Another highly up-regulated gene, CHI3L1 (2,409 fold) or cartilage glycoprotein-39, a catalytically inactive member of glycohydrolase family 18, is a 39-kDa glycoprotein secreted by articular chondrocytes [22], synoviocytes [23], and macrophages [24] and its expression has been linked to both rheumatoid arthritis and osteoarthritis [25]. Here, CHI3L1 is linked to rheumatoid arthritis.