MMP9 and silicosis: One study conducted in China by Jiang et al.29 evaluated plasma levels of TNF-α and matrixmetalloproteinase-9 (MMP-9) in exposed groups with and without silicosis as well asin healthy controls and found increased levels in both exposed groups (with andwithout silicosis), although they were highest in patients with silicosis.TNF-α is an important cytokine initiator of inflammatory responses, andseveral studies show its production is increased in mononuclear cells from patientswith silicosis.