Monocytes in coronary artery disease and atherosclerosis: where are we now?

Despite improvements in interventional and pharmacological therapy of atherosclerotic disease, it is still the leading cause of death in the developed world. Hence, there is a need for further development of effective therapeutic approaches. This requires better understanding of the molecular mechanisms and pathophysiology of the disease. Atherosclerosis has long been identified as having an inflammatory component contributing to its pathogenesis, whereas the available therapy primarily targets hyperlipidemia and prevention of thrombosis. Notwithstanding a pleotropic anti-inflammatory effect to some therapies, such as acetyl salicylic acid and the statins, none of the currently approved medicines for management of either stable or complicated atherosclerosis has inflammation as a primary target. Monocytes, as representatives of the innate immune system, play a major role in the initiation, propagation, and progression of atherosclerosis from a stable to an unstable state. Experimental data support a role of monocytes in acute coronary syndromes and in outcome post-infarction; however, limited research has been done in humans. Analysis of expression of various cell surface receptors allows characterization of the different monocyte subsets phenotypically, whereas downstream assessment of inflammatory pathways provides an insight into their activity. In this review we discuss the functional role of monocytes and their different subpopulations in atherosclerosis, acute coronary syndromes, cardiac healing, and recovery with an aim of critical evaluation of potential future therapeutic targets in atherosclerosis and its complications. We will also discuss technical difficulties of delineating different monocyte subpopulations, understanding their differentiation potential and function.