Abstract
RATIONALE: The chemokine receptor Ccr6 is a G-protein-coupled receptor expressed on various types of leukocytes identified in mouse atherosclerotic lesions. Recent evidence suggests that both CCR6 and its ligand CCL20 are also present in human atheroma; however, their functional roles in atherogenesis remain undefined. OBJECTIVE: Our objective was to delineate the role of Ccr6 in atherogenesis in the apolipoprotein E-deficient (ApoE(-/-)) mouse model of atherosclerosis. METHODS AND RESULTS: Both Ccr6 and Ccl20 are expressed in atherosclerotic aorta from ApoE(-/-) mice. Aortic lesion area in Ccr6(-/-)ApoE(-/-) mice was ∼40% and ∼30% smaller than in Ccr6(+/+)ApoE(-/-) mice at 16 and 24 weeks of age, respectively. Transplantation of bone marrow from Ccr6(-/-) mice into ApoE(-/-) mice resulted in ∼40% less atherosclerotic lesion area than for bone marrow from Ccr6(+/+) mice; lesions in Ccr6(-/-)ApoE(-/-) mice had 44% less macrophage content than lesions in Ccr6(+/+)ApoE(-/-) mice. Ccr6 was expressed on a subset of primary mouse monocytes. Accordingly, Ccl20 induced chemotaxis of primary monocytes from wild-type but not Ccr6(-/-) mice; moreover, Ccl20 induced monocytosis in ApoE(-/-) mice in vivo. Consistent with this, we observed 30% fewer monocytes in circulating blood of Ccr6(-/-)ApoE(-/-) mice, mainly because of fewer CD11b(+)Ly6C(high) inflammatory monocytes. CONCLUSIONS: Ccr6 promotes atherosclerosis in ApoE-deficient mice, which may be due in part to Ccr6 support of normal monocyte levels in blood, as well as direct Ccr6-dependent monocyte migration.