In a research study conducted both in vivo and in vitro, Ronan Le Goffic et al. evaluated both the expression of IL-33 in H1N1 influenza A virus–induced pulmonary infection in mice after 3 days from infection and the induction of IL-33 in response to infections with different strains of the same virus in cultured human and murine epithelial cells. This evidence concerns the gene IL33 and infection.