Meanwhile, a variety of endogenous TLR ligands, including heat shock proteins, high mobility group box-1 protein (HMGB1), host DNA, fibrinogen, and tenascin-C, have been identified in the synovium of patients with RA, predominantly TLR2 and/or TLR4 agonists [55, 56]. Here, TLR2 is linked to rheumatoid arthritis.