IL-9 aggravates the development of atherosclerosis in ApoE-/- mice.

Aims: Recently, interleukin (IL)-9 was found to be involved in the pathogenesis of many inflammatory diseases. Here, we tested whether IL-9 was related to atherosclerosis and investigated the underlying mechanisms.

Methods And Results: IL-9R was expressed in mouse aortic endothelial cells (MAECs) and aortic tissues, and IL-9 levels were elevated in plasma and aortic arches in Apolipoprotein E-deficient (ApoE-/-) mice. ApoE-/- mice fed a western diet for 10 weeks were administered recombinant mouse IL-9 (rIL-9) or anti-IL-9 neutralizing monoclonal antibody (mAb). Mice treated with rIL-9 developed markedly larger plaques in both the aorta and aortic root. Immunohistochemical studies demonstrated increases in both vascular endothelial adhesion molecule-1 (VCAM-1) expression and the infiltration of inflammatory cells, including T cells and macrophages, in plaques. However, treatment with the anti-IL-9 mAb caused the opposite effect. The administration of rIL-9 did not affect the splenic T cell or peripheral monocyte subsets. Meanwhile, IL-9 induced VCAM-1 expression in MAECs mainly via a STAT3-dependent pathway, consequently increasing monocyte-endothelial adhesion. Moreover, treatment with anti-VCAM-1 mAb partially abrogated the IL-9-induced increase in plaque area. In addition, CD4(+)IL-9(+) T cells and IL-9 were increased in patients with acute coronary syndrome, and the levels of IL-9 in culture supernatants and soluble VCAM-1 (sVCAM-1) in plasma were significantly positively correlated in the enrolled patients.

Conclusion: Our results demonstrated that IL-9 exerted pro-atherosclerotic effects in ApoE-/- mice at least partially by inducing VCAM-1 expression, which mediated inflammatory cell infiltration into atherosclerotic lesions.