While the actual cause of RA is not known, different environmental and genetic factors are known to initiate activation of T cells, which contribute to RA by stimulating monocytes, macrophages, and synovial fibroblasts, leading to the production of cytokines such as interleukin-1 (IL-1) and Tumor Necrosis Factor α (TNF-α). Here, TNF is linked to rheumatoid arthritis.