High level of genetic compatibility between swine-origin H1N1 and highly pathogenic avian H5N1 influenza viruses

Abstract

Reassortment is an important mechanism for the evolution of influenza viruses. Here, we coinfected cultured cells with the pandemic swine-origin influenza virus (S-OIV) and a contemporary H5N1 virus and found that these two viruses have high genetic compatibility. Studies of human lung cell lines indicated that some reassortants had better growth kinetics than their parental viruses. We conclude that reassortment between these two viruses can occur and could create pandemic H5N1 viruses.

FIG. 1.

Viral growth of reassortants in A549-M2 cells. Cells were infected with M2-knockout viruses, produced by reverse genetics, representing all of the possible RNP gene combinations between CA04 and VN31604, with all of the remaining genes (HA, NA, M, and NS) derived from VN31604, at an MOI of 0.0005. RNP complex gene segments derived from CA04 and VN31604 are shown in gray-shaded and clear boxes, respectively. Virus yields at the indicated time points were determined by plaque assay in M2CK cells. Data represent the means of results of three independent infections ± standard deviations.

FIG. 2.

Viral growth of reassortants in NCI-H358-M2 cells. Cells were infected with M2-knockout viruses, produced by reverse genetics, containing the indicated RNP gene combinations between CA04 and VN31604, with all of the remaining genes (HA, NA, M, and NS) derived from VN31604, at an MOI of 0.001. RNP complex gene segments derived from CA04 and VN31604 are shown in gray-shaded and clear boxes, respectively. Virus yields at the indicated time points were determined by plaque assay in M2CK cells. Data represent the means of results of three independent infections ± standard deviations.

FIG. 3.

Polymerase activities of 16 RNP gene combinations measured in a minigenome assay. Four expression plasmids (PB2, PB1, PA, and NP) for the 16 RNP gene combinations between CA04 and VN31604, together with pPolINP(0)luc2(0) for the production of virus-like RNA encoding the reporter luciferase gene, were transfected into 293 cells and assayed for luciferase activity after 24 h of incubation at 37°C. The values shown are means ± standard deviations for results of three independent experiments and are standardized to the activities of the expression plasmids for the VN31604 RNP complex proteins (100%). Genes derived from CA04 and VN31604 are shown in gray-shaded and clear boxes, respectively.