The Mx1 gene protects mice against the pandemic 1918 and highly lethal human H5N1 influenza viruses

Mice carrying a wild-type Mx1 gene (Mx1(+/+)) differ from standard laboratory mice (Mx1(-/-)) in being highly resistant to infection with common laboratory strains of influenza A virus. We report that Mx1 also protects mice against the pandemic human 1918 influenza virus and a highly lethal human H5N1 strain from Vietnam. Resistance to H5N1 of Mx1(+/+) but not Mx1(-/-) mice was enhanced if the animals were treated with a single dose of exogenous alpha interferon before infection. Thus, the interferon-induced resistance factor Mx1 represents a key component of the murine innate immune system that mediates protection against epidemic and pandemic influenza viruses.