Molecular basis of replication of duck H5N1 influenza viruses in a mammalian mouse model - PubMed (original) (raw)

Molecular basis of replication of duck H5N1 influenza viruses in a mammalian mouse model

Zejun Li et al. J Virol. 2005 Sep.

Abstract

We recently analyzed a series of H5N1 viruses isolated from healthy ducks in southern China since 1999 and found that these viruses had progressively acquired the ability to replicate and cause disease in mice. In the present study, we explored the genetic basis of this change in host range by comparing two of the viruses that are genetically similar but differ in their ability to infect mice and have different pathogenicity in mice. A/duck/Guangxi/22/2001 (DKGX/22) is nonpathogenic in mice, whereas A/duck/Guangxi/35/2001 (DKGX/35) is highly pathogenic. We used reverse genetics to create a series of single-gene recombinants that contained one gene from DKGX/22 and the remaining seven gene segments from DKGX/35. We find that the PA, NA, and NS genes of DKGX/22 could attenuate DKGX/35 virus to some extent, but PB2 of DKGX/22 virus attenuated the DKGX/35 virus dramatically, and an Asn-to-Asp substitution at position 701 of PB2 plays a key role in this function. Conversely, of the recombinant viruses in the DKGX/22 background, only the one that contains the PB2 gene of DKGX/35 was able to replicate in mice. A single amino acid substitution (Asp to Asn) at position 701 of PB2 enabled DKGX/22 to infect and become lethal for mice. These results demonstrate that amino acid Asn 701 of PB2 is one of the important determinants for this avian influenza virus to cross the host species barrier and infect mice, though the replication and lethality of H5N1 influenza viruses involve multiple genes and may result from a constellation of genes. Our findings may help to explain the expansion of the host range and lethality of the H5N1 influenza viruses to humans.

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Figures

FIG. 1.

FIG. 1.

Replication and virulence of rescued viruses. Colored bars indicate the origin of the viral gene: blue, A/duck/Guangxi/22/01 (DKGX/22); red, A/duck/Guangxi/35/01 (DKGX/35). The red dots in the mouse figures indicate tissue tropism (upper left, brain; lower left, lung; upper right, kidney; lower right, spleen). The MLD50 was determined by inoculating groups of five mice with 10-fold serial dilutions containing 101 to 106 EID50 of the virus in a 50-μl volume (4) and calculated by the method of Reed and Muench (20). The MLD50 values of DKGX/35 and R-DKGX/35 are the means of three experiments, and the values of other viruses were obtained from a single experiment.

FIG. 2.

FIG. 2.

PB2 mutant viruses and their virulence in mice. Colors indicate the origin of the gene, gene region, or encoded amino acid: blue, DKGX/22; red, DKGX/35. The amino acid differences between DKGX/22 and DKGX/35 PB2 are shown as single letters with the positions numbered at the top. The red dots in the mouse figures indicate tissue tropism (upper left, brain; lower left, lung; upper right, kidney; lower right, spleen). The MLD50 was determined by inoculating groups of five mice with 10-fold serial dilutions contain 101 to 106 EID50 of the virus in a 50-μl volume (4) and calculated by the method of Reed and Muench (20). The MLD50 value of R-DKGX/35 is the mean of three experiments, and the values of other viruses were obtained from single experiment. Amino acid abbreviations: T, Thr; A, Ala; N, Asn; D, Asp; K, Lys.

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