IFNA1 and infection: C33-A cells were pretreated with increasing concentrations of IFN-λ1, IFN-λ2 (0, 10, 20, 30 and 40 ng/ml) or IFN-α (0, 100, 200, 300 and 400 IU/ml) prior to infection with DENV-2 (MOI = 0.1).