Soluble IL-15 has been detected in synovia of patients with RA mainly expressed by macrophages, fibroblasts, and endothelial cells [13, 14], and there it recruits circulating memory T cells in the synovial membrane and may up regulate TNFα, IL-17, and other proinflammatory cytokines [15–17]. Here, IL15 is linked to rheumatoid arthritis.