Pathogenesis of Hong Kong H5N1 influenza virus NS gene reassortants in mice: the role of cytokines and B- and T-cell responses

J Gen Virol. 2005 Apr;86(Pt 4):1121-1130. doi: 10.1099/vir.0.80663-0.


The severity of disease caused in humans by H5N1 influenza viruses remains unexplained. The NS gene of Hong Kong H5N1/97 viruses was shown to contribute to high pathogenicity of reassortants in a pig model. However, the molecular pathogenesis and host immune response underlying this phenomenon remain unclear. Here, in a mouse model, H1N1 A/Puerto Rico/8/34 (PR/8) reassortants that contained the H5N1/97 NS gene, the H5N1/01 NS gene, or an altered H5N1/97 NS gene encoding a Glu92-->Asp substitution in NS1 was studied. The pathogenicity of reassortant viruses, the induction of cytokines and chemokine CXCL1 (KC) in the lungs and specific B- and T-cell responses was characterized. In mice infected with reassortant virus containing the H5N1/97 NS gene, the mouse lethal dose (50%) and lung virus titres were similar to those of PR/8, which is highly pathogenic to mice. This reassortant virus required two more days than PR/8 to be cleared from the lungs of infected mice. Reassortants containing the altered H5N1/97 NS gene or the H5N1/01 NS gene demonstrated attenuated pathogenicity and lower lung titres in mice. Specific B- and T-cell responses were consistent with viral pathogenicity and did not explain the delayed clearance of the H5N1/97 NS reassortant. The reassortant induced elevated pulmonary concentrations of the inflammatory cytokines IL1alpha, IL1beta, IL6, IFN-gamma and chemokine KC, and decreased concentrations of the anti-inflammatory cytokine IL10. This cytokine imbalance is reminiscent of the clinical findings in two humans who died of H5N1/97 infection and may explain the unusual severity of the disease.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • B-Lymphocytes / immunology*
  • Cytokines / biosynthesis*
  • Disease Models, Animal
  • Female
  • Humans
  • Influenza A Virus, H5N1 Subtype*
  • Influenza A virus / genetics
  • Influenza A virus / pathogenicity*
  • Influenza, Human / immunology
  • Influenza, Human / physiopathology
  • Influenza, Human / virology
  • Lung / immunology
  • Lung / physiopathology
  • Lung / virology
  • Mice
  • Mice, Inbred BALB C
  • Reassortant Viruses / genetics
  • Reassortant Viruses / pathogenicity*
  • T-Lymphocytes / immunology*
  • Viral Nonstructural Proteins / genetics
  • Viral Nonstructural Proteins / immunology*
  • Virulence


  • Cytokines
  • Viral Nonstructural Proteins