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Biomedical subjects

K Colman

Publications and source records attributed to K Colman.

5 recordsLinked to original sources
PubMed1997

Hepatitis B virus core protein mutations are concentrated in B cell epitopes in progressive disease and in T helper cell epitopes during clinical remission.

The distribution and temporal and clinical features of amino acid substitutions of the core protein of hepatitis B (HB) virus were analyzed, using at least 2 sequential samples from 27 patients. Six patients seroconverted from HBe antigen (HBeAg)-positive to anti-HBe-positive (3 went into remission), and 21 were continuously anti-HBe positive with progressive hepatitis. Precore mutations, which terminate HBeAg translation, all appeared by the second sample. Most core mutations occurred between the first and second samples; significantly fewer occurred after the second. In seroconverters who went into remission, mutations occurred in the T helper epitope from aa 50 to 69 (P = .00045); for anti-HBe-positive patients with ongoing disease, mutations occurred in B cell epitopes (P = .0007 for aa 74-83). An ineffective anti-HBc B cell response accounts for ongoing disease and selection of mutations after seroconversion. In those who remit, mutations in the major T helper epitope allow immune escape, thus minimizing immune-mediated hepatitis.

Adult↗
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↗
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

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↗