The patients enrolled in this study were divided into two groups: diabetic and non diabetic patients. The diabetic patients were characterized by significantly higher levels of fasting serum glucose as well as of hemoglobin A1C. Serum lipid profile, concomitant diseases and drug therapy (besides hypoglycemic therapy) were similar in both group of patients, therefore changes in carotid lesion from diabetic patients could be related to additional factors beside hypercholesterolemia, hypertension or differences in drug therapy.
CRP content as well as IL-6 levels were significant higher in carotid lesions from diabetic patients in comparison to non-diabetic patients. These results clearly illustrate the higher inflammatory content of atherosclerotic lesions from diabetic patients. These results are compatible with previous studies showing higher inflammatory characteristics in vascular cells and in coronary plaques from diabetic patients [23, 24], illustrated by higher levels of cytokines, TNFα, adhesion molecules and chemo attractant factors release in diabetic patients in comparison to non-diabetic patients.
CRP content in the carotid lesion could be produced by arterial macrophages since CRP staining in the lesions co-localized with CD68, a specific staining for macrophages as previously shown [15, 25]. CRP locally produced could be responsible for the higher levels of IL-6 measured in carotid lesions from diabetic patients or inversely, since CRP was both shown to be regulated by dual action of IL1 and IL6 and shown to induce IL-6 synthesis and release from cells of the atherosclerotic lesion .
These results are compatible with previous studies showing both CRP mRNA and protein localized in atherosclerotic lesions, predominantly in vascular smooth muscle cells and macrophages . Supporting this hypothesis, inflammatory stimuli such as TNFα or combination of IL1/IL6 have been found to induce CRP-production from human coronary artery cells .
CRP content and mRNA expression as well as IL6 content were determined in human monocytes derived macrophages. No significant differences in these parameters could be detected between diabetic and non diabetic patients. However, when plotting CRP carotid artery content against CRP HMDM content or against CRP mRNA expression in HMDM, a significant positive correlation was obtained. These results illustrate that since HMDM and arterial macrophages differentiate from a common monocytic cellular lineage, HMDM could reflect and undergo similar regulation to that observed in arterial lesion. It has been previously shown that monocytes will differentiate into specific macrophage subpopulations (similar to that located in tissues) in response to alternative cytokine environments . Moreover, circulating monocytes of patients with cardiovascular disease have been shown to display high levels of surface receptors that may be involved in inflammatory responses . If indeed carotid plaques CRP correlates with HMDM CRP, providing that atherosclerotic lesion cannot be easily obtained for diagnostic purposes, HMDM obtained from blood samples could be easily available, to assess atherosclerotic lesion inflammatory status.
CRP produced by macrophages, unlike systemic hepatocyte-derived CRP, could be selectively up-regulated following pro-atherosclerotic factors. Although we expect macrophage CRP levels to be significantly lower than systemic hepatocyte-derived CRP, these levels are expected to be specific to atherosclerotic development and not influenced by general systemic inflammatory processes that usually lead to massive increase in serum CRP, a positive acute phase reactant. This was further illustrated by the highly heterogeneous blood CRP levels in diabetic patients observed in this study.
These results could also shed some light on the controversy of whether serum CRP is indeed a biomarker for cardiovascular diseases and whether it is a pro-atherogenic factor [31, 32]. If, CRP is produced from different sources  (including blood monocytes derived macrophages) and if as we hypothesize, CRP regulation is cell specific, this could lead to an heterogeneous population of CRP molecules. CRP locally produced in the atherosclerotic lesion could be structurally different from circulating CRP, including dissociation into monomers instead of the pentameric structure of hepatocyte-produced CRP [33–35].Therefore by referring only to systemic CRP, we are losing precious information on CRP from additional sources and this could explain discrepancies between studies on CRP casual involvement in cardiovascular diseases.
We conclude that pro-inflammatory effects mediated by CRP in the arterial wall could be caused by locally secreted macrophage CRP and that measurement of CRP in blood-derived macrophages could reflect atherosclerotic macrophages secretion of CRP. Further studies are needed however to investigate the correlation between levels of CRP produced by arterial macrophages, and the prediction of coronary artery disease. Understanding of locally produced macrophage CRP in the arterial wall during atherogenesis could be of major importance in our understanding of the mechanisms underlying inflammatory response pathways during atherogenesis.