Expression of interleukin-15 in mouse and human atherosclerotic lesions

Atherosclerotic lesions are characterized by prominent macrophage and T-cel l infiltration and atherosclerosis is widely recognized as an inflammatory disease. The cytokine interleukin-15 (IL-15) has T-cell chemotactic and pro -inflammatory properties and promotes the recruitment of T cells to sites o f inflammation. We have therefore examined IL-15 expression in the atherosc lerotic ApoE-deficient mouse model as well as in human atherosclerotic lesi ons. In gene expression arrays, a transcript corresponding to IL-15 mRNA wa s elevated in atherosclerotic aortas of ApoE-deficient mice fed a Western d iet for 10 and 20 weeks, corresponding to lesions of the fatty streak and f ibrofatty plaque stage, respectively. Immunostaining for IL-15 localized to aortic smooth muscle cells in nonatherosclerotic C57BL/6 mice, whereas bot h macrophages and smooth muscle cells stained positive for IL-15 in atheros clerotic lesions of ApoE-deficient mice. Finally, advanced atherosclerotic lesions of human carotid arteries were immunostained to determine whether I L-15 is involved in human disease. IL-15 protein was present also in the hu man lesions with a distribution primarily overlapping that of macrophages. In conclusion, IL-15 is up-regulated in both human and animal atherosclerot ic lesions and may contribute to the recruitment of T cells and their activ ation during atherogenesis.