Although it is not fully elucidated, the TLR-interleukin axis is likely to be involved in the process of joint inflammation and cartilage degeneration induced by carrageenan, since synovial cells also express both TLR2 and TLR4 and their expression levels are increased in RA (rheumatoid arthritis) synovium [32]. Here, TLR2 is linked to inflammation.