S100A8 and rheumatoid arthritis: Increased serum levels of S100A8/A9 in SLE, as well as in other connective tissue diseases such as rheumatoid arthritis and Sjogren's syndrome, was first described in 1990 by Kuruto et al. [42] and was later confirmed in SLE both in serum and by a proteomic-based study on PBMCs [33,34,43].