IFNL1 and rheumatoid arthritis: Many investigators have demonstrated that IL-29 plays an important role in the pathogenesis of many types of autoimmune and inflammatory diseases, such as systemic sclerosis, rheumatoid arthritis and systemic lupus erythematosus.5, 6, 7 However, the association of IL-29 with Psoriasis Vulgaris (PV) is still poorly understood.