The Impact Of Host Genetic And Viral Determinants On The Severity Of Seasonal Influenza Infection In Human

Influenza is a well-known major infectious disease that threatens human health globally.Both seasonal and pandemic influenza are gravely harmful to human being.According to World Health Organization(WHO),influenza epidemic is responsible for 3 to 5 million severe cases and 250,000 to 500,000 deaths each year globally.As the pathogenicity of influenza virus is mainly determined by the interaction of influenza virus and host factors,the clinical severity of influenza virus infections in humans may vary.So far,it has been proved that the pathogenicity of the virus is affected by some amino acid mutations,including those affecting the binding specificity of the surface glycoprotein HA,and the activity of the viral polymerase.In recent years,single nucleotide polymorphisms(SNPs)have been used in studies of the genetic susceptibility of infectious diseases.A great number of genes related to influenza virus infection have been systematically selected through the high-throughput screening platform.In combination with in vitro or bioinformatics analysis,some host gene mutations affecting the pathogenicity of influenza virus have been found.However,the specific mechanism is very complex,and many questions remain unanswered.Continuous surveillance on the seasonal influenza viruses is the basis of the WHO's annual recommendation for influenza vaccine strains.Therefore,the discovery of new amino acid mutations affecting the pathogenicity of influenza viruses is also critical for influenza prevention and control.Although different cytokine and chemokine profiles between clinically mild and severe cases infecting with A(H1N1)pdm09 influenza virus have been studied previously,similar studies on cases infected with A(H3N2)influenza and influenza B virus are still limited.Previous studies have also reported some SNPs associated with A(H1N1)pdm09 influenza infection susceptibility or infection,but whether these SNPs are associated with A(H3N2)or influenza B virus has barely ever been reported.Therefore,the impact of host genetic and viral determinants of the severity of seasonal influenza infection in human was evaluated in this study,through the collection of swabs and blood samples of severe and mild cases of A(H1N1)pdm09.A(H3N2)and B influenza infection.First,this study analyzed the demographics and risk of severity of influenza cases,and found that the risk of developing severe influenza was different among age groups after infection with different subtypes of inluenza virus.For A(H1N1)pdm09 influenza virus infection,cases?60 years age are 6.6 times(95%CI:1.893-23.012)more likely to develop severe outcome than those of 18-59 years age;For those infected with infection A(H3N2)virus and influenza B virus,cases of 0-4 years age are 42.824 times(95%CI:5.217-351.499)and 159.923 times(95%CI:21.059-1214)more likely to develop severe disease than 18-59 age group,respectively.There is no significant difference between male and female infected with different subtypes of influenza viruses.In this study,throat swabs of mild and severe cases infected with A(H1N1)pdm09 influenza virus were subjected to whole genome sequencing using the next generation sequencing(NGS).Base ratio between the two groups were also analyzed to detect amino acid variation.The results showed that ATCG ratio in 141 nucleotide positions of 8 gene fragments was significantly different between mild and severe cases(P<0.05).The bases in 18 nucleotide positions of them can lead to amino acid differences,mainly distributed in HA,M,NA,PA and PB2 gene fragments.The PA gene fragment analysis showed that PA V379I mutations presented in 40.82%mild cases and 20%severe cases,and the difference is significant(P<0.05).In order to investigate whether these amino acid sites are related to the pathogenicity of the virus,PA 379 was first selected to verify the function of PA 379V and 3791 mutations.We found that the mutation of PA V379I can attenuate the virulence of pdmH1N1 virus in mice.The phenomenon in mice model was consistent with the substitution profile of ILI outpatients that possessed a higher proportion of V379I mutation in this study.In this study,the different plasma concentration of 38 subtypes of cytokines/chemokines between mild and severe cases infected with influenza A and B virus was analyzed.The results showed that after infection with A(H1N1)pdm09 virus,disease severity of cases under 18 years old was associated with the decrease in antiviral activity caused by innate immune response reducing,but for cases over 18 years old was associated with with immune pathology due to elevated inflammatory cytokines.The concentration of 5 cytokines/chemokines of severe A(H1N1)pdm09 cases under 18 years old was significantly lower than those of mild cases(P<0.05).For severe pdmH1N1 cases over 18 years old,the level of 6 cytokines/chemokines were significantly higher than those in mild cases(P<0.05).For severe cases infected with A(H3N2)influenza viruses,the level of 4 cytokines/chemokines were significantly lower than those in mild cases(P<0.05).For severe influenza B cases,the concentration of 4 cytokines/chemokines were significantly higher than those of mild cases(P<0.05),and the level of 16 cytokines/chemokines were significantly lower than those of mild cases(P<0.05).The result indicated that disease severity of cases infection with influenza B was associated with reduced innate immune response and immune pathology.In this study,136 SNPs related to 46 genes were compared between Chinese patients with severe and mild cases infected with different subtype influenza virus.We found that the rs2069840-G allele of IL-6 gene might be correlated with severe A(H1N1)pdm09 influenza infection,and the GC genotype has a higher risk of severe infection.The rs3136558-G allele of IL1B gene may be associated with severe A(H1N1)pdm09 influenza infection,and the GA and GG genotypes have a higher risk of severe infection;the rs2856838-A allele of ILIA gene may be associated with severe A(H3N2)influenza infection and AA genotype has a higher risk of severe infection;the rs9622682-AA and rs2899292-GG genotypes of LGALS1 gene are higher risk of A(H3N2)influenza infection.This study also found that IFITM3 rs12252-C allele may be associated with severe influenza B infection,and both CC and CT genotypes have a higher risk of severe infection.In summary,this study found that the risk of developing severe disease of influenza A and B infections is varied among different age groups.People aged?60 years infecting with pdmHIN1 virus showed the highest risk of severe outcome,and children aged 0-4 years are most likely to develop severe disease after infected with H3N2 and influenza B virus.This study found that the V379I mutation of PA protein attenuated the pathogenicity of pdmH1N1 influenza virus in mice for the first time.The plasma concentration of cytokines/chemokines was varied amongst mild and severe cases infected with different subtype of influenza viruses.This study found that IL-6 gene rs2069840-G allele and IL1B gene rs3136558-G allele may be associated with severe A(H1N1)pdm09 influenza infection;the rs2856838-A allele of IL1A gene,the rs9622682-A and rs2899292-G alleles of the LGALS1 gene may be associated with severe A(H3N2)influenza infection;the rsl2252-C allele of IFITM3 was critically associated with severe influenza B infection,and both CC and CT genotypes have a higher risk of severe infection.