Immunopathogenesis of atherosclerosis: endotoxin accelerates atherosclerosis in rabbits on hypercholesterolemic diet

Implication of natural killer T cells in atherosclerosis development during a LPS-induced chronic inflammation

Atherosclerosis has many features of a chronic inflammatory disease. To evaluate the role of lipopolysaccharide (LPS), mimicking a systemic infection, we administered the endotoxin to apolipoprotein E (apoE)-deficient mice. LPS injections increase the atherosclerotic lesion size and the titer of plasma autoantibodies directed against oxidized low-density lipoprotein. We found that Th1 and Th2 T cells help the activation of B cells in the autoimmune response. The number of interleukin-4 producing natural killer T cells is highly increased in peripheral blood, liver, spleen and thymus cells, as well as in the atherosclerotic plaque of the LPS-treated mice. Finally, an important adventitial infiltrate of activated lymphocytes, sign of an advanced atherosclerosis, is observed only in the LPS-treated mice. Our results demonstrate that LPS administration aggravates atherosclerosis in apoE-deficient mice. LPS-injected apoE-deficient mice appear to be an excellent animal model to analyze the implementation of new therapeutic approaches in the treatment of atherosclerosis by manipulating immunological effectors.

Laser capture microdissection analysis of gene expression in macrophages from atherosclerotic lesions of apolipoprotein E-deficient mice

Macrophage foam cells are integral in the development of atherosclerotic lesions. Gene expression analysis of lesional macrophage foam cells is complicated by the cellular heterogeneity of atherosclerotic plaque and the presence of lesions of various degrees of severity. To overcome these limitations, we tested the ability of laser capture microdissection (LCM) and real-time quantitative reverse transcription PCR to selectively analyze RNA from lesional macrophages of apolipoprotein E (apoE)-deficient mice. Proximal aortic tissue sections were immunostained for macrophagespecific CD68/macrosialin by a rapid (approximately 15-min) protocol. Alternating sections from each animal were used to isolate RNA either from entire sections (analogous to isolation from whole tissue) or by LCM selection of CD68-positive cells. We measured the mRNA levels of CD68, a macrophage-specific marker, alpha-actin, a smooth muscle cell marker, and cyclophilin A, a control gene. Compared with whole sections, CD68 mRNA levels were greatly enriched (33.6-fold) in the laser-captured lesional macrophages. In contrast to whole sections, LCM-derived RNA had undetectable levels of alpha-actin. To illustrate the ability of this method to measure changes in lesional macrophage gene expression, we injected 100 microg of lipopolysaccharide i.p. into apoE-deficient mice and detected in laser-captured lesional macrophages increased mRNA expression for vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, and monocyte chemoattractant protein-1 (11.9-, 32.5-, and 31.0-fold, respectively). By selectively enriching foam cell RNA, LCM provides a powerful approach to study the in situ expression and regulation of atherosclerosis-related genes. This approach will allow the study of macrophage gene expression under various conditions of plaque formation, regression, and response to genetic and environmental perturbations.