Molecular basis of virulence and growth of hepatitis A virus in cell culture

The ability of engineering variants of hepatitis A virus (strain HM175) to replicate in cell culture or to cause disease in marmosets was evaluated. Virus variants were encoded by chimeric genomes constructed from infectious cDNA clones of two viruses (wild type and cell-culture-adapted) which differed in their ability to grow in vitro and to cause acute hepatitis in marmosets. Transfection and infectivity assays indicated that virus growth in vitro could be enhanced by subcloning the cell substrate prior to infection or by introducing multiple combinations of two or more mutations into the wild type genome. Various chimeric viruses induced liver enzyme elevations in marmosets, indicating that attenuation of virulence also required multiple mutations.

Inactivated hepatitis A vaccine: active and passive immunoprophylaxis in chimpanzees

Studies of active and passive immunoprophylaxis were carried out in chimpanzees to determine whether a candidate hepatitis A virus (HAV) vaccine could stimulate antibody to HAV (anti-HAV) that was qualitatively similar to anti-HAV stimulated by natural infection. Normal immune globulin (Ig) was prepared from plasma obtained from human volunteers before and after vaccination with the HAV vaccine, and these preparations or commercially prepared Ig were administered to chimpanzees. Protective efficacy was compared to that obtained after vaccination of chimpanzees. As expected, pre-vaccination Ig did not protect chimpanzees against challenge with virulent hepatitis A. In contrast, chimpanzees were protected against hepatitis A by Ig prepared from volunteers who had received hepatitis A vaccine. The protection was qualitatively similar to that afforded by commercial normal Ig containing convalescent anti-HAV. The minimum protective dose of passively acquired anti-HAV was approximately the minimum dose detectable by serological means. This information will be useful in calculating minimum acceptable titres of anti-HAV in normal Ig. Whereas administration of Ig protected chimpanzees against hepatitis A pathology, it did not protect them from infection with HAV. Thus, these chimpanzees were protected by classical passive-active immunoprophylaxis. In contrast, chimpanzees actively immunized with HAV vaccine were apparently protected against both hepatitis A pathology and HAV infection. The mechanism of this complete protection is unknown but may simply represent the higher titre of anti-HAV in the vaccinated chimpanzees, compared to the passively protected animals.

Mutations responsible for adaptation of hepatitis A virus to efficient growth in cell culture

Chimeric genomes of hepatitis A virus strain HM-175 were constructed from cDNA clones of the wild-type virus and its cell culture-adapted variant. RNA transcribed in vitro from each construct was assayed for infectivity by transfection of cultured cells. RNA transcribed from the wild-type cDNA clone was minimally infectious and produced virus that grew inefficiently in vitro, whereas that transcribed from certain chimeric genomes consistently produced virus that grew efficiently in cultured cells. Mutations in the P2 region were found to be necessary for efficient virus growth in vitro, while mutations in the 5' noncoding region imparted a conditional enhancement of growth in vitro.

A long-term study of hepatitis C virus replication in non-A, non-B hepatitis

BACKGROUND

Although antibodies to the hepatitis C virus (HCV) are known to be associated with non-A, non-B hepatitis, little is known about the pattern of HCV replication, its relation to antibody levels, and the clinical course of non-A, non-B hepatitis.

METHODS

We measured HCV RNA in serial serum samples from five patients with post-transfusion non-A, non-B hepatitis who were followed for 10 to 14 years after transfusion. We also studied four chimpanzees that were experimentally infected with serum from four of these patients. Serum HCV RNA was detected by a "nested" polymerase-chain-reaction (PCR) assay that used two sets of primers derived from the third (NS3) and fourth (NS4) non-structural gene regions of the HCV genome.

RESULTS

HCV sequences were detected by PCR in only two of the five patients and two of the four chimpanzees with the set of primers corresponding to the NS3 region, but in all five patients (and in all four chimpanzees) with the primers from the NS4 region. Serum HCV RNA was first detected within three weeks of transfusion in all five patients and within one week in three patients. The viremia lasted less than 4 months in the patient (and two chimpanzees) with acute, self-limited hepatitis, whereas it persisted for 10 to 14 years in the four patients (and for 1 and 3 years in two chimpanzees) with chronic non-A, non-B hepatitis. Antibodies to HCV were first detected at week 12 to 14; they disappeared after nine years in the patient with self-limited disease and became borderline after five years in one of the patients with chronic disease.

CONCLUSIONS

During the early phase of primary HCV infection, there is a period of several months of sero-negativity during which HCV RNA is the only diagnostic marker of infection. The disappearance of HCV RNA from serum appears to correlate with the resolution of non-A, non-B hepatitis, whereas viremia persists in patients whose disease progresses to chronic hepatitis. In contrast, antibody levels do not necessarily remain elevated in patients with chronic disease.

Simian hepatitis A virus (HAV) strain AGM-27: comparison of genome structure and growth in cell culture with other HAV strains

Fragments of cDNA representing greater than 99% of the entire genome of wild-type hepatitis A virus (HAV) strain AGM-27, isolated from an African green monkey, were obtained by the polymerase chain reaction and sequenced. Comparison with other HAV isolates revealed differences in the predicted amino acid sequence in functionally critical parts of the genome. Comparison of the biological properties of AGM-27 with those of human wild-type and cell culture-adapted HM-175 strains revealed that AGM-27 grew in cell culture significantly better than did wild-type HM-175, but not as well as cell culture-adapted HM-175. AGM-27 and cell culture-adapted HM-175 were distinguishable by their differential growth in CV-1, FRhK-4 and primary AGMK cells.

Nucleotide sequence and mutation rate of the H strain of hepatitis C virus

Patient H is an American patient who was infected with hepatitis C virus (HCV) in 1977. The patient became chronically infected and has remained so for the past 13 years. In this study, we compared the nucleotide and predicted amino acid sequences of the HCV genome obtained from plasma collected in 1977 with that collected in 1990. We find that the two HCV isolates differ at 123 of the 4923 (2.50%) nucleotides sequenced. We estimate that the mutation rate of the H strain of HCV is approximately 1.92 x 10(-3) base substitutions per genome site per year. The nucleotide changes were exclusively base substitutions and were unevenly distributed throughout the genome. A relatively high rate of change was observed in the region of the HCV genome that corresponds to the non-structural protein 1 gene region of flaviviruses, where 44 of 960 (4.6%) nucleotides were different. Within this region there was a 39-nucleotide domain in which 28.2% of the nucleotides differed between the two isolates. In contrast, relatively few nucleotide substitutions were observed in the 5' noncoding region, where only 2 of 276 (0.7%) nucleotides were different. Our results suggest that the mutation rate of the HCV genome is similar to that of other RNA viruses and that genes appear to be evolving at different rates within the virus genome.

Attempts to transmit hepatitis B virus to chimpanzees by arthropods

Bedbugs (Cimex lectularius L.) were fed on an infective blood-hepatitis B virus (HBV) mixture. Further bedbugs and tampan ticks (Ornithodoros moubata [Murray]) were fed on HBV-carrier chimpanzees. After a 10-13 day interval for oviposition, tests done on samples of individual arthropods showed that 53-85% of the bugs were HBsAg-positive and none HBeAg-positive, while 100% of the ticks were HBsAg-positive and 88% HBeAg-positive. The remaining arthropods were fed on 3 susceptible chimpanzees, which had failed to develop HBV infection after 11 months, indicating no transmission had occurred. Subsequently the presence of viable virus in the original infective meals was confirmed by inoculation of the relevant donor sera directly into the 3 still susceptible chimpanzees. HBV infections quickly followed in each animal. It is concluded that, while mechanical transmission of HBV is most unlikely after a 10-13-day interval between feedings in bedbugs and tampans, it is still possible that mechanical transmission between humans might occur during interrupted feeds.

Biological and molecular comparisons of human (HM-175) and simian (AGM-27) hepatitis A viruses

Comparisons of HM-175, the prototype human strain of hepatitis A virus, and AGM-27, a simian isolate, indicate that the two HAV viruses differ substantially in sequence and in biological characteristics. The extent of the differences suggests that hepatitis A viruses have a greater potential for diversity than previously assumed.

The nature of genetic variation among viruses

Genetic variation among viruses may seem unimportant and academic--related only to pedagogical classification of things--but accurate determination of genetic relationships can have important implications, from characterizing the molecular basis of attenuation of viral vaccines to furthering knowledge about origins of viruses and even of life itself. It can even help to establish priority in the discovery of viruses when properly applied. The purpose of this brief review is to demonstrate how viruses change and what implications these changes can have on the delicate balance between the viral parasite and its host. Examples will be drawn from the hepatitis viruses when possible.

Evidence against a requisite role for defective virus in the establishment of persistent hepadnavirus infections

The factors involved in the establishment of persistent hepadnavirus infection are poorly understood. Recent findings demonstrate that the sequence of the genome of hepatitis B virus (HBV) is variable in infected individuals and that, in some cases, virus mutants predominate. Our objectives in the present study were to analyze the variability of woodchuck hepatitis virus (WHV) genomes in an infected animal and to determine whether sequence heterogeneity played a critical role in the ability of WHV to induce chronic infection. We cloned and determined the complete nucleotide sequence of three supercoiled genomes from an animal that became infected after inoculation with a standardized WHV serum pool (i.e., the WHV7 virus pool). We found that there were four nucleotide substitutions among the three genome sequences as well as a 73-nucleotide deletion in one of the recombinants. DNA transfection experiments revealed that only one of the three recombinants was capable of independent replication. These data suggest that a significant proportion of replicative templates in woodchucks that are infected with WHV are defective virus genomes. Next, we compared the outcome of acute infection after inoculation with a serum pool containing a uniform population of replication competent virus (i.e., the WHV7R pool) with a serum pool composed of WHV genomes of variable sequence. The WHV7R serum pool originated from a woodchuck that became a chronic carrier after in vivo transfection of the liver with the infectious WHV7 recombinant. Neonatal woodchucks were inoculated with 5 x 10(6) WHV genome equivalents of either the WHV7 pool or the WHV7R pool. All animals in the study became acutely infected with WHV. Of the animals infected with the WHV7 serum pool, 65% became chronic carriers, while 80% of the animals infected with the WHV7R serum pool developed chronic infection. Thus, infection of woodchucks with a serum pool containing defective virus resulted in a rate of chronic WHV infection that was similar to, or even lower than, a rate from a pool containing only wild-type virus. This suggests that the presence of defective virus in the inoculum is not a prerequisite for the establishment of persistent hepadnavirus infections.

19S and 7-8S forms of IgM antibody to hepatitis B core antigen in acute icteric hepatitis superimposed on hepatitis B surface antigen carriage

The 19S and 7-8S forms of IgM antibody to hepatitis B core antigen (IgM anti-HBc) were separated by rate-zonal centrifugation from the serum of 20 Greek hepatitis B surface antigen (HBsAg) carriers with a superimposed acute icteric hepatitis positive for IgM anti-HBc by a radioimmunoassay. Serological markers of hepatitis A virus (HAV), hepatitis B virus (HBV) and hepatitis D virus (HDV) infections were detected with radioimmunoassays and serum HBV DNA was detected with molecular hybridization techniques. Eighteen of the 20 carriers showed a predominance of one or the other form of IgM anti-HBc. Low molecular weight (7-8S) IgM anti-HBc was observed more frequently in HDV superinfection (5/9) and was related to a low mortality (1/9). In contrast, 19S IgM anti-HBc was observed more frequently in reactivation of chronic hepatitis B (6/9) and was related to a high mortality (5/9). These preliminary data show that in HBsAg carriers with a superimposed acute icteric hepatitis, predominance of 19S IgM anti-HBc is frequently associated with a severe clinical course; the opposite is true for predominance of 7-8S IgM anti-HBc.

Interrelationship of blood transfusion, non-A, non-B hepatitis and hepatocellular carcinoma: analysis by detection of antibody to hepatitis C virus

To clarify the relationship between hepatitis C virus infection and the development of hepatocellular carcinoma as sequelae of non-A, non-B posttransfusion hepatitis, 231 patients with chronic non-A, non-B hepatitis (96 with chronic hepatitis, 81 with cirrhosis and 54 with hepatocellular carcinoma) were analyzed for antibody to hepatitis C virus and were compared with 125 patients with chronic hepatitis B (50 with chronic hepatitis, 46 with cirrhosis and 29 with hepatocellular carcinoma). Antibody to hepatitis C virus was detected in 89.6%, 86.4% and 94.4% of patients with non-A, non-B hepatitis-related chronic hepatitis, cirrhosis and hepatocellular carcinoma, respectively, compared with 6%, 17.4% and 34.5% with similar diseases related to hepatitis B. A history of transfusion was documented in 52%, 33% and 42% of anti-hepatitis C virus-positive cases of chronic hepatitis, cirrhosis and hepatocellular carcinoma. The mean intervals between the date of transfusion and the date of diagnosis of anti-hepatitis C virus-positive chronic hepatitis, cirrhosis and hepatocellular carcinoma were 10, 21.2 and 29 yr, respectively. In 21 patients with transfusion-associated hepatocellular carcinoma, anti-hepatitis C virus was present in each serial sample available for testing, including samples obtained up to 14 yr before the diagnosis of hepatocellular carcinoma. These data suggest the slow, sequential progression from acute hepatitis C virus-related non-A, non-B hepatitis through chronic hepatitis and cirrhosis to hepatocellular carcinoma and support a causal association between hepatitis C virus and hepatocellular carcinoma.

Detection of hepatitis B virus DNA in serum by polymerase chain reaction. Application for clinical diagnosis

Standard methods of virus DNA detection using the polymerase chain reaction can be time consuming and can involve multiple steps in which contamination with exogenous DNA can occur. Therefore, we developed a simplified method for detecting hepatitis B virus DNA in serum. The main advantages of this method are that it can be performed rapidly, consists of only several steps, and has a false positive rate of less than 0.1% in our laboratory. In testing serial samples from five chimpanzees experimentally infected with hepatitis B virus, we found that hepatitis B virus DNA was detected 2-3 weeks before the appearance of hepatitis B surface antigen, and it continued to be detectable 1-3 weeks after the production of antibody to hepatitis B surface antigen. In testing serum from 84 human patients, we found hepatitis B virus DNA in all patients who had hepatitis B surface antigen and hepatitis B e antigen in serum and in 64% of the patients with hepatitis B surface antigen with antibody to hepatitis B e antigen in serum. Also, 3 out of 11 patients who were chronic hepatitis B carriers and who subsequently lost hepatitis B surface antigen were found to test positive for hepatitis B virus in serum. In contrast, all patients who lost hepatitis B surface antigen after acute hepatitis B virus infection or those classified as having non-A, non-B hepatitis tested negative for hepatitis B virus DNA. Thus, the modified PCR technique is a sensitive and rapid method for detecting hepatitis B virus DNA-containing virions in serum.

Hepatitis B virus DNA detection and comparison with hepatitis B surface antigen

Hepatitis B surface antigen (HBsAg) has been used for the detection of hepatitis B virus (HBV). Recently, HBV detection using the polymerase chain reaction (PCR) has been shown to be a direct measure of complete virions and to be potentially a very sensitive method. Therefore, we attempted to analyze the relationship between HBsAg detection and HBV DNA assay by PCR. We tested HBV DNA by a modification of the PCR technique in serial sera from five chimpanzees experimentally infected with HBV and 29 human sera. Our new method of PCR analysis is as sensitive as former methods but is more simple and rapid than existing procedures. In chimpanzee studies, HBV DNA was detected 2-3 weeks before the appearance of HBsAg, and continued to be detectable 2 weeks after the production of antibody to HBsAg. Also, 3 of 11 chronic hepatitis B patients who lost HBsAg were positive for HBV DNA in serum, while all of patients who recovered from acute viral infection were negative for HBV DNA in serum. These results indicate that HBV DNA detection by PCR analysis is the most sensitive method currently available to detect the presence of complete virions in serum.

Early events in hepatitis C virus infection of chimpanzees

The cytoplasmic antigen and ultrastructural changes we described previously for chimpanzees (Pan troglodytes) infected with hepatitis C virus (HCV) or with hepatitis D virus have recently been shown to be indirect measures of viral replication and appear to represent a host response to the expression or action of interferon. The time of appearance of these changes in hepatocytes during HCV infection, when compared with similar changes in hepatitis D virus infection, suggests a very early replicative phase for HCV. To investigate the early events in HCV infection, we infected two chimpanzees with HCV and obtained blood and liver biopsy samples from them daily during the first 10 days of infection. The early stage of infection with regard to HCV replication, antigen expression, and ultrastructural changes was similar in both chimpanzees. When tested by cDNA/polymerase chain reaction, HCV sequences became detectable in the serum as early as 3 days after inoculation and remained positive through the peak of aminotransferase elevations. In one chimpanzee the peak of virus production appeared to be 7 weeks after inoculation, which was coincident with rising enzyme values. The cytoplasmic antigen, detected by immunofluorescence, and ultrastructural changes, detected by electron microscopy, became positive in hepatocytes 3 and 6 days, respectively, after HCV sequences were first detected in serum. Circulating anti-HCV appeared 13 weeks and 32 weeks after inoculation, respectively, in the chimpanzees. These data indicate a very early replicative phase for HCV and a potentially long period of infectivity before the appearance of anti-HCV.

Evaluation in chimpanzees of vaccinia virus recombinants that express the surface glycoproteins of human respiratory syncytial virus

The immunogenicity and protective efficacy of recombinant vaccinia viruses that express the two major protective antigens of human respiratory syncytial virus (RSV), the F and G glycoproteins, were evaluated in chimpanzees. In previous studies in rodents and monkeys the F and G proteins expressed by the same recombinants were highly immunogenic and induced high levels of resistance to RSV replication following subsequent challenge. In contrast, in chimpanzees, a single intradermal immunization induced only moderate levels of F and G-specific serum antibodies as measured by an enzyme-linked immunosorbent assay, and these antibodies did not efficiently neutralize RSV infectivity in vitro. This poor antibody response in chimpanzees to the F and G glycoproteins occurred despite efficient replication of the vaccinia virus vector as evidenced by lesion size and serum antibody response to vaccinia virus. Upon intranasal RSV challenge, it was observed that prior immunization with the F and G recombinants effected only a marginal reduction in the magnitude and duration of RSV shedding from the nose and trachea and did not reduce illness. However, the RSV challenge induced a strong secondary antibody response, resulting in very high titres (greater than 8000 reciprocal mean titre) of serum neutralizing antibodies. The poor protective efficacy observed here is discussed with regard to the permissiveness of the chimpanzee to RSV replication, the general requirements for effective immunization against RSV, and the limitations of experimental animals for evaluating candidate RSV vaccines.

Hepatitis C virus shares amino acid sequence similarity with pestiviruses and flaviviruses as well as members of two plant virus supergroups

Hepatitis C virus (HCV) is an important human pathogen that is associated with transfusion-related non-A, non-B hepatitis. Recently, HCV cDNA was cloned and the nucleotide sequence of approximately three-quarters of the virus genome was determined. A region of the predicted polyprotein sequence was found to share similarity with a nonstructural protein encoded by dengue virus, a member of the flavivirus family. We report here that HCV shares an even greater degree of protein sequence similarity with members of the pestivirus group (i.e., bovine viral diarrhea virus and hog cholera virus), which are thought to be distantly related to the flaviviruses. In addition, we find that HCV shares significant protein sequence similarity with the polyproteins encoded by members of the picornavirus-like and alphavirus-like plant virus supergroups. These data suggest that HCV may be evolutionarily related to both plant and animal viruses.

Riboprobe assay for HDV RNA: a sensitive method for the detection of the HDV genome in clinical serum samples

We have used a new hybridization assay for the detection of the genome of hepatitis delta virus (HDV) in serum using a strand-specific RNA probe obtained by transcription of a recombinant riboprobe. This assay was tested on a panel of 30 sera from HBsAg carriers with hepatitis delta antigen (HDAg) in the liver. The riboprobe assay detected HDV RNA in the serum of 83% of the patients, while 63% were positive using the DNA hybridization assay. HDAg was detected in 73% of the same sera by immunoblotting. The riboprobe assay was also compared to other assays on serial samples from an experimentally infected chimpanzee. These results demonstrate that the Northern blot assay using the RNA probe is more sensitive than the homologous DNA probe for the detection of HDV in serum and is also more sensitive than the immunoblot assay for HDAg. The riboprobe assay is the most sensitive of currently available methods to measure HD viremia.

The significance of infections with two types of viral hepatitis demonstrated by histologic features in chimpanzees

In view of the recognized importance of necroinflammatory episodes in chronic hepatitis B virus (HBV) infection, chimpanzees, either HBV surface antigen (HBsAg) carriers or noninfected (naive), were infected with other primary hepatotropic viruses to evaluate histologic alterations and changes in virologic and biochemical markers of infection. The advantages of studies on chimpanzees are the availability of serial biopsy specimens and the viral type-specific histologic lesions, not as well recognized in humans. Infection with hepatitis A and non-A, non-B (NANB) agents produced more severe lesions in chronic HBsAg carrier chimpanzees than in naive animals. During this superinfection, the specific expression of the second agent was predominant, indicating that the exacerbation is caused by the second agent, but that carriers are prone to more severe disease than the naive chimpanzees. Hepatitis delta virus (HDV) infections were always coexistant with HBV and superinfection of carriers produced histologic changes more severe than those seen in any other type of viral hepatitis. Such HDV infections revealed less evidence of lymphocytotoxicity but rather of cytotoxicity, and sometimes resembled in appearance the histopathology of NANB. Coinfection of HDV and HBV and superinfection of HBV-carriers with NANB resulted in hepatitis that was far less severe than superinfection of HDV in HBV carriers, greatly in keeping with human experiences. HBV replication was suppressed transiently in both NANB and HDV superinfection. This implies that in exacerbations during chronic HBV infections of humans, suppression of HBV replication markers indicates superinfection, for instance, by NANB for which markers are so far not widely available; by contrast, elevated markers of HBV replication suggest reactivation of the original HBV infection.

Attenuation and cell culture adaptation of hepatitis A virus (HAV): a genetic analysis with HAV cDNA

RNA transcripts of hepatitis A virus (HAV) HM-175 cDNA from attenuated, cell culture-adapted HAV were infectious in cell culture. A full-length HAV cDNA from wild-type HAV (propagated in marmosets in vivo) was constructed. Chimeric cDNAs that contained portions of both wild-type and attenuated genomes were produced. Oligonucleotide-directed mutagenesis was used to engineer a point mutation into the VP1 gene of attenuated HAV cDNA, so that the sequence of this capsid protein would be identical to that of the wild-type virus. Transfection of monkey kidney cells with RNA transcripts from several of the chimeric cDNAs and from the mutagenized cDNA induced production of HAV. Comparison of the growth of attenuated, wild-type, chimeric, and mutant viruses in vitro indicated that the P2-P3 (nonstructural protein) region is important for cell culture adaptation of the virus; the 5' noncoding region may also contribute to adaptation, but to a lesser extent. Inoculation of marmosets with transfection-derived virus also suggested that the P2-P3 region plays an important role in attenuation of HAV HM-175.

Detection of antibody to hepatitis C virus in prospectively followed transfusion recipients with acute and chronic non-A, non-B hepatitis

We measured antibody (anti-HCV) to hepatitis C virus, which causes non-A, non-B hepatitis, by radioimmunoassay in prospectively followed transfusion recipients and their donors. Of 15 patients with chronic non-A, non-B hepatitis documented by liver biopsy, all seroconverted for the antibody; of 5 with acute resolving non-A, non-B hepatitis, 3 (60 percent) seroconverted. The development of anti-HCV was delayed (mean delay, 21.9 weeks after transfusion, or 15 weeks after the onset of clinical hepatitis) and took approximately one year in one patient. Antibody has persisted in 14 of the 15 patients with chronic disease (mean follow-up, greater than or equal to 6.9 years; maximum, greater than or equal to 12), but has disappeared in the 3 with acute resolving disease after a mean of 4.1 years. Anti-HCV was detected in samples of donor serum given to 14 (88 percent) of the 16 anti-HCV-positive patients for whom all donor samples were available. Only 33 percent of the anti-HCV-positive donors tested had an elevated serum concentration of alanine aminotransferase; 54 percent were positive for antibody to the hepatitis B core antigen (anti-HBc). We conclude that hepatitis C virus is the predominant agent of transfusion-associated non-A, non-B hepatitis and that screening of donors for anti-HCV could prevent the majority of cases of the disease. "Surrogate" assays for anti-HBc and alanine aminotransferase would have detected approximately half the anti-HCV-positive donors involved in the transmission of hepatitis that we identified.

Hepatitis A virus infection in a chimpanzee: duration of viremia and detection of virus in saliva and throat swabs

The pathogenesis of hepatitis A virus was studied by orally inoculating a chimpanzee with wild-type virus. The virus was initially detected in the animal's serum (day 14 after inoculation); then viral antigen was detected in the tonsils (day 16), virus in the saliva and throat swabs (day 18), and viral antigen in the liver (day 21). The animal was viremic for 2 w. While this study involved a single animal, the presence of hepatitis A virus in saliva and throat swabs suggests a possible oropharyngeal site for viral replication.

Cytoplasmic antigen in hepatocytes of chimpanzees infected with non-A, non-B hepatitis virus or hepatitis delta virus: relationship to interferon

We previously described a cytoplasmic antigen, detected by monoclonal antibodies, in hepatocytes of chimpanzees experimentally infected with the parenterally transmitted form of non-A, non-B hepatitis virus or with the hepatitis delta virus. The expression of this antigen appears to be a host-specified response to infection with these two hepatitis viruses but not with hepatitis A virus, hepatitis B virus or enterically transmitted non-A, non-B hepatitis virus. To determine whether this antigen, found in parallel with the hepatocyte cytoplasmic structures described previously, is associated with interferon, as suggested by others, we studied by immunofluorescence liver biopsies from chimpanzees treated with an interferon inducer or exogenous interferon for the presence of the antigen. In two hepatitis B virus carrier chimpanzees and one normal chimpanzee treated with the interferon inducer polyinosinic-polyribocytidylic acid-poly-l-lysine carboxymethylcellulose, the antigen became detectable in hepatocytes within 2 weeks of initiation of the treatment, remained detectable throughout the treatment and disappeared within 4 weeks after treatment was terminated. Electron microscopy revealed that the biopsies positive for the antigen exhibited the hepatocyte cytoplasmic changes; convoluted membranes and microtubular aggregates, identical to those described originally for chimpanzees infected with non-A, non-B hepatitis virus. The antigen was not detected in any of the biopsies from a control chimpanzee that received only the carboxymethylcellulose used to stabilize the interferon inducer. In addition, liver biopsies obtained from a hepatitis B virus carrier chimpanzee during treatment with exogenous human leukocyte interferon were found to be positive for the antigen as well.(ABSTRACT TRUNCATED AT 250 WORDS)