TNF and rheumatoid arthritis: This prompted the question of “Why TTP is not acting to reduce TNFα expression in rheumatoid synovial macrophages”.30 A likely answer is that aberrant activation of MAPK p38 in the RA synovium leads to the accumulation of TTP in a phosphorylated and inactive form, so that it is incapable of downregulating TNFα and other targets.