TLR4 and rheumatoid arthritis: Celastrol markedly inhibited the LPS-induced phosphorylation of IκBα, TLR4 and MyD88 expression, but celastrol did not inhibit the expression of TRIF, suggesting celastrol inhibits LPS-induced MMP-9 activation by suppressing TLR4/MyD88/NF-κB pathway in RA-FLSs.