[Effect of Point Mutations in the Polymerase Genes of the Influenza A/PR/8/34 (H1N1) Virus on the Immune Response in a Mouse Model].

The vaccine strains for live attenuated influenza vaccines (LAIVs) have cold-adapted, temperature-sensitive, and attenuated phenotypes, which are guaranteed by the presence of specific mutations from the master donor virus in their internal genes. In this study, we used mutant viruses of the pathogenic A/Puerto Rico/8/34 (H1N1) that contained ts-mutations in PB1 (K265N, V591I), PB2 (V478L), and PA (L28P, V341L) genes along and/or in different combinations to evaluate the impact of these mutations in the immune responses. Sequential addition of tested mutations resulted in the stepwise decrease in virus-specific serum and, to a lesser extent, mucosal antibody levels. We demonstrated strong positive correlation between virus attenuation (virus titer in lung) and antibody titers. The ts-mutations in PB1, PB2, and PA genes are mostly involved in the modulation of the humoral immunity, but also have a moderate effect on the cellular adaptive immune response.

[Local antibody immune responses in influenza patients and persons vaccinated with seasonal, pre-pandemic, and pandemic live attenuated influenza vaccines].

Mucosal immunity is one of the most important factors of human anti-influenza defense. The data about local immune responses in influenza A (H3N2) patients and in persons vaccinated within 2000-2009 with different seasonal LAIVs, A (H1N1)pdm2009 LAIV, and A (H5N2) LAIV are discussed. The influenza infection resulted in the larger quantities of local IgA and IgG conversions than seasonal LAIV vaccination. 56% of young (18-21 y.o.) persons had high titers (> or = 1:64) of IgA to A (H1N1)pdm2009 virus before its circulation. 19% of persons had anti A (H5N2) IgA before vaccination. Two-fold vaccination with A (H1N1) pdm2009 and A (H5N2) LAIVs resulted in local antibody conversions in 54% and 27% of volunteers, respectively. Both these vaccines increased local IgA avidity. The number of antibody conversions after vaccination with seasonal LAIVs was in inverse dependence on their titers before vaccination. These results make it possible to conclude that the intensity of local antibody immune response to any LAIV depends on the state of local immunological memory, particularly on the presence of the crossreactive antibody-secreting B cells.

[Humoral and cell-mediated immune responses in humans to the A/California/07/ 2009 (H1N1) virus, A(H1N1)pdm2009].

During the twentieth century the world faced four influenza A pandemics: A (H1N1) in 1918, A (H2N2) in 1957, A (H3N2) in 1957 and A (H1N1) recirculation in 1977. In the beginning of 2009 the global spread of A(H1N1)pdm2009 virus was detected. In consideration of clinical evidences and genetic data analysis WHO declared as the novel pandemic of 21th century. However, the fact of exceedingly prolonged previous worldwide circulation of A (H1N1) influenza viruses was not taken into account. Further development showed epidemiological prognosis not to be accurate enough. The present work is an attempt to analyze this question from the immunological standpoint based on our studies of antibody and cellular immunity to A(H1N1)pdm2009 virus in vaccinated and non-vaccinated persons of different ages. The study results allow concluding that A(H1N1)pdm2009 is the drift variant of A (H1N1) viruses antigenically close to A/Swine/1976/1931 (H1N1). It was shown that the significant of persons have cross-reactive B and T cell immunological memory to A(H1N1)pdm2009 strain. This could be a reason of decreased A(H1N1)pdm2009 pandemic severity.

[Stimulation of homo- and heterologic T-cell immunological memory in volunteers inoculated with live influenza A (H5N2) reassortant vaccine].

The study deals with the ability of live attenuated reassortant influenza vaccine (LAIV) A (H5N2) to stimulate a CD4+ and CD8+ immunological memory T cell-mediated immune response in volunteers. These data were compared with the quantitative characteristics of a humoral immune response. A two-dose regimen of intranasal vaccination of avian influenza naïve people with A (H5N2) LAIV induced the production of circulating CD4+ and CD8+ memory cells specific to both A (H5N2) and seasonal A (H1N1) influenza strains. Some of the volunteers were not absolutely A (H5N2) influenza virus naïve since they had been found to have this virus-specific cross-reactive immunological memory T-cells in the prevaccination period. The content (%) of these cells varied significantly within the group. The quantitative values of postvaccination CD4+ and CD8+ memory cell accumulation were inversely related to their prevaccination level.

[Estimation of human and animal immunological memory by testing the trogocytosis of virus-specific T lymphocytes].

This study is the first attempt to evaluate the immunogenicity of Russian live attenuated influenza reassortant influenza vaccine (LAIV), by using a modified T-cell recognition of antigen presenting cells by protein capture (TRAP) method. Single vaccination of 18-20-year-old volunteers with LAIV causes an increase in the peripheral blood levels of virus-specific memory CD4+ T lymphocytes. Some (40-60%) LAIV-vaccination volunteers respond to immunization by showing a significant elevation in the peripheral blood level of memory CD4+ T cells without a systemic humoral immune response recorded in the passive hemagglutination test. Vaccination of mice with live attenuated A (H1N1) influenza reassortant virus stimulates the production of memory CD8+CD44hi T lymphocytes in the nasal-associated lymphoid tissue, the entry of infection, so does influenza infection. Vaccination with inactivated A (H1N1) influenza virus practically fails to induce these cells. A (H1N1) influenza virus-specific CD8+CD44hi T lymphocytes remain within at least 2 months (observation time). The authors' modified TRAP may be used to evaluate virus-specific immunological T-cell memory after vaccination.

Memory T-cell immune response in healthy young adults vaccinated with live attenuated influenza A (H5N2) vaccine.

Cellular immune responses of both CD4 and CD8 memory/effector T cells were evaluated in healthy young adults who received two doses of live attenuated influenza A (H5N2) vaccine. The vaccine was developed by reassortment of nonpathogenic avian A/Duck/Potsdam/1402-6/68 (H5N2) and cold-adapted A/Leningrad/134/17/57 (H2N2) viruses. T-cell responses were measured by standard methods of intracellular cytokine staining of gamma interferon (IFN-γ)-producing cells and a novel T-cell recognition of antigen-presenting cells by protein capture (TRAP) assay based on the trogocytosis phenomenon, namely, plasma membrane exchange between interacting immune cells. TRAP enables the detection of activated trogocytosis-positive T cells after virus stimulation. We showed that two doses of live attenuated influenza A (H5N2) vaccine promoted both CD4 and CD8 T-memory-cell responses in peripheral blood of healthy young subjects in the clinical study. Significant differences in geometric mean titers (GMTs) of influenza A (H5N2)-specific IFN-γ(+) cells were observed at day 42 following the second vaccination, while peak levels of trogocytosis(+) T cells were detected earlier, on the 21st day after the second vaccination. The inverse correlation of baseline levels compared to postvaccine fold changes in GMTs of influenza-specific CD4 and CD8 T cells demonstrated that baseline levels of these specific cells could be considered a predictive factor of vaccine immunogenicity.