PROS1 and osteoarthritis: CatB is a protease which is believed to have an important role in the degradation of cartilage ECM proteins, such as aggrecan and collagen.(10,12,18) Enhanced expression of CatB has been reported in chondrocytes of osteoarthritis patients.(19) In addition, intervertebral degenerated cells has been believed to be responsible of secretion pro-inflammatory cytokines, including IL-6.(20) The persistent proinflammatory activity of IL-6 favors mononuclear cell accumulation at the site of injury, angio-proliferation and antiapoptotic functions of T cells.(21-23)