The polypeptides of hepatitis A virus

Molecular biology of hepatitis A virus: significance of various substitutions in the hepatitis A virus genome

Hepatitis A virus (HAV) is the sole member of the hepatogenus of Picorna viridae. This virus can now be propagated in cell culture and in primates. Molecular biological studies of HAV have disclosed its genomic structure and the functional significance of the viral proteins to some extent. Hepatitis A virus has a positive-stranded RNA of approximately 7.5 kb that encodes a large polyprotein. Translation of the protein is influenced by the function of the internal ribosomal entry site in the 5' non-translating region. It is generally agreed that the polyprotein is processed to four structural and seven non-structural proteins by the proteinase encoded in the 3C region. Replication efficiency seems to be controlled by amino acid substitutions in the 2B and 2C regions. The virulence of HAV in primates may be determined by substitutions in the 2C region. Although the severity of hepatitis A was thought to be determined by immunological reactions of the host to the virus, the potential virulence of the variant viruses themselves may need further examination. Recent progress in polymerase chain reaction technology has made possible an analysis of the HAV sequence in clinical specimens; such analysis is of importance in the disclosure of differences in HAV subspecies in different clinical conditions.

Altered hepatitis A VP1 protein resulting from cell culture propagation of virus

The published sequence of hepatitis A virus (HAV), strain HAS-15, after 20-30 cell culture passages contains an 18 nucleotide deletion (Ovchinnikov et al., 1985) within the VP1 genome region. This results in a significant amino acid difference of the VP1 protein when this strain of HAV is compared with other published HAV sequences. Comparison of the polyacrylamide gel electrophoretic migration of HAS-15 HAV and two other strains of HAV revealed that the HAS-15 VP1 molecule migrated faster than the VP1 molecule of the other two strains. Enzymatic amplification of viral RNA derived from the original stool suspension and cell culture adapted HAS-15 using the polymerase chain reaction followed by hybridization analyses with selected synthetic oligonucleotide probes revealed that the original wild type virus did not contain the deletion. These results confirm that cell culture adapted HAS-15 contains an eighteen nucleotide deletion which apparently was selected during cell culture adaptation.

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.

The entire nucleotide sequence of the genome of human hepatitis A virus (isolate MBB)

Hepatitis A virus (HAV) is an important human pathogen causing hepatitis, with high incidence in developed as well as in developing countries. No vaccines are available. In order to determine the primary structure of the HAV genome, we have prepared cDNAs from viral RNA and cloned these into plasmid pBR322. These clones were used to determine the entire nucleotide sequence of the HAV RNA by rapid sequencing methods. We have compared this sequence of 7470 bases to known partial sequences, and one complete sequence of HAV RNA which were obtained recently from different strains of HAV. It is hoped that a comparison of sequence data from different isolates will help in the elucidation of the unusual growth pattern of HAV. In addition, it might provide helpful information about the immunological determinants that elicit the antibody response to infection.

Detection of hepatitis A virus and antibody by solid-phase radioimmunoassay and enzyme-linked immunosorbent assay with monoclonal antibodies

Monoclonal antibodies (K3-2F2 and K3-4C8) raised against hepatitis A virus were used to develop a solid-phase radioimmunoassay and enzyme-linked immunosorbent assay for the detection of hepatitis A virus and antibody. Assays with this pair of monoclonal antibodies were compared in parallel with similarly constructed solid-phase radioimmunoassays and enzyme-linked immunosorbent assays in which human polyclonal serum was used. The monoclonal antibody assay proved to be more sensitive for the detection of hepatitis A virus from fecal specimens as well as for anti-hepatitis A virus immunoglobulin G (IgG) and IgM in sera.

Primary structure and gene organization of human hepatitis A virus

The RNA genome of human hepatitis A virus (HAV) was molecularly cloned. Recombinant DNA clones representing the entire HAV RNA were used to determine the primary structure of the viral genome. The length of the viral genome is 7478 nucleotides. An open reading frame starting at nucleotide 734 and terminating at nucleotide 7415 encodes a polyprotein of Mr 251,940. Comparison of the HAV nucleotide sequence with that of other picornaviruses has failed to reveal detectable areas of homology. However, a computer analysis of the putative amino acid sequence of HAV and poliovirus demonstrated the existence of short areas of homology in virion protein 3 (VP3) and throughout the carboxyl-terminal portion of the polyproteins. In addition, extensive protein structural homologies with poliovirus were detected.

Monoclonal antibodies against hepatitis A virus

Three monoclonal antibodies (K2-4F2, K3-2F2, and K3-4C8) of the immunoglobulin G2a class were raised against hepatitis A virus. The specificity of these antibodies was confirmed by immune electron microscopy, solid-phase radioimmunoassay, and in vitro neutralization in cell culture. Binding studies suggested that they all recognize closely related antigenic determinants. These monoclonal antibodies should prove to be of great value as diagnostic and research reagents.

Hepatitis A virus: virologic, clinical, and epidemiologic studies

The last decade has borne witness to accelerated expansion of our understanding of hepatitis A virus. The agent of type A hepatitis is an RNA virus with a mean diameter of 27 nm. and biochemical-biophysical properties of an enterovirus. A variety of sensitive specific serologic techniques have been developed with which to identify hepatitis A virus and antibody, and both chimpanzees and marmosets have been studied extensively as experimental animal models. As a result of these studies, in vitro cultivation of hepatitis A virus has finally been accomplished, and a commercial radioimmunoassay for IgM antibody to hepatitis A virus has been developed for the rapid diagnosis of hepatitis A virus infection during acute illness. Clinically the illness caused by hepatitis A virus is relatively mild, often subclinical, and of limited duration and does not progress to chronic liver disease. This relative clinical benignity is reflected, according to preliminary histologic observations, in the sparing of the centrozonal area of the liver lobule. Rarely, however, hepatitis A virus can cause fulminant hepatitis. Type A hepatitis is transmitted almost exclusively by the fecal-oral route, and its spread is enhanced by epidemiologic settings favoring dissemination of enteric infections. Hepatitis A virus does not contribute to transfusion associated or other types of percutaneously transmitted hepatitis. Exposure to the virus increases as a function of age and decreasing socioeconomic class, but the incidence of hepatitis A virus infection in urbanized societies is decreasing. There is no evidence for the existence of chronic hepatitis A virus carriage; natural perpetuation of hepatitis A virus in urban communities appears to depend on a reservoir of nonepidemic, clinically inapparent cases. Until a vaccine, now being developed, becomes available, prevention of hepatitis A virus infection will continue to depend on maintenance of high standards of environmental and personal hygiene and on timely administration of immune serum globulin. Such prophylaxis may confer long lasting passive-active immunity but more frequently prevents infection entirely.

Cloning of hepatitis A virus genome

Hepatitis A virus (HAV) was highly purified from faeces. The genomic RNA was transcribed to cDNA and this DNA was then cloned into plasmid pBR 322 at the Pst I site, and clones were selected in presence of tetracycline. Most clones contained inserts which hybridized to HAV-specific RNA isolated from HAV-infected cell cultures derived from a human hepatocellular carcinoma. Two clones expressed low amounts of viral antigens.

Characterization and classification of virus particles associated with hepatitis A. III. Structural proteins

Hepatitis A virus was purified from fecal samples collected at various times in the incubation period of patients with naturally acquired hepatitis A. The proteins of particles banding at around 1.34 g/ml in CsCl and sedimenting at about 160S were radioiodinated in vitro and separated by electrophoresis on polyacrylamide gels in the presence of 0.1% sodium dodecyl sulfate and 8 M urea. Under these conditions, the capsid proteins resolved into four polypeptides with molecular weights of approximately 31,000, 24,500, 21,000, and 9,000, respectively. A fifth protein of about 40,000 daltons in size and assumed to be equivalent to the precursor polypeptide VP0 of the picornaviruses was present in particles sedimenting at only 150 to 155S and banding at around 1.33 g/ml in CsCl. The physicochemical characteristics of these particles are consistent with those of the provirion structures of picornaviruses. In several of the fecal samples, these particles represented a considerable fraction of all particles present. The significance of this finding with respect to the antigenicity of hepatitis A antigen extracted from stool specimens is discussed.

Propagation of human hepatitis A virus in African green monkey kidney cell culture: primary isolation and serial passage

Human hepatitis A virus (HAV) was propagated in primary African Green Monkey (Cercopithecus aethiops) kidney (AGMK) cell cultures. Three strains of HAV were used: MS-1, SD-11, and HM-175. Cells were inoculated with marmoset-passaged material or human clinical specimens and were stained by direct immunofluorescence to establish the identity of the virus. Both clinical samples and marmoset-passaged material produced immunofluorescence. HAV antigen was found scattered throughout the cytoplasm of inoculated cultures. The HM-175 strain produced the most intense immunofluorescence. This strain of HAV had been serially passaged in cell culture seven times. Blocking experiments with paired human sera from naturally acquired HAV infections and hyperimmune chimpanzee serum from an experimentally infected animal established that the immunofluorescence was specific. The viral antigen was found to be exclusively intracellular. The interval to maximum HAV antigen expression was decreased by serial passage. The HAV strain described herein, which was recovered directly from the stool specimen of a patient with HAV in primary AGMK cell culture, may prove useful as a source of antigen for serological tests and as a candidate vaccine strain.

Evidence that the genome of hepatitis A virus consists of single-stranded RNA

Nucleic acid was extracted from purified hepatitis A virus, radiolabeled with 125I, and shown to consist of single-stranded RNA which sediments at 35S and contains sequences of polyadenylic acid. These findings are consistent with hepatitis A virus being a member of the genus Enterovirus within the family Picornaviridae.

Restricted replication of human hepatitis A virus in cell culture: intracellular biochemical studies

When hepatitis A virus was inoculated into Vero cells, virus-specified protein and RNA synthesis was detected. Production of viral protein was detected by electrophoretic analysis in polyacrylamide gels by using a double-label coelectrophoresis and subtraction method which eliminated the contribution of host protein components from the profiles of virus-infected cytoplasm. Eleven virus-specified proteins were detected in the net electrophoretic profiles of hepatitis A virus-infected cells. The molecular weights of these proteins were very similar to those detected in cells infected with poliovirus type 1. Virus-specified protein synthesis could be detected at 3 to 6 h and continued for at least 48 h postinfection, but no significant effect on host-cell macromolecular synthesis was observed. Limited viral RNA replication occurred between 2 and 6 h postinfection. The genomic RNA of hepatitis A virus was extracted and shown to be capable of infecting cells and inducing the same set of proteins as intact virus, indicating that the RNA genome is positive stranded. Progeny virus was never detected in the supernatant fluids of infected cell cultures, and the cells showed no observable cytopathology, even though hepatitis A virus-specific proteins and antigens were being produced. The nature of the defect in the replicative cycle of hepatitis A virus in this system remains unknown.

Hepatitis A virus infection: pathogenesis and serodiagnosis of acute disease

The early development of immune electron microscopic (IEM) methods for the detection of HAV in acute-phase stool suspensions and antibody to HAV (anti-HAV) in serum made it possible to serologically identify cases of hepatitis A using paired acute and convalescent phase sera. Introduction of less cumbersome and time-consuming serologic test methods, including complement fixation (CF) and immune adherence hemagglutination (IAHA), made it feasible to rapidly assay larger numbers of specimens for HAV or anti-HAV. Subsequent development of sensitive immunofluorescence (IF) assays, solid-phase radioimmunoassays (RIA), and enzyme immunoassays (EIA) for HAV and anti-HAV heralded intensive laboratory studies of the biophysical and biochemical properties of the virus as well as efforts to define the pathogenesis and clinical course of disease. Results of the latter studies showed that the bulk of HAV was usually excreted in stool before the onset of clinical symptoms. Other serologic studies demonstrated that all acutely ill patients had circulating anti-HAV IgM, while all convalescent patients were positive for anti-HAV IgG. The development of sensitive serologic tests (RIA and EIA) that could differentiate between anti-HAV IgM and IgG made it possible to serodiagnose an acute case of hepatitis A using a single-phase serum specimen.

Iodination of hepatitis A virus reveals a fourth structural polypeptide

Hepatitis A virus present in the feces of two patients with naturally acquired hepatitis A was purified, radiolabeled with 125I, and analyzed by discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition to the three structural polypeptides previously reported, a fourth polypeptide with a molecular weight of 14,000 was detected and shown to be a component of hepatitis A virus by immune precipitation techniques. Intact virions were also shown to sediment at 160S on sucrose gradients. These findings are consistent with hepatitis A virus being an enterovirus within the family Picornaviridae.

Coproantibodies in hepatitis A: detection by enzyme-linked immunosorbent assay and immune electron microscopy

A collection of 104-fecal specimens from 45 patients with hepatitis A, 14 patients with hepatitis B, 10 patients with non-A, non-B hepatitis, 6 patients with diseases other than hepatitis, and 18 healthy adults were studied for the presence of secretory immunoglobulin A and immunoglobulin M to hepatitis A virus by solid-phase enzyme-linked immunosorbent assay and immune electron microsopy. Specific fecal antibody was found only in patients with hepatitis A. Of 54 specimens from patients with hepatitis A, only 10 (18.5%) possessed detectable levels of fecal antibody, and each of these was collected within 10 days from the onset of dark urine. All 10 fecal specimens contained hepatitis A-specific secretory immunoglobulin A, and 4 were also positive for hepatitis A-specific immunoblobulin M. Four of the 10 antibody-positive specimens also contained hepatitis A virus particles which could be shown by immune electron microscopy to be coated with specific secretory immunoglobulin A. Since specific fecal antibody was not detected in all the patients with hepatitis A that were studied, it would appear to have limited diagnostic value, although its detection is evidence of recent infection.

Purification of hepatitis A virus by affinity chromatography

Hepatitis A virus was purified from faeces by immunoaffinity chromatography.

Developments in viral hepatitis

Viral hepatitis is a major public health problem occurring endemically in all parts of the world. The general term viral hepatitis refers to infections caused by hepatitis virus type A, type B and a more recently identified infection referred to as "non-A: non-B" hepatitis. These clinically and pathologically similar forms of hepatitis have been studied intensively following the discovery of a specific antigen, Australia antigen, one of the markers of infection with hepatitis B virus.