Together, these data may provide one explanation for the fact that rituximab treatment, similar to TNF blockade, does not induce complete remission in the majority of the RA patients and suggest that blocking the PGE2 pathway by targeting MPGES1 may lead to novel therapeutical strategies and complement current anti-rheumatic therapy by providing additional benefit in controlling the inflammatory process in the rheumatoid joint. Here, TNF is linked to rheumatoid arthritis.