S100A9 and inflammatory response: Calprotectin (also known as the S100 proteins, S100A8/S100A9 [6], MRP8/MRP14 [4], calgranulin A and B [7], and L1 protein [8]) is a major leukocyte cytosolic protein released locally during inflammatory processes predominantly by activated leukocytes at the site of joint inflammation and thus directly reflects joint inflammatory activity rather than systemic inflammation [9].