CCL2 and rheumatoid arthritis: In the case of synovial inflammation in RA, GzmK itself acts as a key inflammatory agent. GzmK induces synovial fibroblasts to activate proinflammatory pathways, including IL-6, CCL2, and ROS production. The protease activity of GzmK can also promote degradation of the ECM, leading to inflammatory cell infiltration and tissue destruction.