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Biomedical subjects

W F Carman

Publications and source records attributed to W F Carman.

At least 73 records · Page 4Linked to original sources
PubMed1996

Hepatitis B virus envelope variation after transplantation with and without hepatitis B immune globulin prophylaxis.

Hepatitis B virus (HBV) replicates via an intermediate RNA step. High frequency of polymerase errors with additional selection pressure leads to mutations in the HBV genome. We investigated the number, type, and antigenic effects of mutations in the coding region of the HBV surface antigen in eight patients who underwent orthotopic liver transplantation (OLT) for HBV-related end-stage liver disease and were experiencing infection of the graft and who received hepatitis B surface antigen antibody (anti-HBs) prophylaxis (hepatitis B immune globulin [HBIG]) after OLT. Controls were chronic HBV patients who underwent kidney transplantation and received the same immunosuppressive regime but no HBIG. The S-gene was amplified from serum before and after transplantation, sequenced, and changes in the genome were analyzed. In the five patients who experienced reinfection while receiving anti-HBs, clear mutations occurred in the S-gene. In the patient who did not receive HBIG and those who experienced reinfection only after termination of HBIG, no mutations were found in the S-gene. In the kidney recipients, mutations in the S-gene occurred in only one of eight patients. Because the a determinant contains neutralizing epitopes, this region was chosen for antibody binding to quantify antigenic effects of the mutations. The two patients who selected mutations in the a determinant and became reinfected while receiving HBIG had reduced antibody binding after OLT. Our results suggest that HBIG after OLT imposes a selection pressure on the S-gene, and that mutations are one mechanism for reinfection while receiving HBIG.

Amino Acid Sequence↗
PubMed1996

Molecular variants of hepatitis B virus.

Variation in the genome of hepatitis B virus has been associated with a number of clinical parameters, but there is a paucity of functional data to show a causal relationship. For example, variants of the core and X genes have been linked with the pathogenesis of chronic hepatitis, viral replication efficiency, and serologically negative infections, among other observations. Variants of the surface antigen are linked with infection after vaccination, infection of liver grafts in patients undergoing immunotherapy, and samples that react poorly in diagnostic assays.

Amino Acid Sequence↗
PubMed1995

Fulminant reactivation of hepatitis B due to envelope protein mutant that escaped detection by monoclonal HBsAg ELISA.

The detection of a fatal case of reactivation of hepatitis B, in a previously vaccinated Indonesian patient after withdrawal of chemotherapy for lymphoma, was delayed because HBsAg was negative in a widely used monoclonal-antibody-based ELISA. The serum was later found to be strongly reactive for HBsAg by the polyclonal radioimmunoassay and for HBV DNA. PCR sequencing revealed a substitution of arginine for glycine at position 145 of HBsAg in the major neutralising epitope cluster, the a determinant, as well as a 2-aminoacid insertion of asparagine and threonine between positions 122 and 123, immediately upstream of this determinant.

Amino Acid Sequence↗
PubMed1995

Further characterization of 2 types of precore variant hepatitis B virus isolates from Hong Kong.

Two precore variants of hepatitis B virus occur in chronic carriers in the Chinese community in Hong Kong. One variant has a serine at amino acid (aa) 15, and the other has a stop codon at aa 28, which inhibits production of hepatitis B e (HBe) antigen (Ag). The serine 15 strain is shown here to produce antigenically normal amounts of HBeAg. These variants are mutually exclusive, probably due to sequence requirements for encapsidation, and are separate lineages. Sequential core sequences from patients with either variant revealed more aa substitutions in those who have the codon 28 change (P = .02), particularly T helper and B cell epitopes, implying different selection pressures. Most substitutions occurred around the time of selection of the stop codon, implying that complete loss of HBeAg, an immunomodulatory protein, is necessary for immune pressure on core epitopes. Serine 15 strains select small numbers of substitutions throughout the anti-HBe phase, probably because of persistent immunomodulation.

Adult↗
PubMed1995

Hepatitis B e antigen negative chronic active hepatitis: hepatitis B virus core mutations occur predominantly in known antigenic determinants.

In chronic hepatitis B virus (HBV) infection seroconversion from hepatitis B e antigen (HBeAg) to hepatitis B e antibody (HBeAb) may be followed either by remission of the disease with low-level viraemia, or by continuing inflammation with high-level viraemia. In both situations the virus may acquire a mutation in the precore sequence which prevents it from encoding HBeAg. We now show that the number of amino acid substitutions in the HBV core is low in viral sequences from patients with HBeAg positive chronic liver disease and HBeAg negative HBeAb positive patients in remission, but the frequency of substitutions is high in HBeAg, negative HBeAb positive patients with active liver disease. Furthermore we show that these substitutions cluster in the promiscuous CD4+ T-helper-cell epitope and in HBV core/e antibody binding determinants, but are not found in regions recognized by major histocompatability complex (MHC) restricted cytotoxic T lymphocytes. Sequential viral sequences from patients before and after HBeAg/HbeAb seroconversion shows that core mutations arise either at the same time or after the precore stop mutation which prevents the virus from encoding HBeAg. These results are consistent with the hypothesis that after clearance of HBeAg, mutations in regions of the virus recognized by CD4+ helper T cells and B cells allow persistence of the HBe negative virus in HBeAb positive patients with viraemia and active hepatitis.

CD4-Positive T-Lymphocytes↗
PubMed1995

Recombinant vaccinia viruses expressing hepatitis A virus structural polypeptides: detection of an anti-VP0 response in convalescent-phase sera.

We have generated a number of recombinant vaccinia viruses which expressed the hepatitis A virus (HAV) structural polypeptides VP1, VP2, VP3, and VP4, either alone or in combination. The relevant sequences encoding these polypeptides were amplified from cloned cDNA by PCR and then cloned into the insertion vector pGS62. The presence of the HAV structural polypeptide-encoding sequences in the recombinant viruses was confirmed by Southern blot analysis, whilst their transcription and translation were demonstrated by Northern (RNA) blot analysis and immunodetection, respectively. Immunoprecipitation studies using these constructs have detected the presence of an anti-VP0 response in human convalescent sera following HAV infection. The significance of this finding and the usefulness of these constructs in studying cell-mediated immunity during recovery from HAV infection are discussed.

Antibodies, Viral↗
PubMed1995

Variation in the core and X genes of hepatitis B virus.

Variation in viral genomes is dependent upon rates of polymerase error and the relative influence of selection pressures. For HBV, it appears that there is substantial immune pressure in keeping with the immunopathogenesis; the ability of the virus to persist is probably linked with this process. As the viral genome is small, mutants may have multiple effects, particularly apparent within regions that have overlapping functions, such as the encapsidation signal and the X gene. Here, an attempt has been made to correlate variation within the pre-core/core gene with clinical progression and response to interferon and to put forward hypotheses to show the relationship of these mutations to the immune response. Their effects on overlapping regions are also discussed. Little is currently known about the functional importance of mutations within and around the X gene, but it is likely that this will prove a fruitful area of research.

Base Sequence↗
PubMed1995

Hepatitis B virus precore/core variation and interferon therapy.

Precore/core genes from hepatitis B e antigen (HBeAg)-positive and antibody to HBeAg (anti-HBe) positive individuals with active hepatitis have been analyzed to search for correlations with response to interferon before and after treatment. Pretreatment, no precore stop codon mutants were detected, even at the 3% level, in HBeAg-positive responders or nonresponders. In anti-HBe-positive patients, precore mutants did not influence response. No significant core amino acid variability was observed in HBeAg-positive patients, irrespective of interferon response. However, anti-HBe-positive cases had multiple core protein substitutions, mostly in B- ant T-helper cell epitopes, but responders had fewer (P = .02 for responders versus nonresponders and reactivators). None of four responders, three of seven reactivators, and three of three nonresponders had mutations within the major T-helper epitope from aa50 to aa69 (P = .03). Precore mutants appeared in eight of nine natural seroconverters compared with 3 of 10 interferon-induced anti-HBe seroconverters (P = .01). Those in whom precore wild-type remained after treatment often tested negative in the last available sample using polymerase chain reaction (PCR), whereas emergence of mutants led to ongoing viremia in all cases. In anti-HBe-positive cases, precore sequences remained stable during therapy, except for 2 cases in whom a precore mutant appeared accompanied by reactivation. In the core protein, anti-HBe-positive cases selected a mean of 3.5, 1.6, and 1.7 amino acid substitutions in responders, nonresponders, and reactivators respectively (P = NS). In conclusion, core but not precore sequence before therapy may predict response. Appearance of precore mutants during therapy usually predicts failure to clear virus but substitution in core does not influence outcome.

Adolescent↗
PubMed1994

Clinical implications of hepatitis B virus envelope protein variation.

The envelope proteins of hepatitis B virus are highly conserved. They are involved in viral attachment to hepatocytes, virion assembly and secretion and induction of humoral and T-cell immune responses. The major neutralisation epitope is located within the S protein and is conformation dependent, probably due to the formation of disulphide bridges. Variation in the envelope proteins of hepatitis B virus has been described in vaccinees and in patients receiving monoclonal and polyclonal antibody therapy. These arise through point mutations in the surface gene and appear to be selected by the immune response. The emergence of such variants has clinical relevance, in particular with regard to vaccine failure and diagnostic difficulties.

Amino Acid Sequence↗
PubMed1994

Molecular characterization of envelope antigenic variants of hepatitis B virus from Spain.

In a survey of hepatitis B virus (HBV) subtypes using one set of monoclonal typing antibodies, 96.6% of the samples were ad or ay and 3.3% (31) were untypeable. Using two additional antibody panels, 23 samples were ay and ad. Six samples required a third panel to be typed as ay. One sample was not typeable. These last 7 samples were nonreactive or had low reactivity with some antibodies to the common a determinant. Sequencing the HBsAg gene of these 7 samples revealed that amino acid (aa) 122 was arginine, as expected for the y determinant. However, mutations giving rise to serine at aa 120, leucine at aa 143, and glutamic acid at aa 144 were found singly or in combination and correlated with the monoclonal antibody binding patterns. These results have implications for further subtyping surveys, vaccines, immunotherapy, and the design of diagnostic assays, and they give clues to the structure of the major neutralizing epitope of HBV.

Amino Acid Sequence↗
PubMed1994

Envelope and precore/core variants of hepatitis B virus.

The appearance of replication-competent variants of HBV with mutations in the envelope and precore/core and X proteins emphasizes that these proteins are the focus of immune selection pressures in the human host. The presence of an antibody response in the absence of a CTL response may create the ideal selection environment. This occurs in the early phase of passive/active immunization against HBV envelope proteins in neonates born to HBV-infected mothers and also during the emergence of HBeAg-negative variants during and after HBe antigen/antibody seroconversion in chronic HBV carriers with defective CTL responses. The sequence and speed of application of the multiple selection pressures (humoral and possibly cellular) determine the virologic and clinical outcome. When these variant viruses are passed to a new host, in the absence of the immune selection pressures or modified immune pressures that resulted in their selection, a picture clinically different from that seen in the original host may emerge.

Acute Disease↗
PubMed1992

Effect of cyclosporin-A in woodchucks with chronic hepatitis delta virus infection.

Four woodchucks chronically infected with hepatitis delta virus (HDV) were treated with cyclosporin-A (CyA) for 11 weeks. All animals had detectable HDAg in the liver and two of them were also positive for HDAg and HDV-RNA in serum. Reappearance of HDV in serum was noted in one of the two non-viraemic animals and increased viraemia in the two viraemic. HDV-RNA levels became elevated within a week of starting treatment and an inverse relationship between HDV-RNA and WHV-DNA became apparent during the treatment period. With discontinuation of treatment, HDV-RNA levels either returned to pretreatment levels or became negative. The remaining animal showed no return of viraemia during CyA treatment; HDV-RNA remained negative and WHV-DNA levels did not change. Liver biopsies revealed a slight increase in lobular activity during CyA treatment in the animals showing increased viraemia. These data are consistent with the hypothesis that the host immune response exerts a negative control on the level of HDV viraemia and that HDV influences HBV replication independently of the host immune response. In an animal that may have been clearing HDV, immunosuppression did not result in recurrence of viraemia.

Animals↗
PubMed1992

Precore sequence variation in Chinese isolates of hepatitis B virus.

Direct sequencing of polymerase chain reaction-amplified serum hepatitis B virus (HBV) DNA was used to characterize the precore region of HBV from Chinese patients with chronic hepatitis. Two types of mutually exclusive variants were found in hepatitis B e antigen (HBeAg)-negative patients. The first (M1) contains a substitution from proline to serine at codon 15. A second group were infected with a previously described mutant (M2) containing a translational stop codon. HBeAg-positive patients were infected with the wild-type virus or the M1-containing strain. M2 emerged in patients with wild-type infection after seroconversion to anti-HBe, whereas M1 was present during the HBeAg-positive phase. In those with fluctuating HBe status, there was no correlation between prevailing HBe serology and sequence. There was an association between infection with variants and severe chronic hepatitis. Patients infected with strains containing M1 while HBeAg positive had a worse prognosis after seroconversion to anti-HBe.

Alanine Transaminase↗
PubMed1992

The host immune response may be responsible for selection of envelope and precore/core variants of HBV.

The appearance of replication-competent variants of HBV with mutations in the envelope and precore/core proteins emphasizes that these proteins are the focus of immune selection pressure in the human host. The sequence and speed of application of the multiple selection pressures (humoral and possibly cellular) will determine the virological and clinical outcome. When these variant viruses are passed to a new host, in the absence of the immune selection pressures or modified immune pressures which resulted in their selection, a clinical picture different from that seen in the original host may emerge. Although HBV would seem to be highly evolved, it still seems to have the capacity for further diversity. A number of the reported variations have an obvious clinical relevance, but others do not, and further study is required to elucidate their importance. Whether they represent independently transmissible strains of HBV or are all selected during the course of infection, only to be lost in favor of the original strain on infection of another host, also remains to be determined.

Genetic Variation↗
PubMed1991

Incidence of hepatitis B viraemia, detected using the polymerase chain reaction, after successful therapy of hepatitis B virus carriers with interferon-alpha.

Thirty-nine patients (62 sera) who, after interferon-alpha therapy for chronic hepatitis B virus (HBV) infection, were seronegative for HBeAg and HBV-DNA by dot blot hybridisation, were tested using the polymerase chain reaction (PCR) for residual viraemia. Overall, 59% of the HBsAg-positive sera and 43% of the HBsAg-negative sera were positive by PCR. All except one of the HBsAg-negative patients had seroconverted to anti-HBs. Between 13 and 18 months after therapy, 33% of the HBsAg-positive and 20% of the HBsAg-negative patients remained viraemic. Eighteen months after the end of treatment, no patient tested was positive. Twenty-three patients were tested sequentially over periods from 1 to 43 months: Thirteen lost HBV-DNA by PCR, three remained positive, five remained negative, and two patients relapsed. The merits and disadvantages of PCR for assessing interferon treatment of HBV carriers are discussed.

Base Sequence↗