Non-A, non-B hepatitis: is there more than a single blood-borne strain?

Hepatitis C virus-specific CTL responses in PBMC from chimpanzees with chronic hepatitis C: determination of CTL and CTL precursor frequencies using a recombinant canarypox virus (ALVAC)

The aim of this study was to evaluate HCV-cytotoxic T lymphocyte response from PBMC in bulk CTL assays and in CTL precursor analyses using in vitro stimulation with canarypox virus (ALVAC) expressing HCV-capsid/E1/E2/NS2/NS3 antigens. Canarypox virus is naturally host-range restricted and does not replicate or cause cytopathology on mammalian cells. PBMC were obtained from four chimpanzees with chronic hepatitis C infection and one uninfected chimpanzee. CTL from bulk culture of PBMC and CTL precursor frequencies were found in three of the four chronically infected chimpanzees using ALVAC in vitro stimulation. No CTL response was detected in PBMC from the uninfected chimpanzee. The precursor frequencies of CTL specific for capsid, NS2 and NS3 proteins ranged between 1/2663 and 1/27202. No correlation was observed between percent cytolysis in bulk culture and CTL precursor frequencies. This method may prove useful in assessing the correlation between HCV-CTL response and virological or histological status.

Visualization of hepatitis C virions and putative defective interfering particles isolated from low-density lipoproteins

Hepatitis C virus (HCV) in highly infectious sera has been shown to be predominantly associated with low-density lipoproteins. To determine whether the association is specific to low-density lipoproteins (LDL) or very low-density lipoproteins (VLDL), we fractionated HCV-containing plasma by a column chromatographic procedure known to separate these classes. Hepatitis C virus RNA detected by polymerase chain reaction (PCR) was associated primarily with the very low-density (VLDL) fraction. However, it could not be ruled out that virus-associated LDL may have eluted with this fraction. Hepatitis C virus virions isolated from sera having sufficient titre for visualization by electron microscopy are generally coated with antiviral antibodies, therefore we utilized the lipid association to isolate antibody-free virions. Very low-density lipoproteins were isolated by ultracentrifugal flotation and then treated with deoxycholate to release the virions. These were then isolated in a highly purified form by centrifugation in a sucrose gradient. The 1.10-1.11 g ml-1 region of the gradients contained 60-70 nm particles. Particles with similar surface structure but having a diameter of only 30-40 nm constituted about 30% of the total. The latter may represent defective interfering particles. The identity of both small and large particles with HCV virions and associated particles was confirmed by their trapping on grids by an anti-HCV E2 monoclonal antibody, and by their aggregation by rabbit antiserum to an amino-terminal peptide of E1. Thus, both E1 and E2 epitopes are displayed on the surface of intact HCV virions.

Isolation of novel virus-like sequences associated with human hepatitis

Two viruses, GB virus A (GBV-A) and GB virus B (GBV-B), were recently identified in the GB hepatitis agent. Human sera containing antibodies that recognize GBV-A and/or GBV-B recombinant proteins were subjected to polymerase chain reaction studies with degenerate oligonucleotides capable of amplifying a segment of the putative helicase genes from GBV-A, GBV-B or hepatitis C virus. Novel sequences related to members of the Flaviviridae were identified in sera from 12 individuals including 4 individuals with hepatitis. The limited nucleotide sequence identity between GBV-A, GBV-B and HCV sequences suggests that a novel virus, tentatively named GB virus C, may be responsible for some cases of non-A, non-B, non-C, non-D, non-E hepatitis.

Immunity in hepatitis C virus infection

Immunity after HCV infection is weak, even after reinfection with the identical strain of virus. Even chronically infected chimpanzees can be reinfected. Weak immunity may reflect the fact that HCV virions are coated with lipoproteins (VLDL), preventing antibody binding. This phenomenon presents a serious challenge for development of vaccines.

Hepatitis C virus: historical perspective and current concepts

Over the past 30 years, hepatitis C has emerged from shadowy enigma to important public health problem. The existence of the etiological agent of this disease was first appreciated two decades ago but significant progress in its understanding had to await its molecular characterization within the past 5 years. The virus is a member of the family Flaviviridae and is the cause of approximately 20% of clinical viral hepatitis in the United States. While the control of the transmission of hepatitis C virus in blood and blood products has been nothing less than spectacular, the control of community-acquired hepatitis C will be a major challenge to the scientific and medical communities.

A study of primary- and re-infection with hepatitis C virus in blood transfusion recipients

A nested polymerase chain reaction was used to assess viraemia in blood transfusion recipients with no serological evidence of hepatitis C virus (HCV) infection (naive recipients) and in recipients with prior or existing HCV infection (infected recipients), who were transfused with HCV-positive blood. In 10 hepatitis cases in naive recipients, defined as primary infection, nine showed clinical hepatitis, and one was sub-clinical; the time between transfusion and elevation of alanine aminotransferase (ALT) levels was 15-60 days (37.9 +/- 13.9). All 10 naive recipients showed abnormal ALT, and 10/10 and 7/10 were persistently positive for anti-HCV and HCV-RNA, respectively, for more than 1 year. Similarly, in five cases in previously infected recipients, defined as re-infection, 4/5 showed clinical hepatitis, the time to elevation of ALT was 30-46 days (34.8 +/- 6.4), and 5/5 and 3/5 were persistently positive for anti-HCV and HCV-RNA, respectively, for more than 1 year. All five infected recipients showed abnormal ALT. In conclusion, there was no significant difference (P = 0.05) in the frequency of the markers of infection resulting from primary or re-infection with HCV, suggesting that primary infection fails to induce a protective immune response.

An ultrastructural study of six cases of chronic active C hepatitis. A comparison with chronic active B hepatitis

Liver biopsies from six patients affected by chronic active hepatitis (CAH) induced by hepatitis C virus (HCV) have been investigated ultrastructurally and their features compared with those of five cases of CAH induced by hepatitis B virus (HBV). Clusters of deeply packed nuclear inclusions (18 to 22 nm in diameter) were found in patients with HCV-CAH. They were irregularly round and ill-delimited. These inclusions were distinct from the regular round and well-delimited nuclear inclusions associated with HBV. HCV-associated nuclear inclusions were similar to a peculiar type of intranuclear particle described in non-A, non-B hepatitis before the HCV disease had been recognized as a distinct entity. These inclusions have never been hitherto reported in infections caused by HBV or other known hepatotropic viruses. Together, these data suggest that the occurrence of these inclusions can be related to HCV activity in hepatocytes. Changes in the microarchitecture of the liver cell and its microenvironment were similar in HCV- and HBV-CAH. They were heterogeneous in different cases and did not display a clear correlation with the severity of the disease.

Lack of protective immunity against reinfection with hepatitis C virus

Some individuals infected with hepatitis C virus (HCV) experience multiple episodes of acute hepatitis. It is unclear whether these episodes are due to reinfection with HCV or to reactivation of the original virus infection. Markers of viral replication and host immunity were studied in five chimpanzees sequentially inoculated over a period of 3 years with different HCV strains of proven infectivity. Each rechallenge of a convalescent chimpanzee with the same or a different HCV strain resulted in the reappearance of viremia, which was due to infection with the subsequent challenge virus. The evidence indicates that HCV infection does not elicit protective immunity against reinfection with homologous or heterologous strains, which raises concerns for the development of effective vaccines against HCV.

Temporal relationships of hepatitis C virus RNA and antibody responses following experimental infection of chimpanzees

Liver enzyme levels, viral RNA, and the immune response against both structural and nonstructural hepatitis C virus (HCV) proteins have been studied in experimentally infected chimpanzees in order to further understand the natural history of HCV infection. An ELISA for measuring both IgG and IgM responses to core (c22), 33c (NS3), and c100 (NS4) was employed. The IgG response rates were 5/8 for core, and 8/8 for both 33c and c100. Utilizing this antigen combination, at least one antibody response is measureable at, or within 3 weeks of, the major ALT peak. Although no individual antibody response is universally associated with initial detection of seroconversion, the combination of all three recombinant proteins measures seroconversion an average of 54 days earlier than with c100 alone, in 6/8 of the animals. IgM responses were measureable in 5/8 of the chimpanzees, were of shorter duration, and usually arose concomitantly with IgG responses. IgM appears to be a good indicator of primary infection since neither boosting nor recrudescence of disease during the chronic phase of disease elicited a secondary IgM response. Viral RNA can be measured 4-7 days (average = 9 days) postinfection with the period preceding the ALT peak being characterized by several PCR positive segments interrupted by periods in which no viral RNA can be measured. Following the ALT peak, chronically infected animals with recurring ALT elevations are generally PCR positive with intercedent PCR negative periods. Those animals that appear to have biochemically resolved disease generally have PCR negative profiles, although they still may periodically exhibit PCR positive sera. This indicates that with the recent advent of new screening techniques, a more stringent definition of HCV resolution will be required.

Long-term follow-up of chronic hepatitis non-A, non-B--with special reference to hepatitis C

One hundred and twenty-seven patients with histologically verified chronic non-A, non-B hepatitis were followed for up to 23 years (mean 6.3 years). Thirty-nine were infected by blood transfusion, 58 were drug-addicts and 30 had no obvious source of infection. Chronic persistent hepatitis (CPH) was diagnosed in 84 (66%), while 43 patients (34%) had chronic active hepatitis (CAH) with or without cirrhosis. Patients with CPH were significantly younger (29.7 years vs 46.8 years; p less than 0.01), irrespective of the type of virus exposure. Antibodies to hepatitis C virus (anti-HCV) were detectable in 91 patients (72%) and 36 (28%) were anti-HCV negative. Fifteen patients with acute onset, and negative for anti-HCV at the start, became positive during follow-up; 12 of them within 4.5 months. We found no differences among anti-HCV positive and anti-HCV negative patients in liver function tests, resolving rate, morphological progression in serial biopsies or mortality rate. Five previously anti-HCV positive patients became negative during follow-up and in two of them this was accompanied by decreasing hepatic inflammation.

Establishment of a human T-cell clone cytotoxic for both autologous and allogeneic hepatocytes from chronic hepatitis patients with type non-A, non-B virus

A human T-cell clone (TA-NB-2) that could lyse both autologous and allogeneic hepatocytes from chronic hepatitis patients with type non-A, non-B virus (NANB) was established. This clone produced CD3+ CD8+ cytotoxic T lymphocytes and expressed an antigen specific for alpha and beta subunits of T-cell receptor. The cytotoxic activity of the clone was abrogated by incubation with anti-CD3 monoclonal antibody. Anti-HLA monoclonal antibodies did not block the lysis of the target hepatocytes by TA-NB-2 cells. The cytotoxicity of TA-NB-2 clone against hepatocytes from patients with chronic NANB hepatitis was 39.8 +/- 13.2% (mean +/- SD; n = 17) (range, 14.2-60.5%), whereas that against hepatocytes from control patients with chronic type-B hepatitis, acute hepatitis B, acute hepatitis A, or alcoholic liver cirrhosis was 4.0 +/- 7.7% (n = 12) (range, -10.8 to 14.0%). The results suggest that TA-NB-2 cells specifically recognize a hepatitis NANB-related antigen expressed on hepatitis NANB-infected hepatocytes by T-cell receptor and that the recognition is not restricted by the major histocompatibility complex antigens. The results also suggest that most, if not all, cases of chronic hepatitis due to NANB are caused by one agent; TA-NB-2 clone may be useful as a tool to identify this particular hepatitis-related antigen.

An outbreak of suspected water-borne epidemic non-A non-B hepatitis in northern Botswana with a high prevalence of hepatitis B carriers and hepatitis delta markers among patients

From June to December 1985 273 cases of hepatitis and jaundice were diagnosed in Maun, northern Botswana. It was known before the outbreak that most adults were immune to hepatitis A virus, most had markers indicating past infection with hepatitis B virus (HBV), there was a mean prevalence of 13.6% (57/418) HBsAg carriers, and a proportion of people had antibodies to hepatitis delta virus (HDV). There was evidence that faecal contamination of water supplies preceded the outbreak; the epidemic curve suggested that there was a major common source of infection; the disease appeared to have affected 1-2% of the population; 90.3% (214/237) patients for whom information is available were aged 20 years or older; the disease was generally mild and affected pregnant women most severely. 49 patients were admitted to hospital and at least 4/273 died. There were prevalences of 47% (28/60) HBsAg and 69% (37/54) anti-HDV reactors among patients bled 1-43 d after the onset of illness. The main features of the outbreak conformed to published descriptions of water-borne epidemic non-A non-B hepatitis and it is postulated that the disease was most severe in patients with active HBV infection and in those with HDV superinfection, so that such patients were disproportionately represented amongst those seeking medical attention.

Non-A, non-B hepatitis

Diagnosis of non-A, non-B hepatitis (NANB) is made after exclusion of other known causes of hepatitis. Parenterally spread non-a, non-B hepatitis (PNANB) and enterally transmitted non-A, non-B hepatitis (ENANB) almost certainly appear to be two different diseases. The definite causative agents have not hitherto been identified. Much of our knowledge of NANB is based on (i) experimental studies on chimpanzees; and (ii) epidemiological studies. Parenterally spread non-A non-B hepatitis caused by whole blood transfusion and blood-product infusion has different incubation periods and may be caused by different agents. It is a mild disease clinically, and the majority of the patients are asymptomatic. It can be prevented only by judicious use of blood transfusion. Whenever possible, blood/blood products should be derived from individual volunteer donors who are anti-HBc sero-negative and have serum alanine transaminase of under 45 IU/l. Enterally-transmitted non-A non-B hepatitis is endemic in the Indian subcontinent, South-East Asia, North and East Africa and Latin America. Epidemic NANB is usually transmitted by water supply contaminated with feces. ENANB has a predilection for young adults. The disease is usually mild, except in pregnant women, who have a high case-fatality rate from fulminant hepatic failure. Control measures include provision of clean water supplies, safe disposal of human excreta and sound personal and food hygiene practices.

Rationale for surrogate testing to detect non-A, non-B hepatitis

NANB hepatitis was initially recognized in 1975 and 13 years later, the exact etiology of this presumed viral disease remains uncertain. The acute illness is relatively mild with only about 25% of patients becoming icteric. Nevertheless, at least one half of the patients have evidence of chronic infection, and, as recently recognized, 10% to 20% develop severe liver disease. Because approximately 2% of patients who receive transfusions and whose underlying medical condition permits long term follow-up develop posttransfusion hepatitis, procedures for reducing this risk are considered prudent. Unfortunately specific tests for detecting NANB hepatitis are not available, and it is unlikely that such tests will be available in the near future. Hence, testing by surrogate or nonspecific tests (ALT and anti-HBc) were recommended because evidence from two studies conducted during the 1970s showed these tests identify some donors thought to transmit the infection. However, randomized, controlled prospective studies to determine whether these tests will, in fact, reduce NANB posttransfusion hepatitis were not performed. By the mid-1980s it was apparent these studies would not be performed nor were studies to determine the incidence of NANB posttransfusion hepatitis in the post-AIDS screening era likely to be initiated. Therefore, surrogate testing, as the best available method for reducing posttransfusion hepatitis, was implemented in the United States in 1986-87.

Alpha-interferon therapy for non-A, non-B hepatitis transmitted by gammaglobulin replacement therapy

Three hypogammaglobulinaemic patients with non-A, non-B hepatitis transmitted by gammaglobulin replacement therapy were treated with lymphoblastoid alpha-interferon. All showed a striking improvement in serum aminotransferases after the start of each course of treatment.

Non-A, non-B hepatitis: an update

The definition of non-A, non-B hepatitis (NANB) is improved by further characterization of what it is not (like the delta agent or non-A epidemic hepatitis) rather than by providing convincing evidence of isolation of the agent responsible for blood transfusion- or blood product-related NANB or specific markers thereof. Yet, NANB research is in disquieting movement. Modern biotechnology yielded its blessings to the field. However, monoclonal antibodies and molecular probes will have to be evaluated with the same scrutiny that unmasked so many test systems and viral agents thus far. Recent victims appear to be published reports on NANB being identified as a retroviral agent and NANB virus being propagated in primary cultures of chimpanzee hepatocytes. Yet the application of these powerful new tools, together with the availability of cultured human and chimpanzee hepatocytes for propagation of the agent may improve the chances for substantial progress. Our finding of involvement of lymphocytes in transmission of the disease may add another approach to reach the ultimate goal of characterization of the causative agent and development of diagnostic methods to detect it in patients and biological materials derived from carriers of the disease.