IL17A and arthritic joint disease: IL-17A is involved in arthritis in several mechanisms: it is able to promote the synthesis of matrix metalloproteinases (MMP) 1, 9 and 13 which can lead to degradation of the extracellular matrix in the joint; increases the expression of the receptor NFKB ligand – RANKL by osteoblasts which leads to the activation of osteoclasts and bone degradation; lastly, IL-17A stimulates angiogenesis followed by increased blood flow and influx of inflammatory cells to the joint.