TLR7 and Arthritis: Finally, a recent study showed that both TLR3 KO and TLR7 KO mice developed reduced K/BxN serum-induced arthritis (74) and that the transcription factor, interferon regulatory factor 5 (IRF5), contributed to disease progression by mediating pro-inflammatory cytokine production, mainly that of IL-1β generated downstream of TLR3 and TLR7 (74).