C-Reactive Protein Increases Oxygen Radical Generation by Neutrophils

Abstract

C-reactive protein (CRP) has been suggested to play a role in the pathogenesis of atherosclerosis. Neutrophil respiratory burst and levels of CRP are increased during infection. The increase in the neutrophil respiratory burst may be due to factors that are elevated in infection, such as cytokines, tumor necrosis factor, platelet-activating factor, and CRP. The direct effect of CRP on the release of oxygen radicals by neutrophils is not known. This investigation was made to determine if CRP affects the generation of oxygen radicals by neutrophils and if this effect is blocked by antioxidants. The effect of various concentrations (1 to 200 µg/mL blood) of CRP on the generation of oxygen radicals by neutrophils was measured as luminol-dependent chemiluminescence (chemiluminescent activity) on a luminometer (Auto Lumat LB953, EG & G Berthold, Gaithersburg, MD). The unit of chemiluminescent activity is the relative light unit and was expressed as relative light unit/white blood cell (RLU/WBC). Chemiluminescent activity of blood without CRP was slightly higher than that of buffer with or without CRP. CRP markedly increased the chemiluminescent activity of blood. There was no significant change in the chemiluminescent activity of WBCs with 1 µg/mL of CRP. The chemiluminescent activity increased significantly with higher concentrations of CRP. The percent increases in the chemiluminescent activity with 2, 5, 10, 25, 50, 100 and 200 µg/mL of CRP were 45%, 72%, 50%, 70%, 52%, 67%, and 68% respectively. Antioxidants (superoxide dismutase, catalase, and dimethylthiourea) blocked CRP-induced oxygen radicals by WBCs. These results suggest that CRP increases the generation of oxygen radicals from the WBCs. CRP-induced atherosclerosis may be mediated through generation of oxygen radicals by neutrophils.