Lp-PLA2, or lipoprotein-associated phospholipase-A2, measures disease activity within the artery wall below the collagen or calcified cap due to the activation of macrophages. Lp-PLA2 is not an acute phase reactant. When disease is active in the artery, increased levels of Lp-PLA2 are produced by macrophages and foam cells within the intima of the artery. Lp-PLA2 also interacts with oxidized LDL, which increases inflammation and enhances a proatherogenic state, as well as plaque vulnerability. Research suggests that it plays a direct role in the atherosclerotic disease process.