CD4 and rheumatoid arthritis: The percolation of autoreactive CD4+ T-cells, plasma cells, and autoantibodies into the synovium initiates the later, destructive phase of RA, characterised by cytokine-driven synovitis and the formation of pannus by the proliferation of fibroblast-like synoviocytes (FLSs), leading to irreversible clinical manifestations [2,3,4,5,6].