In viral infection, both host cell membrane-localized TLRs (TLR2, TLR4, detecting viral envelope proteins) and endosomal TLRs (TLR3, TLR7, TLR8, and TLR9, nucleic acid sensors) initiate signal transduction cascades leading to IFN production (Figure 1). The gene discussed is TLR9; the disease is viral infectious disease.