Avian influenza could infect and replicate in MSCs.

<p>(<b>A</b>) The ability of avian influenza H5N1 to infect MSCs was compared to human influenza viruses. Cells were infected with H5N1; live or heat-inactivated, H1N1 and H3N2 at an MOI of 10. After 24 h, cells were stained and examined by confocal microscopy for the expression of viral antigens (green) with Evan's blue (red) as a counterstain. The percentages of infected MSCs at high and low MOIs of (<b>B</b>) H5N1 virus and (<b>C</b>) human influenza viruses were determined by flow cytometry. (<b>D</b>) Percent infection of MSCs infected mock, H1N1, H3N2, H5N1, and heat-killed H5N1 at MOI 10 for 24 hours. MDCK infected with H5N1 at MOI 1 for 12 hours was used as a positive control. (<b>E</b>) Real-time PCR of H5N1 M gene in MSCs after infection with H5N1 at various doses for 12 h. The amount of the virus RNA was standardized by beta actin. (<b>F</b>) Production of H5N1 virus from infected MSCs at various time points was measured by plaque assay. The results represent the means and SD of three independent experiments. <i>P</i><0.05 indicates statistically significant differences between H5N1 and human influenza viruses infections.