Protection against IAV infection is also provided by the humoral immune response. To test whether loss of A20 in myeloid cells affects B cell mediated immunity, we determined hemagglutinin (HA) antibody titers in the serum of A20myel-KO and wild type littermates. However, no differences could be detected between wild type and A20myel-KO animals (figure S2D), indicating that humoral immunity is not affected by A20 expression in myeloid cells. Together, these data suggest that mechanisms other than adaptive immunity, such as an increased innate immune response, characterized by an increased influx of neutrophils and increased numbers of alveolar macrophages, contribute to the better viral clearance in A20myel-KO mice.