IL6 and rheumatoid arthritis: In fact, overproduction of IL-6 in vivo has been shown to cause various clinical symptoms and abnormalities (e.g., spiking fever, skin rash, arthritis, pericarditis, hepatosplenomegaly, and growth retardation) in laboratory models, which may explain the manifestations observed in patients with various inflammatory diseases, including rheumatoid arthritis (RA) and systematic-onset juvenile idiopathic arthritis (soJIA) [23, 24].