MX1 and infection: Although the amount of IFN-λ detected in GRW/Aa stock was barely detectable, we wanted to distinguish whether the MxA induction observed after GRW/Aa infection of A549 cells (Figure 3) was caused just by passively transferred IFN-λ present in the virus stock or by de novo produced IFN induced by GRW/Aa virus infection (Figure 4B).