Toll-like receptor 7, also known as TLR7, is a protein that in humans is encoded by the TLR7 gene. Orthologs are found in mammals and birds. It is a member of the toll-like receptor (TLR) family and detects single stranded RNA. The TLR family plays an important role in pathogen recognition and activation of innate immunity. TLRs are highly conserved from Drosophila to humans and share structural and functional similarities. They recognize pathogen-associated molecular patterns (PAMPs) that are expressed on infectious agents, and mediate the production of cytokines necessary for the development of effective immunity. The various TLRs exhibit different patterns of expression. This gene is predominantly expressed in lung, placenta, and spleen, and lies in close proximity to another family member, TLR8, on the human X chromosome. TLR7 recognizes single-stranded RNA in endosomes, which is a common feature of viral genomes which are internalised by macrophages and dendritic cells. TLR7 recognizes single-stranded RNA of viruses such as HIV and HCV. TLR7 can recognize GU-rich single-stranded RNA. However, the presence of GU-rich sequences in the single-stranded RNA is not sufficient to stimulate TLR7.