Abstract: Objective To analysis the genetic evolution characteristics of hemagglutinin (HA) gene of influenza A(H1N1)pdm virus in Changsha City from 2016-2023, to understand the trend of the HA genetic evolution and the mutations of the amino acid. It provides a scientific basis for the prevention and control of influenza epidemics, as well as the screening of vaccines under the new situation. Methods The A(H1N1)pdm09 virus strains from Changsha City from 2016 to 2023 were isolated using SPF chicken embryos, and then the HA genes were sequenced by MiSeq of Illumina Inc. The homology of HA gene was analyzed by MegAlign of the DNASTAR, and the phylogenetic tree was constructed using the Neighbor Joining (NJ) method in the Molecular Evolutionary Genetics Analysis version 11 (MEGA11). Results The homology of the HA gene of A(H1N1)pdm virus in Changsha from 2016 to 2023 was between 94.8%-99.9%, with the HA gene homology decreasing annually. The homology between the isolated strains of A(H1N1)pdm09 in Changsha City from 2016 to 2023 and the WHO recommended vaccine strain ranged from 96.8% to 99.0%, indicating a relatively good match between the flu isolates and the recommended vaccine strain. The phylogenetic tree of the HA gene of the A(H1N1)pdm09 influenza virus in Changsha City showed that the HA gene evolved into several different branches within the 6B branch, and it had currently evolved to 6B.1A.5a.2a branch. Constant mutations had occurred at the amino acid sites of the four antigenic determinant clusters of HA protein. Currently, amino acid mutations had occurred at 15 antigenic sites within the four antigenic determinant clusters, and the newly emerged A186T antigen mutant site in the isolates from 2023 was worth recent notice. The receptor-binding sites are relatively conserved in loop 130, minor amino acid mutations occurred in loop 220, whether the amino acid mutation site in loop 190 is becoming more stable needs to be further monitored. Taking A/California/07/2009 (CY121680) as the reference strain, most of the A(H1N1) pdm09 isolates in Changsha was increased 162 NQTY glycosylation site and was decreased 276 NTTC glycosylation site, and the glycosylation mutations at these two sites have become more stable recently. Conclusions The HA genes of influenza A(H1N1)pdm virus in Changsha are constantly evolving and mutating, suggesting influenza surveillance should be strengthened continuously.

Objective To investigate the immune response to and protective effect of a bivalent DNA vaccine expressing interleukin-2(IL-2)and Gpd proteins in New Zealand rabbits.Methods Seventy-two male New Zealand white rabbits were equally and randomly divided into 4 groups to be immunized with recombinant plasmids pcDNA3.1(+)/Gpd-IL-2(pcD/Gpd-IL-2),pcDNA3.1(+)/Gpd(pcD/Gpd),empty plasmid pcDNA3.1(+)(pcD)and phosphate buffered saline(PBS),respectively.Immunization was carried out by intramuscular injection at multiple sites with a 2-week interval for 3 times.On week 10 after the initial immunization,the rabbits were challenged intradermally with T.pallidum(Nichols strain).Enzyme-linked immunosorbent assay(ELISA)was used to quantify the serum level of anti-Gpd antibodies in the rabbits and the level of IL-2 and interferon(IFN-γ)in the supernatant of Gpd protein-stimulated spleen cells from the rabbits at different time pionts.MTT assay was conducted to detect the proliferation response of spleen cells collected from the rabbits on day 0,14,28,140 and 168 after the challenge.Results Compared with pcD and PBS,both the vaccines pcD/Gpd and pcD/Gpd-IL-2 elicited significantly higher levels of anti-Gpd IgG antibodies in rabbits at different time points during the vaccination and infection period,with the titers peaking at 1 ∶ 1024 and 1∶4096,respectively(both P ＜ 0.01).There were also significant differences in the serum levels of anti-Gpd IgG antibodies between the pcD/Gpd-and pcD/Gpd-IL-2-immunized rabbits at different time points(all P ＜0.01).The levels of IL-2 in the supematant of spleen cells from pcD/Gpd-and pcD/Gpd-IL-2-immunized rabbits on week 8 after the immunization were 110 ± 12.6 and 167 ± 15.7 μg/L respectively,and those of IFN-γwere 225 ± 17.6 and 447 ± 22.4 μg/L respectively,significantly higher than those in that from the other two groups of rabbits(all P ＜ 0.01).Furthermore,an apparent proliferation response was observed in spleen cells from pcD/Gpd-and pcD/Gpd-IL-2-immunized rabbits with a higher stimulation index compared with pcD-and PBS-immunized rabbits(all P ＜ 0.01).Dark-field microscopic examination of early-stage infected lesions revealed that pcD/Gpd-IL-2-immunized rabbits had a lower detection rate(17.5％)of Tp from lesions,occurrence of ulcerative lesions(15％)and shorter curing time compared with pcD/Gpd-immunized rabbits.Conclusion The recombinant plasmid pcDNA3.1(+)/Gpd-IL-2 could induce protective humoral and cellular immune response more efficiently in rabbits.