S100A8 and rheumatoid arthritis: It has been shown that S100A8/A9 can be a useful biomarker of activity of disease or predictor of severity of disease in various rheumatic diseases, such as juvenile idiopathic arthritis (JIA), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), anti-neutrophil cytoplasmic antibodies-associated vasculitis (AAV), lung fibrosis in systemic sclerosis, adult-onset Still’s disease, Kawasaki disease (KD), or autoinflammatory diseases [4,7,8,9,10,11,12].