Treatment with a Toll-like Receptor 7 ligand evokes protective immunity against atherosclerosis in hypercholesterolaemic mice

BACKGROUND

The interplay between innate and adaptive immunity is central in life-threatening clinical complications of atherosclerosis such as myocardial infarction and stroke. The specific mechanisms involved and their protective versus detrimental effects in the disease process remain poorly understood. We have previously shown that higher levels of Toll-like receptor 7 (TLR7) expression in human atherosclerotic lesions are correlated with better patient outcome.

OBJECTIVE

In this study, we explored whether TLR7 activation can ameliorate disease in experimental atherosclerosis in mice.

METHODS

Apolipoprotein E deficient mice (Apoe^-/- ) with established disease were injected for five weeks intraperitoneally with the TLR7 ligand R848. Local effects were evaluated by characterization of the lesion. Systemic effects of the treatment were investigated by immune composition analysis in the spleen and plasma measurements.

RESULTS

The in vivo treatment arrested lesion progression in the aorta. We also detected expansion of marginal zone B cells and T_reg in the spleen together with increased plasma IgM antibodies against oxidized low-density lipoprotein (oxLDL) and reduced plasma cholesterol levels. These changes were accompanied by increased accumulation of IgM antibodies, decreased necrosis and fewer apoptotic cells in atherosclerotic lesions.

CONCLUSIONS

Our findings show that TLR7 stimulation could ameliorate atherosclerotic lesion burden and reduce plasma cholesterol in Apoe^-/- mice. TLR7 stimulation was associated with an atheroprotective B-cell and T_reg response, which may have systemic and local effects within lesions that could prevent arterial lipid accumulation and inflammation.

Neural reflex control of vascular inflammation

Atherosclerosis is a multifactorial chronic inflammatory disease that underlies myocardial infarction and stroke. Efficacious treatment for hyperlipidemia and hypertension has significantly reduced morbidity and mortality in cardiovascular disease. However, atherosclerosis still confers a considerable risk of adverse cardiovascular events. In the current mechanistic understanding of the pathogenesis of atherosclerosis, inflammation is pivotal both in disease development and progression. Recent clinical data provided support for this notion and treatment targeting inflammation is currently being explored. Interestingly, neural reflexes regulate cytokine production and inflammation. Hence, new technology utilizing implantable devices to deliver electrical impulses to activate neural circuits are currently being investigated in treatment of inflammation. Hopefully, it may become possible to target vascular inflammation in cardiovascular disease using bioelectronic medicine. In this review, we discuss neural control of inflammation and the potential implications of new therapeutic strategies to treat cardiovascular disease.