Toll-like receptor 7 is required for effective adaptive immune responses that prevent persistent virus infection.

TLR7 is an innate signaling receptor that recognizes single-stranded viral RNA and is activated by viruses that cause persistent infections. We show that TLR7 signaling dictates either clearance or establishment of life-long chronic infection by lymphocytic choriomeningitis virus (LCMV) Cl 13 but does not affect clearance of the acute LCMV Armstrong 53b strain. TLR7−/− mice infected with LCMV Cl 13 remained viremic throughout life from defects in the adaptive antiviral immune response—notably, diminished T cell function, exacerbated T cell exhaustion, decreased plasma cell maturation, and negligible antiviral antibody production. Adoptive transfer of TLR7+/+ LCMV immune memory cells that enhanced clearance of persistent LCMV Cl 13 infection in TLR7+/+ mice failed to purge LCMV Cl 13 infection in TLR7−/− mice, demonstrating that a TLR7-deficient environment renders antiviral responses ineffective. Therefore, methods that promote TLR7 signaling are promising treatment strategies for chronic viral infections.