IL4 and viral infectious disease: Bite-associated enhancement of infection was apparent in severe combined immunodeficiency (SCID) mice, which lack T and B cells (Figure 3A), whereas classic Th1 or Th2 cytokines (e.g., IFN-γ, IL-4) could not be detected after mosquito biting of naive wild-type mice in the absence of virus infection (Figure S2).