TNF and inflammation: Besides the IL-23/IL-17 axis, we have now also demonstrated this for TNF: whereas the soluble form of TNF, signaling exclusively through the TNF-R1, drives profound synovitis and bone destruction reminiscent of what we observe in human RA, the transmembrane form of the same cytokine drives osteoproliferative axial and peripheral joint inflammation as seen in SpA (23).