Vol 99, No 6 (2022)

Introduction. The World Health Organization estimates that as of 2019, more than 296 million people were living with chronic hepatitis B virus (HBV) infection. The prevalence of HBsAg-negative, occult form of the disease in blood donors varies depending on the region of the world and the sensitivity of the methods of analysis used. Considering that the genetic diversity of viruses demonstrates space and time variations and taking into account that the genetic profile of isolates in key groups, which may turn into a source of the pathogen spread, is important for forecasting of the epidemiological situation, the attention should be given to identification of HBV genotypes currently circulating among regular blood donors in regions of the Russian Federation.

The aim of this work was molecular and genetic characterization of HBV genomes identified in HBsAg-negative blood donors in the Ural Federal District.

Materials and methods. The study material was 1400 plasma samples obtained from HBsAg-negative blood donors in Ural Federal District. The study included the testing for HBsAg, anti-HBs IgG and anti-HBcore IgG antibodies, HBV DNA. For all identified HBV DNA containing samples, sequencing and analysis of the nucleotide sequences of the complete HBV genomes were performed.

Results. The prevalence of HBV DNA was 4.93%, including 4 (0.28%) cases of false occult hepatitis B. Among anti-HBcore IgG-positive samples, HBV DNA was found in 18.08% of cases, while in persons with detected HBV DNA the anti-HBcore IgG positivity rate was 46.38%. In 8.69% of the isolates, anti-HBs IgG antibodies and viral DNA were detected simultaneously in the absence of anti-HBcore IgG. Based on phylogenetic analysis, HBV subgenotypes distribution in HBsAg-negative blood donors was as follows: D3 — 53.62%, D2 — 21.74%, D1 — 18.84%, C2 — 5.8%. The high variability in the S, C, P regions of the virus genome in the examined group was shown. In all cases of HBsAg-negative chronic HBV infection identified in blood donors, viral sequences contained at least one amino acid substitution in positions, mutations in which are associated with immune escape. In 3 (4.35%) cases mutations in reverse transcriptase region of P gene that are associated with resistance to the following drugs were identified: lamivudine, telbivudine, entecavir. Mutations in the preCore/Core regions that contribute to the progression of liver disease were also identified.

Conclusion. Occult HBsAg-negative chronic HBV infection poses a threat of HBV transmission through transfusion of blood and its components due to the extremely low viral load, which does not allow the virus to be detected using routinely used diagnostic kits. The situation can be exacerbated by the abundance and diversity of virus amino acid substitutions that we have identified, including immune escape mutations, drug resistance mutations, and mutations that contribute to the progression of the disease.

Background. The most effective way to prevent infectious diseases is vaccination. Adjuvants contribute to the optimization of the immune response of vaccines. Double-stranded ribonucleic acids (dsRNAs) from natural sources are promising, but insufficiently studied adjuvants.

The aim of the work was to study the adjuvant activity of dsRNA obtained from the killer strain of Saccharomyces cerevisiae using two models of induction of a specific immune response.

Materials and methods. In the experiments, the substance of the drug Ridostin containing dsRNA, 21.72% (produced by Institute of Medical Biotechnology of the State Research Center of Virology and Biotechnology “Vector”), was used. A specific immune response was modeled using ovalbumin (OVA) or the substance of the EpiVacCorona vaccine (EVC). The experiments were carried out in 200 female BALB/c mice. Mice of the experimental groups were injected twice with antigen and adjuvant together with a 28-day interval, mice of the comparison group — with antigen only. On the 10th day after the second immunization, blood samples were collected to determine the level of specific antibodies using enzyme immunoassay. The results were evaluated by calculation of the average geometric titers of specific antibodies against OVA or EVC.

Results. OVA or EVC administered twice induced the specific antibodies in mice in dose-dependent titers. The combined administration of antigen and dsRNA increased the strength of the immune response. The highest stimulating effect of dsRNA was observed in the dose of 100 µg/mouse administered into mice immunized with OVA (1 µg/mouse) or in the dose of 50 µg/mouse in mice immunized with EVC substance (0.25 of a human dose per mouse).

Conclusion. The data obtained indicate that the substance of dsRNA exerts adjuvant properties, which gives reason to consider dsRNA as a promising adjuvant for peptide vaccines.

Objective. The comparative analysis of the structure of the regulatory gene vasH of the type VI secretion system and its expression in toxigenic and non-toxigenic V. cholerae O1, biovar El Tor strains.

Materials and methods. We used 35 strains isolated from patients and from the environmental samples in the territory of Russia and Ukraine between 1970 and 2017. Analysis of the structure of the vasH gene and the amino acid sequence of the protein was carried out using Ugene 1.32, Mega X, and Bioedit v. 7.0.9.0. The relative level of vasH expression was studied by 2^–ΔΔCt.

Results. The The structure of the vasH gene and the amino acid sequence of VasH protein in toxigenic typical strains and genovariants of V. cholerae O1, El Tor biovar (genotype ctxA+tcpA+) have been shown to be identical to the reference V. cholerae n16961 O1, El Tor biovar strain. The vasH sequence is variable in isolates lacking ctxA and tcpA genes (ctxA–tcpA–), and does not differ from the reference in ctxA–tcpA+ (with the exception of one strain). The studied toxigenic typical strains and the genovariants have a similar relative level of expression of the vasH gene. In isolates that do not contain the ctxA and tcpA genes, the expression of this gene is comparable to toxigenic strains, and is 3.1 times higher in ctxA–tcpA+ strains than that of ctxA–tcpA– and 2.14–2.6 times higher than that of toxigenic ones.

Conclusion. The analysis of toxigenic and non-toxigenic V. cholerae O1, biovar El Tor strains isolated in Russia and Ukraine in different periods of the current cholera pandemic confirmed the data of foreign researchers on vasH gene being intact in toxigenic isolates and variable in isolates lacking ctxA and tcpA genes. Meanwhile, the structure of vasH gene has been shown to be identical to that of toxigenic ones in 99% of the studied ctxA–tcpA+ strains. The expression of the vasH gene has been detected in all studied strains, being the highest in ctxA–TtcpA+ strains. Only two non-toxigenic strains presumably synthesizing the functionally inactive VasH protein have been identified.

Background. H. pylori is the principal causative agent of gastroduodenal disorders in humans. The development and severity of lesions in infected individuals depend on the virulence of H. pylori strains.

Aims: Detection of virulence determinants and comparative analysis of H. pylori genotypes in patients with chronic gastritis (CG) and duodenal ulcer (DU).

Materials and methods. The 53 H. pylori strains were isolated in St. Petersburg from patients with CG (n = 34) and DU (n = 19). The genetic determinants of virulence cagA, iceA, vacA and H. pylori genotypes in patients with CG and UC were determined using the standard PCR method.

Results. The cagA gene was found in 64.1% of H. pylori strains. The proportions of cagA+ isolates from patients with CG and DU was 55.8% (15/34) and 78.9% (15/19), respectively (p > 0.05). The iceA1 allele of H. pylori was detected in 47.4% of patients with DU, the iceA2 — in 47.1% of patients with CG (p > 0.05). The vacAs1 allele was significantly dominant in patients with DU — 94.7% versus 70.6% in CG (p < 0.05). No significant difference in vacA m1 and m2 alleles was found in H. pylori from different groups of patients (p > 0.05). All cagA+ strains were carriers of the vacA s1 allele. The vast majority of strains (10 out of 11) of the cagA–/vacAs2 genotype were isolated from patients with CG.

Conclusion. The significant association between vacAs1, vacAs2 allelic variants, as well as vacA s1/m2, vacA s2/m2 genotypes of the pathogen and severity of clinical manifestations of H. pylori infection has been established in our study. The vacAs1 and vacA s1/m2 genotypes of the pathogen are associated with duodenal ulcer.

Over the past two decades, active study of the microbial ecosystem of the host organism gastrointestinal tract has led to the recognition of gut microbiome as a "key player" that carries a significant immune pressure and is responsible both for the course of physiological processes and for the development of pathological conditions in humans and animals. A vast number of bacteria living in the human gastrointestinal tract are considered as an “organ functioning in dialogue” in formation of immunological tolerance, the regulation of normal functional activity of the immune system and maintaining the intestinal mucosa homeostasis. However, disturbances in interaction between these physiological systems is closely related to the pathogenesis of different immune-mediated diseases. In turn, in a large number of works chronic social stress, along with the use of antibiotics, pre- and probiotics, is recognized as one of the leading factors modulating in the microbiota of the gastrointestinal tract. This review focuses on the role of the gut microbiome in the regulation of immune responses of GALT under stress and modulation of its composition by antibiotics and probiotics administration.