to nonstructural proteins of hepatitis A virus following infection

The nonstructural proteins of hepatitis A virus (HAV), produced during active virus replication, are alternative antigens that could be used to differentiate disease from inactivated vaccine-induced antibodies. An assay based on immune precipitation of proteins translated from transcripts of the P2 region of viral cDNA was used to evaluate the development of antibodies after natural infection or vaccination. Antibodies against P2 proteins were found in all sera from clinical cases of hepatitis A following the acute phase. Chimpanzees vaccinated with inactivated or cell-adapted HAV had no detectable antibodies against P2 products, either before or after wild type virus challenge. A serosurvey of sera positive for total anti-HAV (HAVAB, Abbott Laboratories, North Chicago) suggested that some individuals had no detectable antibodies to the P2 antigen by immune precipitation. These results were attributed to the lower sensitivity of the immunoprecipitation assay, since antibodies to capsid proteins, as measured by immunoprecipitation, were also not detected in most of these sera.

Synthesis of immunogenic hepatitis A virus particles by recombinant baculoviruses

Recombinant baculoviruses were constructed which contained the hepatitis A virus (HAV) open reading frame (ORF) under the control of the polyhedrin promoter. Northern blot analysis with an HAV-specific oligonucleotide probe demonstrated a single transcript large enough to include the HAV ORF in Spodoptera frugiperda cells infected with these recombinants. Immunoblots revealed a 220 kDa protein representing the HAV polyprotein. In addition, proteins which co-migrated with HAV capsid proteins, and several proteins of intermediate size were present, consistent with processing intermediates. HAV antigen was present in cells infected with the recombinant baculoviruses when assessed by solid-phase radioimmunoassay. This HAV antigen had a buoyant density in caesium chloride gradients similar to HAV empty capsids, and elicited HAV neutralizing antibodies in mice.

Antigenic and immunogenic properties of recombinant hepatitis A virus 14S and 70S subviral particles

Hepatitis A virus (HAV) has an immunodominant neutralization antigenic site. By using a panel of monoclonal antibodies targeted against the HAV neutralization antigenic site, it was shown that three epitopes within this site are present on 14S subunits (pentamers of the structural unit). In contrast, two other epitopes within this site are formed upon assembly of 14S subunits into capsids. Thus, the epitopes recognized by these two monoclonal antibodies are formed either by a conformational change in the antigenic site or by the juxtaposition of epitope fragments present on different 14S subunits during assembly of 14S into 70S particles. Both 14S and 70S particles elicited HAV-neutralizing antibodies in mice; thus, these particles may be useful for HAV vaccine development.

Immunogenicity and antigenicity of chimeric picornaviruses which express hepatitis A virus (HAV) peptide sequences: evidence for a neutralization domain near the amino terminus of VP1 of HAV

We evaluated the antigenic characteristics of chimeric picornaviruses created by inserting peptide sequences from hepatitis A virus (HAV) capsid proteins into the B-C loop of VP1 of Sabin strain type 1 poliovirus (PV-1). Fifteen viable chimeras were generated. Each retained the ability to be neutralized by polyclonal PV-1 antisera. Two chimeras (H15 and H2) stimulated production of low levels of HAV neutralizing antibodies in immunized rabbits or mice, although in both cases only a small fraction of immunized animals produced this response. The H15 chimera, which contains residues 13-24 of HAV VP1, elicited HAV neutralizing antibodies in three of nine rabbits and at least one of seven immunized mice. These results indicate that a neutralization domain exists in this region of VP1. However, human sera with high titers of antibodies to HAV failed to neutralize or immunoprecipitate this chimera, suggesting the absence of a significant antibody response to this neutralization domain following natural infection. Sera from rabbits immunized with H15 that did not develop HAV neutralizing antibodies contained antibodies reactive with the HAV peptide segment expressed by the H15 virus, indicating substantial differences in the specificities of antibodies elicited by this peptide segment among individual immunized rabbits. The H15 peptide insert was an effective antigen, as indicated by a high level of sensitivity of the H15 chimera to neutralization by a related anti-peptide antibody which was itself devoid of HAV neutralizing activity. One of 16 rabbits immunized with the H2 chimera (residues 101-108 of HAV VP1) developed HAV neutralizing antibodies, confirming both the presence and the highly conformational nature of a neutralization antigenic site involving these residues of HAV.

Natural hosts of hepatitis A virus

The host range for hepatitis A virus (HAV) is limited to man and several species of non-human primates, and involvement of vertebrates other than primates in HAV circulation is unlikely. Spontaneous hepatitis A infection has been reported to occur in captive non-human primates including the great apes (chimpanzee) as well as Old World (cynomolgus, African vervet, stump-tailed) and New World (aotus) monkeys. The presence of anti-HAV antibody in the sera of newly captured monkeys of these species shows that infection may also spread in their natural habitat. HAVs isolated from spontaneously infected monkeys, although antigenically closely related to human HAV, exhibit a significant degree of genomic heterogeneity. There are at least four distinct simian HAVs differing from each other and from all human HAV strains. It is suggested that each virus is native to a given species reflecting evolutionary relationships among HAVs and their hosts in the order of Primates.

Genetic, antigenic and biological differences between strains of hepatitis A virus

Recent studies have documented a considerable degree of genetic divergence among wild-type hepatitis A virus (HAV) strains recovered from different geographical locations. Human HAV strains can be grouped into four genotypes (I, II, III and VII) and unique simian strains belong to three additional genotypes (IV, V and VI). Between each of these genotypes, the nucleotide sequence varies at 15-25% of base positions in the P1 region. Despite this, there is good evidence that most, if not all, human strains of HAV are closely related antigenically. In contrast, although simian strains recovered from Old World monkeys are cross-reactive in immunoassays employing polyclonal antibodies, these strains have significant antigenic differences from human HAV strains. Nonetheless, because biological differences in the host range of these strains apparently preclude significant human infection, this is unlikely to pose a problem in controlling HAV infections with active immunization. Inactivated and attenuated vaccines produced from genotype I human strains (HM175 or CR326) are likely to provide protection against all relevant human HAV strains.

Possible approaches to develop vaccines against hepatitis A

More than a decade ago, successful replication of hepatitis A virus (HAV) in cell culture opened the way to the development of live attenuated and inactivated vaccine candidates. Serial passages of HAV in cell culture led to attenuation as demonstrated by experiments in non-human primates. Several live vaccine candidates obtained through serial passages have been evaluated in volunteers. Significant improvements in the yield of viral antigen from infected cell cultures stimulated the development of killed vaccine candidates. These formalin-inactivated vaccines contain the viral capsid antigens assembled into viral particles. The immunogenic potential of the vaccine candidates depends strongly on the preservation of the configuration of the capsid proteins. Synthetic peptides covering immunogenic sequences of VP1 as well as soluble capsid proteins expressed as fusion proteins in Escherichia coli were therefore only weakly immunogenic when injected at high concentrations in rabbits. On the other hand, tamarin monkeys immunized with a live recombinant vaccinia expressing P1 were protected against virulent challenge. There are, however, considerable drawbacks related to the use of live vaccinia as a carrier virus. Chimeric polio-HAV VP1 viruses have been constructed. These hybrid viruses were not able to induce an immune response, probably because of configurational constraints of poliovirus on the inserted HAV epitopes. More recently, encouraging data on empty virus particles expressed in baculovirus and vaccinia virus systems have been reported.

Laboratory tests and reference reagents employed in studies of inactivated hepatitis A vaccine

Procedures to evaluate inactivated hepatitis A vaccines in volunteers have been examined. Solid-phase immunoassays were standardized with reference preparations and have been tested to measure antibody response to immunization and antigen content of vaccines. Following immunization, there was a good correlation between antibody response, determined with commercial immunoassays, and neutralization titres, as measured by the radioimmunofocus inhibition test. However, at lower titres of neutralizing antibody, the commercial immunoassay often yielded negative results. To improve the sensitivity of the immunoassay, the serum volume was increased. A fourfold increase of test serum resulted in greater sensitivity, increasing from 54 to 94%, while retaining 100% specificity. Further increases in the volume of test serum resulted in a loss of specificity. In a comparison of neutralization tests, similar titres of postvaccination sera were obtained by using the HM175/18f cytopathic strain of hepatitis A virus in a plaque reduction assay or the HM175 parental virus in the radioimmunofocus inhibition test. Use of the cytopathic virus obviates the need for radioactively labelled serum and reduces the time taken to conduct neutralization tests. The current laboratory procedures can meet the needs of large field trials of inactivated hepatitis A vaccines.

Identification and characterization of incomplete hepatitis A virus particles

The range of hepatitis A virus (HAV) particles generated during persistent infection of different cell lines was studied. Buoyant density and sedimentation analyses of cell extracts revealed a uniform profile of particles in all cell lines analysed except for BS-C-1 cells. The virion itself usually represented less than 50% of the total mass of virus antigen. A major portion of the antigen was associated with non-infectious, empty particles, which banded at 1.305 g/ml and 1.20 g/ml CsCl, and sedimented in sucrose gradients at 76S and 59S. Empty HAV particles were similar to those of poliovirus with respect to their physical stability and had the characteristic capsid protein content (VP0, VP1 and VP3). An additional RNA-containing particle, probably the provirion, represented only a minor species characterized by a buoyant density of 1.32 g/ml in CsCl and sedimenting at 130S.

Further evaluation of a live hepatitis A vaccine in marmosets

Live, attenuated F' hepatitis A vaccine virus was studied in vivo in Saguinus labiatus marmosets for possible reversion to virulence, for possible establishment of persistent infection and for its capacity as a parenterally administered vaccine to induce immunity to oral infection. Serial transmission of the virus in S. labiatus, using infectious stool extracts for the second and third passages, produced no evidence of reversion of the F' vaccine virus to virulence. Monitoring for live HAV in stools over a 135-day period post-inoculation of marmosets with the F' vaccine revealed no evidence of persistent infection. Vaccinated animals were also shown to be resistant to infection on challenge by the oral route as well as by the previously demonstrated parenteral route.

Antigenic and genetic variation in cytopathic hepatitis A virus variants arising during persistent infection: evidence for genetic recombination

Variants of hepatitis A virus (pHM175 virus) recovered from persistently infected green monkey kidney (BS-C-1) cells induced a cytopathic effect during serial passage in BS-C-1 or fetal rhesus kidney (FRhK-4) cells. Epitope-specific radioimmunofocus assays showed that this virus comprised two virion populations, one with altered antigenicity including neutralization resistance to monoclonal antibody K24F2, and the other with normal antigenic characteristics. Replication of the antigenic variant was favored over that of virus with the normal antigenic phenotype during persistent infection, while virus with the normal antigenic phenotype was selected during serial passage. Viruses of each type were clonally isolated; both were cytopathic in cell cultures and displayed a rapid replication phenotype when compared with the noncytopathic passage 16 (p16) HM175 virus which was used to establish the original persistent infection. The two cytopathic virus clones contained 31 and 34 nucleotide changes from the sequence of p16 HM175. Both shared a common 5' sequence (bases 30 to 1677), as well as sequence identity in the P2-P3 region (bases 3249 to 5303 and 6462 to 6781) and 3' terminus (bases 7272 to 7478). VP3, VP1, and 3Cpro contained different mutations in the two virus clones, with amino acid substitutions at residues 70 of VP3 and 197 and 276 of VP1 of the antigenic variant. These capsid mutations did not affect virion thermal stability. A comparison of the nearly complete genomic sequences of three clonally isolated cytopathic variants was suggestive of genetic recombination between these viruses during persistent infection and indicated that mutations in both 5' and 3' nontranslated regions and in the nonstructural proteins 2A, 2B, 2C, 3A, and 3Dpol may be related to the cytopathic phenotype.

Detection of IgM against hepatitis A virus using tissue culture derived antigen

Sera from healthy donors and four groups of subjects with acute viral hepatitis were tested for anti-HAV IgM by ELISA with hepatitis A virus antigen grown in tissue culture. The results were compared with those obtained by formalin inactivated HAV from 'HAVAB-M' test kit (Abbott Laboratories, USA). With both preparations of antigens, sera from healthy donors and patients suffering from acute hepatitis B or non-A, non-B did not show anti-HAV IgM antibodies whereas acute phase sera from hepatitis A patients showed strong reactions indicating the presence of anti-HAV IgM antibodies. The results indicate similarity in the specificity of both preparations of HAV against anti-HAV antibodies and encourage the use of tissue culture derived HAV for serological diagnosis of hepatitis A.

Characterization of a hepatitis A virus strain suitable for vaccine production

A novel isolate of hepatitis A virus, obtained from a clinical sample, has been adapted to grow on cultured human diploid cells. Growth and purification parameters have been optimized to obtain conditions suitable for the development of an inactivated vaccine. The entire viral genome was molecularly cloned, and the gene encoding the VP3 capsid protein was expressed in Escherichia coli. The resulting recombinant VP3 was used to obtain rabbit antisera which recognize the denatured protein in purified virion preparations. Nucleotide sequencing data are presented and compared to known sequences of different strains.

The role of secretory immunity in hepatitis A virus infection

Because the role of intestinal immunity remains uncertain in hepatitis A, samples of feces and saliva from infected primates and humans were tested for virus neutralizing activity. Only two of eight owl monkeys infected by the intragastric route developed neutralizing antibody detectable in extracts of feces collected up to 88 days after viral challenge, although serum neutralizing antibody was present in all monkeys by day 33. Similarly, neutralizing antibody was detected in fecal extracts from none of three experimentally infected human volunteers and only 1 of 15 naturally infected humans. The single positive human specimen contained occult blood. Only 2 of 19 saliva samples from naturally infected humans had significant viral neutralizing activity. In contrast, neutralizing antibody to type 2 poliovirus was present in most human fecal or saliva specimens tested. These data suggest that intestinal immunity does not play a significant role in protection against hepatitis A.

Hepatitis A

Known properties of hepatitis A virus are described in this article. HAV is a small non-enveloped picornavirus, grouped in the Enterovirus family, with unique biological features. The genome structure resembles that of other picornaviruses. Replication in cell cultures takes much longer than that of other picornaviruses and the yield is much lower. HAV is extremely heat- and pH-stable. Variants may induce cytopathogenic effects in vitro. Normally, however, the virus is non-cytopathogenic. The elimination of virus in vivo is assumed to be caused by action of HAV antigen specific CD8+ lymphocytes. In industrialized countries there is a declining incidence of reported hepatitis A cases, and the prevalence of antibodies in younger populations is low. Vaccines have been developed and in studies using human volunteers, good immunogenicity has been demonstrated. In the very near future a cell cultured derived, highly purified, inactivated vaccine will be available.

Inhibition of hepatitis A virus replication in vitro by antiviral compounds

Forty antiviral compounds were screened for inhibitory effect on hepatitis A virus (HAV) antigen expression in the human hepatoma cell line PLC/PRF/5. Ribavirin, amantadine, glycyrrhizin, and pyrazofurin were selected in this screening test and were studied further. The selectivity indices of these four compounds, calculated as the ratio of 50% cytotoxic dose (determined by the trypan blue exclusion and by inhibition of [3H] leucine incorporation) to the 50% effective dose (determined by the viral antigen expression), were 4.6 and 3.0 with ribavirin, 5.3 and 5.9 with amantadine, 15.2 and 16.9 with glycyrrhizin, and 45.4 and 74.6 with pyrazofurin. All four compounds resulted in concentration-dependent reductions of HAV antigen expression and HAV infectivity. Ribavirin, amantadine, pyrazofurin, and glycyrrhizin emerged, from the present study, as promising candidates for chemotherapy of acute hepatitis A.

Recovery of hepatitis A virus from a water supply responsible for a common source outbreak of hepatitis A

An outbreak of hepatitis A occurred in a north Georgia trailer park served by a private well. Of 18 residents who were serosusceptible to hepatitis A virus (HAV), 16 (89%) developed hepatitis A. Well water samples were collected 3 months after illness onset in the index case and 28 days after illness onset in the last trailer park resident. Hepatitis A virus antigen (HAVAg) was detected in the samples by enzyme immunoassay from three of the five cell lines following two 30-day passages and from a fourth cell line following a third passage of 21 days.

Monoclonal antibodies against an immunodominant and neutralizing epitope on hepatitis A virus antigen

Two monoclonal antibodies (813 and 10.09) were raised against hepatitis A virus (HAV). They recognize an immunodominant epitope and a neutralizing site on HAV.

Structure of the hepatitis A virion: identification of potential surface-exposed regions

Iodination of highly purified hepatitis A (HAV) virus results in the selective labeling of two viral polypeptides, which are identified as the the VP 1 and VP 2 capsid polypeptides. Based upon the kinetics of labeling, the exposed region of VP 1 appears to be more accessible to iodination, although the ultimate proportion of label present within VP 1 and VP 2 is approximately equal. By utilizing iodinated whole virions, isolated VP 1, VP 2, and the tryptic digest derived from VP 1 and VP 2, binding by heterologous anti-160 S antibody indicated that a significant portion of the antibodies was directed against an epitope on VP 2 that was not affected by denaturation. Identification of the regions exposed for iodination on these two polypeptides was accomplished by tryptic digestion of the isolated polypeptides followed by characterization of the iodinated tryptic peptide by gel filtration and reverse-phase chromatography. The results indicate that tyrosine 100 on VP 2 and a large tryptic peptide composed of amino acids 222 through 260 on VP 1 which contains four tyrosine residues are two regions that are surface-exposed on these molecules.