Deficiency in Lymphotoxin β Receptor Protects From Atherosclerosis in apoE-Deficient Mice

Rationale: Lymphotoxin beta receptor (LTbR) regulates immune cell trafficking and communication in inflammatory diseases. However, the role of LTbR in atherosclerosis is still unclear. Objective: The aim of this study was to elucidate the role of LTbR in atherosclerosis. Methods and Results: After 15 weeks of feeding a Western-type diet, mice double-deficient in apolipoprotein E and LTbR (apoE(-/-)/LTbR-/-) exhibited lower aortic plaque burden than did apoE(-/-) littermates. Macrophage content at the aortic root and in the aorta was reduced, as determined by immunohistochemistry and flow cytometry. In line with a decrease in plaque inflammation, chemokine (C-C motif) ligand 5 (Ccl5) and other chemokines were transcriptionally downregulated in aortic tissue from apoE(-/-)/LTbR-/- mice. Moreover, bone marrow chimeras demonstrated that LTbR deficiency in hematopoietic cells mediated the atheroprotection. Furthermore, during atheroprogression, apoE(-/-) mice exhibited increased concentrations of cytokines, for example, Ccl5, whereas apoE(-/-)/LTbR-/- mice did not. Despite this decreased plaque macrophage content, flow cytometric analysis showed that the numbers of circulating lymphocyte antigen 6C (Ly6C)(low) monocytes were markedly elevated in apoE(-/-)/LTbR-/- mice. The influx of these cells into atherosclerotic lesions was significantly reduced, whereas apoptosis and macrophage proliferation in atherosclerotic lesions were unaffected. Gene array analysis pointed to chemokine (CC motif) receptor 5 as the most regulated pathway in isolated CD115(+) cells in apoE(-/-)/LTbR-/- mice. Furthermore, stimulating monocytes from apoE(-/-) mice with agonistic anti-LTbR antibody or the natural ligand lymphotoxin-alpha 1 beta 2, increased Ccl5 mRNA expression. Conclusions: These findings suggest that LTbR plays a role in macrophage-driven inflammation in atherosclerotic lesions, probably by augmenting the Ccl5-mediated recruitment of monocytes.