Atherosclerosis is modulated by immune cells. Understanding the diversity and heterogeneity in the aorta in steady state, as well as during different stages of disease will help to determine mechanisms promoting disease progression. To characterize the immune cells, we performed single cell RNA sequencing of aortic CD45+ leukocytes from C57BL/6 (WT) on chow diet and early disease Ldlr-/- mice fed high fat diet (HFD) for 21-days. The single cell RNA-seq analyses revealed the heterogeneity of aortic macrophages in steady state and early atherosclerotic disease. Overall design: Single cell RNA sequencing of aortic CD45+ cells from nascent (n=10, C57BL/6 8-weeks age) and early atherosclerotic Ldlr-/- mice (n=10, HFD 21-days), using Illumina HiSeq4000.