[HBs antigen mutants: prevalence, clinical and diagnostic implications]. / Les mutants de l'antigène HBs: prévalence, impact diagnostique et clinique.

The serological diagnosis hepatitis B (HBV) infections relies mainly on the detection of the small surface antigen (HBsAg). Immuno-enzymatic assays use antibodies directed against epitopes of the major hydrophilic region, in particular against a determinant. Genetic variants have been detected in vaccinated children, liver transplanted patients receiving anti-HBs immunoprophylaxis and chronic carriers with an occult infection (negative HBsAg). Substitutions in this region can induce conformational changes abolishing some diagnostic antibodies binding leading to false negative results. To estimate the prevalence of such substitutions, we studied 55 sequences of the gene S obtained between 2002 and 2004, carried out mainly in the search of changes of resistance to the lamivudine. The polymorphism of the major hydrophilic region (positions 102 to 169) was studied using Mutation Master software. Each sequence was compared with a consensus sequence of the same genotype. Genotype distribution is as follows: D, 40%; With, 20%; C, 16%; B, 11%; E, 9%; F, 2% and G, 2%. Changes I195 M and W196L, reflecting lamivudine resistance are present among 18 patients (33%). Substitutions of the major absorbent area are found among 31 patients (56%), of which a third associated with resistance mutations. The most frequent substitutions involved the following amino-acids: F/Y134 (7/31), M133 (6/31), D144 (6/31) and G145 (6/31). These two latter are known to be associated anti-HBs immunoglobulins or vaccine escape. BLOSUM scores are indicative of substitutions inducing important changes of physicochemical properties in 16 patients (29%). Such substitutions could thus potentially alter the binding of antibodies used in diagnostic assays. In conclusion, changes of the major hydrophilic loop of HBs antigen are not rare and could have an important implications for transfusion safety and diagnostic reliability.

Performance of TRUGENE hepatitis C virus 5' noncoding genotyping kit, a new CLIP sequencing-based assay for hepatitis C virus genotype determination.

The performance of the recently developed, standardized direct sequencing assay for hepatitis C virus (HCV) genotyping [TRUGENE HCV 5'-NC (noncoding)] was assessed in comparison with the reverse hybridization-based assay INNO-LIPA HCV II. Both assays allow HCV genotyping starting from amplification products generated by the diagnostic Roche AMPLICOR HCV test. HCV amplicons from 205 patients were used for this study: 34 were tested prospectively by both methods, while 171 had been stored at -20 degrees C for up to 2 years after LiPA genotyping. The TRUGENE procedure failed to determine a genotype in six low-titered samples (3.5 +/- 0.3 log UI/mL vs. 5.2 +/- 0.5 UI/mL for typable samples). Type and subtype could be determined by sequencing for 199 samples (97%). Among them, five were considered as coinfections by the LiPA method. Three LiPA patterns suggesting type 1 and 4 coinfection were not supported by sequence analysis while one 1a/2b and one 1a/3a coinfection was backed up by direct sequencing. For the remaining 194 samples, type assignment was concordant in 100% of the cases. LiPA subtyping was available for 162 samples (83.5%). Sub-typing results concurred in 128 cases (79%). NS5B sequencing of discrepant samples underscored the limitation of the 5'-noncoding region (NCR) in correct subtype assignment. In conclusion, the TRUGENE HCV 5'-NC genotyping kit appeared to be a specific and reliable method that can be used in the current indication of HCV genotyping.

Performance of an automated system for quantification of hepatitis C virus RNA.

The Amplicor HCV Monitor test for quantitative determination of serum or plasma hepatitis C virus (HCV) RNA was modified recently and introduced onto the Cobas Amplicor instrument to automate fully amplification, detection and calculation of results. This new version (v2.0) was evaluated in a routine diagnostic laboratory. The sensitivity and reproducibility were assessed on well-characterized panels (Eurohep) and clinical samples. HCV RNA levels measured by the v2.0 Monitor test were about 1log(10) higher than those detected by the previous version test, and genotypes 1 and 3 were quantified with equal sensitivity. Within the linear dynamic range of 10(3) to 10(6) copies/ml, the coefficients of variation for both intra- and inter-assay reproducibility ranged from 1.9 to 2.95%. This test system was found to be a reliable and labor saving assay for the quantification of HCV RNA.