It therefore appears that (1) all vaccinia-infected cells are blocked in their ability to produce type-I IFN directly (even though both NHBEs and A2780 can produce type-I IFN in response to infection with the related MV); (2) C33A is unable to produce IFN in response to TLR activation; and (3) A2780 cells are unable to respond directly to type-I IFN. This evidence concerns the gene IFNA1 and infection.