Presentations

Abstract

Introduction:

Atherosclerosis is a disease of large/medium-sized vessels characterized by an accumulation of cholesterol-rich LDL within the vessel, chronic immune response, and activation of vascular cells, leading to the formation of plaques and necrotic cores. While not a classical autoimmune disease, previous studies have shown the role of chronic inflammation that persists during the progression of atherosclerosis. Anergy is characterized as a state of unresponsiveness to self-antigens and occurs via intrinsic biochemical and gene-expression changes. While anergy break plays a critical role in autoimmune diseases, evidence suggests an existence of various forms of anergic autoreactive B- cells that may not necessarily induce classical autoimmune pathologies, but rather support low-grade chronic inflammation that is driven by different mechanisms. This study seeks to understand the extent to which atherosclerosis changes the responsiveness of anergic B-cells.

Methods:

We used the p-azophenylarsonate (ARS)-specific mouse model (ARS/A1) which encodes a dual-reactive B-cell receptor (BCR) that binds to ARS and self-antigens. These mice have only anergic B-cells in circulation and can serve as an excellent model to study pathogen mimicry of self-antigens in atherosclerosis. We also used MD4 transgenic mice in which BCR only recognizes hen-egg lysosome and is thus unable to respond to any other stimuli. C57BL/6, ARS/A1, and MD4 mice were injected with an adenovirus vector containing PCSK9 to induce hyperlipidemia. After high-fat diet (HFD) feeding for 12 weeks, plaque burden and stability in collected aortas and hearts were analyzed using ImageJ. The number of peripheral blood anergic B-cells and their functions were also examined in healthy and atherosclerotic Apoe-/- mice.

Results:

Histological analysis of en face Oil Red O-stained aortas showed MD4 had no significant differences compared to control C57BL/6 mice. In contrast, ARS/A1 mice had a significant overall higher atherosclerotic lesion burden throughout the aorta of anergic ARS/A1 mice vs control C57BL/6 mice. Additionally, ARS/A1 mice had a significantly higher aortic lesion burden compared to age- and diet-matched MD4 mice. Histological analysis of picrosirius red-stained aortic valves showed an increase in red birefringence indicating an increase in type I collagen and plaque stability in ARS/A1 mice compared to C57BL/6 mice.

Conclusions:

The lack of differences in atheroprogression in MD4 vs. control suggests that the BCR may not play a critical role in the low-grade chronic inflammation that is seen in atherosclerosis. Alternatively, the abolishment of BCR-signaling in both anti-atherogenic and pro-atherogenic B-cell subsets results in minimal effects in the regulation of plaque burden. The mechanism that drives a higher lesion development in ARS/A1 mice with anergic B-cells compared to BCR-transgenic MD4 mice or C57BL/6 is unclear but could potentially be due to the increased low-level activation of anergic B-cells in the ARS/A1 mice. Further work is needed to examine the effects by which atherosclerosis may change the responsiveness of anergic B-cells and identify specific mechanisms responsible for accelerated plaque burden in ARS/A1 mice.