ALOX15 and rheumatoid arthritis: Studies show that 5-LOX and 15-LOX are primarily existing in the synovium of RA and OA, and therein 15-LOX is a lipid-per oxidizing enzyme that predominantly expressed in eosinophils, macrophages, fibroblasts and most articular tissues, including cartilage, synovium, and bone and its products are found in human synovial fluids, while 5-LOX is mainly located in the lining/sublining macrophages, neutrophils, and mast cells (Colamorea et al., 1999; Klein et al., 2004).