C-reactive protein: history and revival.

C-reactive protein (CRP) is the prototype acute-phase protein, which can increase up to 1000-fold after the onset of a stimulus. Aside from its disputed role as a marker of infection and/or inflammation in daily clinical practice, the protein has a wide variety of biological properties and functions. Due to its opsonizing abilities and its capability to activate human complement, CRP plays an important role in the innate host defense against different microorganisms, such as bacteria and fungi. The same opsonophagocyting properties can lead to clearance of host cell material, including nuclear constituents. Inflammation is one of the cornerstones in the etiology and pathogenesis of atherosclerosis, which led to worldwide attention being focused on CRP and its role in the process of atherosclerosis. This role may have a dual character. First, CRP levels reflect the 'burden' of inflammation within atherosclerotic lesions, thus reflecting the grade of vulnerability and instability of the plaques. For this reason, an increased level of the protein may be a prelude to rupture of the plaque and, thus, to occlusive arterial disease. Secondly, CRP may play an active role in the atherosclerotic process. CRP plays a role in the expression of different adhesion molecules on endothelial cells and the protein is able to activate human complement within the plaque. Furthermore, the recent discovery of local production of CRP and complement proteins within the plaque suggests an active role for the protein in the inflammatory cascade. Whatever the role for CRP in the atherosclerotic process, it has been proven that an elevated CRP level, with a cut-off point of approximately 3 mg/l, is associated with an increased risk of occlusive arterial disease, especially acute coronary syndromes.