Lymph nodes grow rapidly and robustly at the initiation of an immune response, and this growth is accompanied by growth of the blood vessels. Although the vessels are critical for supplying nutrients and for controlling cell trafficking, the regulation of lymph node vascular growth is not well understood. We show that lymph node endothelial cells begin to proliferate within 2 d of immunization and undergo a corresponding expansion in cell numbers. Endothelial cell proliferation is dependent on CD11c+ dendritic cells (DCs), and the subcutaneous injection of DCs is sufficient to trigger endothelial cell proliferation and growth. Lymph node endothelial cell proliferation is dependent on vascular endothelial growth factor (VEGF), and DCs are associated with increased lymph node VEGF levels. DC-induced endothelial cell proliferation and increased VEGF levels are mediated by DC-induced recruitment of blood-borne cells. Vascular growth in the draining lymph node includes the growth of high endothelial venule endothelial cells and is functionally associated with increased cell entry into the lymph node. Collectively, our results suggest a scenario whereby endothelial cell expansion in the draining lymph node is induced by DCs as part of a program that optimizes the microenvironment for the ensuing immune response.

Background— Kawasaki disease is the most common cause of acquired cardiac disease and acute vasculitis in children, targets the coronary arteries, and can occasionally be fatal. The pathogenesis and the molecular mechanisms remain unknown. After injection of Lactobacillus casei cell-wall extract (LCCWE), mice develop a focal coronary arteritis that histopathologically resembles Kawasaki disease, but the mechanism remains unclear. Here, we tested the hypothesis that signaling by Toll-like receptors (TLRs) through their key downstream adaptor molecule myeloid differentiation factor 88 (MyD88) is required for the cellular activation and coronary arteritis produced by LCCWE. Methods and Results— Bone marrow–derived macrophages from TLR2- or MyD88-deficient mice were unresponsive to LCCWE-induced stimulation. In contrast, macrophages obtained from TLR4-deficient mice produced the same amount of interleukin-6 as macrophages from wild-type mice after stimulation with LCCWE. Intraperitoneal injection of LCCWE produced severe focal coronary arteritis in TLR4 −/− and C57BL/6 control mice but not in TLR2 −/− or MyD88 −/− mice. Collectively, these results indicate that LCCWE is a potent inducer of nuclear factor-κB via TLR2 but not TLR4 and that this activation proceeds via the MyD88-dependent signaling pathway. In vivo studies suggest that TLR2 −/− mice are protected from LCCWE-induced coronary arteritis and that this protection is mediated through the adaptor molecule MyD88. Conclusions— Our results provide important insights into the molecular signaling in this mouse model of coronary arteritis. We show here that LCCWE-induced coronary arteritis is dependent on intact TLR2 and MyD88 signaling.

Objective. To examine the ability of mature dendritic cells (DCs) or macrophages intentionally exposed to lipopolysaccharide or apoptotic or necrotic cells to break tolerance in normal mice.Methods. We adoptively transferred into C57BL/6 mice a variety of syngeneic myeloid antigen-presenting cell populations exposed to different activation stimuli as well as to meals of necrotic and apoptotic cells. We studied expression of autoimmunity in the immunized mice by serologic evaluation of autoantibody production, subclass analysis of Ig production, clinical evidence of kidney disease, glomerular immune complex deposition, and renal pathology.Results. Injection of mice with DCs incubated with apoptotic or necrotic cells, as well as, surprisingly, with DCs cultured in media alone, induced high levels of IgG autoantibodies, including anti-double-stranded DNA (anti-dsDNA) antibodies. In striking contrast, transfer of equivalent-treated macrophages failed to generate IgG autoantibodies. IgG was deposited in the kidneys of mice vaccinated with DCs, but despite high levels of anti-dsDNA antibodies, these mice did not develop overt nephritis. Serologic evaluation of the antibody response revealed that the mice primarily developed elevated levels of IgG1 antibodies, including high levels of IgG1 anti-dsDNA.Conclusion. The data suggest that mature myeloid DCs are able to break tolerance and induce lupus autoantibodies in normal hosts, but that other susceptibility factors must be in place to induce long-lasting autoimmunity and clinical expression of disease.