A causal role of C-reactive protein (CRP) in inflammation: Conformational rearrangement in C-reactive protein is required for enhanced pro-inflammatory leukocyte activation and leukocyte adhesion in ischemiareperfusion of the striated muscle

Abstract

C-reactive protein (CRP) is the prototypic acute phase reactant and consists of 5 identical non-covalently linked subunits. Recently it has been proposed that CRP is not only a marker, but also a mediator of inflammatory processes. Here we investigated the pathogenetic role of CRP in ischemiareperfusion and the influence of the conformational change from pentameric CRP (pCRP) to its individual subunits (monomeric CRP:mCRP) on the pro-inflammatory effects of CRP.We examined ischemically challenged and reperfused tissue of the free muscle flap immunohistologically. We also evaluated the impact of native, pentameric CRP and mCRP on the activation of the monocyte integrin Mac-1 (CD11b/CD18), a key regulator of monocyte adhesion to endothelial cells in the microcirculation of inflamed tissues. We further investigated the effect of different CRP isoforms on monocyte adhesion to fibrinogen under static and to adherent platelets and human endothelial cells under shear flow conditions. Specific blockers were used to assess the signal transduction pathways involved in mediating pro-inflammatory CRP effects.We are able to detect mCRP, but not pCRP deposition in reperfused, inflamed muscle tissue after free tissue transfer. In vitro, low concentrations of mCRP(5 μg/ml)lead to significantly increased monocyte adhesion to fibrinogen, platelets and human endothelial cells under shearflow conditions via Mac-1 activation through signal-transduction pathways involving PI3- and Src-kinases. pCRP does not exert pro-inflammatory properties in physiological concentrations in these assays.In conclusion, these results suggest that the loss of pentameric symmetry in CRP, resulting in formation of mCRP, enhances its pro-inflammatory properties. The deposition of mCRP in ischemiareperfusion injury suggests a causal role in the pro-inflammatory pathology of ischemia-reperfusion and associated microcirculatory alterations. Furthermore, our results might explain previously published opposing results regarding the pro-inflammatory properties of CRP and identify mCRP as a potential therapeutic target in inflammatory diseases.