Induction of oral tolerance to oxidized low-density lipoprotein ameliorates atherosclerosis.

BACKGROUND: Oxidation of low-density lipoprotein (LDL) and the subsequent processing of oxidized LDL (oxLDL) by macrophages results in activation of specific T cells, which contributes to the development of atherosclerosis. Oral tolerance induction and the subsequent activation of regulatory T cells may be an adequate therapy for the treatment of atherosclerosis. METHODS AND RESULTS: Tolerance to oxLDL and malondialdehyde-treated LDL (MDA-LDL) was induced in LDL receptor-/- mice fed a Western-type diet by oral administration of oxLDL or MDA-LDL before the induction of atherogenesis. Oral tolerance to oxLDL resulted in a significant attenuation of the initiation (30% to 71%; P<0.05) and progression (45%; P<0.05) of atherogenesis. Tolerance to oxLDL induced a significant increase in CD4+ CD25+ Foxp3+ cells in spleen and mesenteric lymph nodes, and these cells specifically responded to oxLDL with increased transforming growth factor-beta production. Tolerance to oxLDL also increased the mRNA expression of Foxp3, CTLA-4, and CD25 in the plaque. In contrast, tolerance to MDA-LDL did not affect atherogenesis. CONCLUSIONS: OxLDL-specific T cells, present in LDL receptor-/- mice and important contributors in the immune response leading to atherosclerotic plaque, can be counteracted by oxLDL-specific CD4+ CD25+ Foxp3+ regulatory T cells activated via oral tolerance induction to oxLDL. We conclude that the induction of oral tolerance to oxLDL may be a promising strategy to modulate the immune response during atherogenesis and a new way to treat atherosclerosis.

Delivery of Chlamydia pneumoniae to the vessel wall aggravates atherosclerosis in LDLr-/- mice.

OBJECTIVE: The role of Chlamydia pneumoniae in atherosclerosis is still debated. In this study a novel mouse model was applied to determine the direct impact of C. pneumoniae on the arterial wall and the development of atherosclerosis. METHODS: Direct effects of C. pneumoniae on collar-induced atherosclerosis were studied after local delivery of C. pneumoniae to carotid arteries of LDL receptor-deficient (LDLr-/-) mice. RESULTS: The presence of C. pneumoniae in the vessel wall was quantified by RT-PCR (6.2 x 10(4) copies/artery) and resulted in a 2.0-fold increase in intima/media ratios (p<0.05) and a 1.7-fold increase in stenosis (p<0.05). Immunostaining revealed a 2.98-fold (p<0.01) increased macrophage content and a tendency towards lower numbers of smooth muscle cells and collagen in lesions of infected carotid arteries. Direct delivery of another respiratory pathogen, Mycoplasma pneumoniae, to the carotids did not affect size or composition of the atherosclerotic lesions. Presence of C. pneumoniae in the carotid arteries resulted within 7 days in a marked upregulation of the expression of MCP-1 (p<0.01) and ICAM-1 as determined on mRNA and protein levels. These in vivo data were in line with data obtained with in vitro infections of macrophages and endothelial cells with C. pneumoniae. CONCLUSIONS: We conclude that C. pneumoniae in carotid arteries leads to more pronounced atherosclerotic lesions with a more vulnerable morphology and that this model is suitable to monitor direct effects of C. pneumoniae on atherogenesis.

Blockade of interleukin-12 function by protein vaccination attenuates atherosclerosis.

BACKGROUND: Interleukin-12 (IL-12) has been identified as a key inducer of a type 1 T-helper cell cytokine pattern, which is thought to contribute to the development of atherosclerosis. We sought to study the role of IL-12 in atherosclerosis by inhibition of IL-12 using a newly developed vaccination technique that fully blocks the action of IL-12. METHODS AND RESULTS: LDL receptor-deficient (LDLr(-/-)) mice were vaccinated against IL-12 by 5 intramuscular injections of IL-12-PADRE complex in combination with adjuvant oil-in-water emulsion (low dose)/MPL/QS21 every 2 weeks. Two weeks thereafter, atherogenesis was initiated in the carotid artery by perivascular placement of silicone elastomer collars. IL-12 vaccination resulted in the induction of anti-IL-12 antibodies that functionally blocked the action of IL-12 as determined in an IL-12 bioassay. Blockade of IL-12 by vaccination of LDLr(-/-) mice resulted in significantly reduced (68.5%; P<0.01) atherogenesis compared with control mice without a change in serum cholesterol levels. IL-12 vaccination also resulted in a significant decrease in intima/media ratios (66.7%; P<0.01) and in the degree of stenosis (57.8%; P<0.01). On IL-12 vaccination, smooth muscle cell and collagen content in the neointima increased 2.8-fold (P<0.01) and 4.2-fold (P<0.01), respectively. CONCLUSIONS: Functional blockade of endogenous IL-12 by vaccination resulted in a significant 68.5% reduction in atherogenesis in LDLr(-/-) mice. Vaccination against IL-12 also improved plaque stability, from which we conclude that the blockade of IL-12 by vaccination may be considered a promising new strategy in the treatment of atherosclerosis.