IFITM3 and infection: The well-defined ability of IFITM3 to prevent infection of cells by influenza virus, along with the increased virus-induced morbidity and mortality of IFITM3 KO mice, has prompted numerous research groups to examine whether single nucleotide polymorphisms (SNPs) in the human IFITM3 gene associate with influenza virus infections or infection severity (all studies to date are summarized in Table 2).