Pattern of mutation in the genome of influenza A virus on adaptation to increased virulence in the mouse lung: Identification of functional themes

Abstract

The genetic basis for virulence in influenza virus is largely unknown. To explore the mutational basis for increased virulence in the lung, the H3N2 prototype clinical isolate, A͞HK͞1͞68, was adapted to the mouse. Genomic sequencing provided the first demonstration, to our knowledge, that a group of 11 mutations can convert an avirulent virus to a virulent variant that can kill at a minimal dose. Thirteen of the 14 amino acid substitutions (93%) detected among clonal isolates were likely instrumental in adaptation because of their positive selection, location in functional regions, and͞or independent occurrence in other virulent influenza viruses. Mutations in virulent variants repeatedly involved nuclear localization signals and sites of protein and RNA interaction, implicating them as novel modulators of virulence. Mouse-adapted variants with the same hemagglutinin mutations possessed different pH optima of fusion, indicating that fusion activity of hemagglutinin can be modulated by other viral genes. Experimental adaptation resulted in the selection of three mutations that were in common with the virulent human H5N1 isolate A͞HK͞ 156͞97 and that may be instrumental in its extreme virulence. Analysis of viral adaptation by serial passage appears to provide the identification of biologically relevant mutations.

Immunization with live nonpathogenic H5N3 duck influenza virus protects chickens against highly pathogenic H5N1 virus

“…We speculate that the high pH optimum of HA-mediated fusion can be responsible for the pathogenicity of this virus. Dependence of replication efficiency and pathogenicity of influenza viruses on fusion pH was well documented previously (Brown et al, 2001;Hsu et al, 2006;Reed et al, 2010;Shelton et al, 2013).…”

Critical Negative Regulation of Type 1 T Cell Immunity and Immunopathology by Signaling Adaptor DAP12 during Intracellular Infection

“…Pulmonary influenza infection was elicited by intranasally infecting mice with 1 ϫ 10 5 PFU of a mouse-adapted human influenza A virus (31). At different times, flu Ag-specific CD8 T cell responses were analyzed with the cells obtained from the lung, spleen, and lymph nodes by flu nuclear protein (NP) tetramer immunostaining without culture or by IFN-␥ intracellular cytokine staining (ICCS) upon culture with NP peptides.…”

Characterization of the 1918 “Spanish” Influenza Virus Matrix Gene Segment

“…The matrix segment has been shown in several experimental systems to have a significant effect on virulence and viral replication rate (6,13,43,44,51,55). In some of these studies, matrix proteins differing by as little as 1 or 2 amino acids conferred striking differences in phenotype.…”