TLR4 and rheumatoid arthritis: Accumulating evidence has shown that TLR4, which expressed in various T cell subsets, including CD4+ T cells, CD8+ T cells, Tregs and natural killer (NK) T cells [28], is an important contributor to the development of multiple autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) [29], and experimental autoimmune encephalomyelitis (EAE).