A glimpse on the phenomenon of macrophage polarization during atherosclerosis

Atherosclerosis and associated cardiovascular disease are the leading causes of mortality in developed countries and the World Health Organization has estimated that by 2020 these disorders will be the main sanitary and socio-economic problem world-wide due in part to the progressive aging of our societies. Atherosclerosis is a complex chronic inflammatory process triggered and perpetuated by cardiovascular risk factors which cause endothelial dysfunction and leukocyte infiltration within the subendothelial space in the artery wall. In this review, we summarize the mechanisms that govern the recruitment of circulating monocytes into the incipient atherosclerotic lesion and their differentiation into macrophages. Moreover, we discuss current knowledge on macrophage polarization, a phenomenon of increasing interest given recent work suggesting that different stages in the progression of atherosclerosis are associated with the presence of distinct macrophage subtypes. Understanding the molecular mechanisms that orchestrate macrophage polarization and the precise role of distinct macrophage subsets should provide a basis for novel treatment strategies to limit the progression of atherosclerosis.