TLR9 and viral infectious disease: In the battle with viral infections, TLR3 and TLR10 recognize double-stranded RNA (dsRNA; Lee et al., 2018; Wei and Lan, 2018), whereas TLR7, TLR8, and TLR9 make up the TLR7 family, with TLR7 and TLR8 detecting single-stranded RNA (ssRNA) and TLR9 recognizing unmethylated CpG DNA (Kawai and Akira, 2011).