Limited proliferation capacity of aorta intima resident macrophages requires monocyte recruitment for atherosclerotic plaque progression

Early atherosclerosis depends upon responses by immune cells resident in the intimal aortic wall. Specifically, the healthy intima is thought to be populated by vascular dendritic cells (DC) that, during hypercholesterolemia, initiate atherosclerosis by being the first to accumulate cholesterol. Whether these cells remain key players in later stages of disease is unknown. Using murine lineage tracing models and gene expression profiling, we reveal that myeloid cells present in the intima of the aortic arch are not DCs but instead specialized aorta intima resident macrophages (Mac(AIR)) that depend upon Csf-1 and sustained by local proliferation. Although Mac(AIR) comprise the earliest foam cells in plaques, their proliferation during plaque progression is limited. After months of hypercholesterolemia, their presence in plaque is overtaken by recruited monocytes, which induce Mac(AIR)-defining genes. These data redefine the lineage of intimal phagocytes and suggest that proliferation is insufficient to sustain generations of macrophages during plaque progression.