IFITM3 and influenza: Mice lacking a functional Ifitm3 gene developed severe viral pneumonia when challenged with normally low pathogenic viruses, and protection was re-established with reintroduction of Ifitm3. In humans, an overrepresentation of individuals with the IFITM3 rs12252 variant (C allele) that alters a splice acceptor site was found in European patients who required hospitalization as a result of influenza infection [11].