TLR4 and rheumatoid arthritis: TLR2, TLR3, TLR4, TLR-5, and TLR9 have been found on FLSs isolated from OA and RA patients (Hu et al., 2014; Iqbal et al., 2016), where the TLR receptor—ligand interaction was shown to induce IL-6, IL-8, TNF-α, and VEGF (Hu et al., 2014).