TLR9 and viral infectious disease: To better investigate whether the phenomenon described above is applicable also to exogenous nucleic acids, that may mimic the response to viral infection, we exposed cells to the synthetic DNA molecule CpG ODN and polyinosinic:polycytidylic acid (poly I:C), a synthetic analog of the double-stranded RNA, considered as “natural” stimulants of TLR9 and TLR3, respectively [25, 26].