Synthetic peptides in the determination of hepatitis A virus T-cell epitopes

Evidence of Circulation of Several HAV Genetic Variants and Emergence of Potential Antigenic Variants in an Endemo-Epidemic Country before Vaccine Introduction

Similar to several other countries in the world, the epidemiology of hepatitis A virus changed from high to intermediate endemicity level in Tunisia, which led to the occurrence of outbreaks. This study aimed to determine the genetic and antigenic variability of HAV strains circulating in Tunisia during the last few years. Genotyping using complete VP1 gene and VP1-2A junction confirmed the predominance of genotype IA, with co-circulation of several genetic and antigenic variants. Phylogenetic analysis including Tunisian and strains from other regions of the world showed the presence of at least two IA-variants within IA subgenotype. Amino-acid analysis showed several mutations in or close to epitope regions in the VP1-region. This study provides a baseline on the genetic and antigenic variability of HAV circulating strains before the introduction of vaccination into the national immunization schedule.

Detection of hepatitis A virus genotype IB variants in clams from Maputo Bay, Mozambique

Clams provide an important source of food and income for the population of Maputo, Mozambique, where conditions of poor water supply and inadequate sanitation favor endemic infection with hepatitis A virus (HAV). To determine the role of bivalves in an endemic area, clams gathered from Maputo Bay were bought from market and examined for HAV. Four batches, total 150 clams, were sampled over the year. RNA extracted from individual digestive glands was assayed by nested RT-PCR and sequencing of HAV 5' noncoding region (5' NCR). Specific HAV signals were detected in one batch, 23 of 34 clams (67%) testing positive. Phylogenetic analyses of VP3/VP1, VP1/P2A, and 5' NCR determined clustering of clam strains as genotype I, subtype B. In addition to identifying HAV IB strains with predicted conserved amino acid sequence, IB variants exhibiting novel amino acid substitutions at the VP1/P2A junction were detected. HAV strains from clams showed 93%-99% homology with wild-type IB strains from South African outbreaks and from a panel of HAV IgM positive Swedish patients. DNA from enteric human adenovirus 40/41 was found in a limited number of clams from two batches, 6/34 (17%) and 4/35 (11%). Detection of HAV subgenotype IB in bivalves provided indirect evidence of the strains circulating in a densely populated coastal region where HAV is presumed to be hyperendemic. The results suggest that clams may be an important source of HAV in Maputo region, and indicate the need for further molecular study of strains circulating in the indigenous population.

Genome variability and capsid structural constraints of hepatitis a virus

The number of synonymous mutations per synonymous site (K(s)), the number of nonsynonymous mutations per nonsynonymous site (K(a)), and the codon usage statistic (N(c)) were calculated for several hepatitis A virus (HAV) isolates. While K(s) was similar to those of poliovirus (PV) and foot-and-mouth disease virus (FMDV), K(a) was 1 order of magnitude lower. The N(c) parameter provides information on codon usage bias and decreases when bias increases. The N(c) value in HAV was about 38, while in PV and FMDV, it was about 53. The emergence of 22 rare codons in front of 8 in PV and 7 in FMDV was detected. Most of the conserved rare codons of the P1 region were strategically located at the carboxy borders of beta barrels and alpha helices, their potential function being the assurance of proper folding of the capsid proteins through a decrease in the translation speed. This strategic location was not observed for amino acids encoded by the conserved rare codons of the 3D region. The percentage of bases with low pairing number values was higher in the latter region, suggesting a role of the conserved rare codons in the maintenance of RNA structure. Many of the rare codons in HAV are among the most frequent in humans, unlike in PV or in FMDV. This fact may be explained by the lack of cellular shutoff in HAV. One hypothesis is that HAV has evolved in order to avoid competition with its host for cellular tRNAs.

Molecular characterization of hepatitis a virus isolates from a transcontinental shellfish-borne outbreak

One hundred eighty-four serologically confirmed cases of hepatitis A were reported in eastern Spain in 1999. A matched case-control study implicated imported coquina clams complying with European Union shellfish standards as the source of infection; this implication was confirmed by the detection by reverse transcription-PCR of hepatitis A virus (HAV) RNA in shellfish samples. In spite of the recognized low variability of HAV, genetic characterization of the complete capsid region of virus isolates from patient serum samples revealed the existence of both synonymous and nonsynonymous variants. Two antigenic variants were detected, one in a discontinuous epitope defined by monoclonal antibody K3-4C8 and a second in a linear VP1 epitope of the virus. In spite of these antigenic variants, all isolates were assigned to genotype IB, providing further evidence that the outbreak originated from a common source, although multiple strains were likely to be involved.

Synthesis, lipophilic derivatization and interaction with liposomes of HAV-VP3 (102-121) sequence by using spectroscopic techniques

Hepatitis A virus (HAV) is composed mainly of three structural capsid proteins: VP1, VP2 and VP3. Our group has reported the synthesis and the immunogenic evaluation of VP3 (110-121) peptide sequence. In the present work, in order to stimulate a T-cell immune response, we have selected the HAV-VP3 (102-121) peptide which has maximum amphipathicity. Its synthesis was carried out manually in the solid phase and semipreparative HPLC was used for purification of the crude peptide. Finally the purified peptide was characterized by analytical HPLC, amino acid analysis and MS. A palmitoyl derivative of VP3 (102-121) was synthesized to modify the hydrophobicity of the peptide. Both free and lipophilically derivatized peptides were incorporated into multilamelar liposomes. Physicochemical studies of the HAV-related peptides described above were carried out using monolayers as membrane models. Compression isotherms, surface activity and penetration kinetics into dipalmitoylphosphatidylcholine monolayers were determined. Moreover, changes in the fluidity of bilayers induced by these peptides were determined by means of polarizable probes such as 8-anilino-1-naphthalenesulfonic acid and 1,6-diphenyl-1,3,5-hexatriene. The integrity of the membranes has also been ascertained with the carboxyfluorescein.

Localization of a sequential B-epitope in the VP2 protein of hepatitis A virus

A set of synthetic peptides derived from the capsid protein of hepatitis A virus was used to search for B-epitopes. Peptides from the 115-139 region of the VP1 protein, from the 69-99 region of the VP2 protein and peptide 137-150 from the VP3 protein were found to react with monoclonal and polyclonal anti-HAV antibodies. MAPs based on 64-80 and 66-80 fragments of VP3 were reactive as well. Peptides, their conjugates with protein carriers and MAPs were used for antipeptide antibody production. Only free peptide 69-99 from the VP2 protein caused formation of HAV binding antibodies.