In plasmacytoid DCs, the production of type 1 interferons (IFN) is enhanced in response to viral or exogenous nucleic acids via TLR7 and TLR9 (Seillet et al., 2012), whereas progesterone downregulates TLR9-mediated IFN-α production in response to viral infections potentially increasing a woman's risk for HIV and herpes simplex virus (HSV) (Hughes et al., 2008). This evidence concerns the gene TLR9 and viral infectious disease.