Presentations

Abstract

Introduction: Atherosclerosis is a disease that is primarily characterized by the build-up of fatty lesions in large and medium-sized vessels, chronic inflammation, dyslipidemia, and obesity. It is the leading cause of death worldwide, contributing to 25% of deaths in the United States. Cells of both the innate and adaptive immune systems, especially B cell subsets, play a complex role in the development of plaque formation during atherosclerosis. Innate response activator (IRA) and follicular (FO) B cells are known to be pro-atherogenic via Type I T-helper cell (Th1) responses, inflammatory cytokine, and immunoglobulin production. On the other hand, B1, and marginal zone (MZ) cells show protective functions in atherosclerosis via T follicular helper cell (Tfh) suppression and IgM antibody (Ab) secretion. B1 cells produce immunoglobulin A (IgA) Abs that are crucial for mucosal immunity. Gut microbiota plays an important role in shaping the immune system during the early stages of life. IgA Abs are involved in maintaining intestinal homeostasis and have the ability to mediate protective immunity. Interestingly, studies have shown a close relation between altered gut microbiota and presence of bacterial populations within atherosclerotic plaques and atherogenesis. However, the role of IgA in atherogenesis development is still largely unknown. In this study, we investigate the role of IgA not only in the development of atherosclerosis but also in gut health and examine the extent to which IgA deficiency can alter the immune response in peripheral tissues and aorta.

Methods: IgA deficient low-density lipoprotein-deficient receptor (IgA-/-Ldlr-/-) and control Ldlr-/- mice were fed a high-fat diet (HFD) for ~14-18 weeks to induce hyperlipidemia and the development of atherosclerotic lesions. Additionally, we treated some of the mice with 4kDa fluorescein isothiocyanate (FITC)-dextran (FD4) via oral gavage, 45mins prior to tissue collection, for assessing intestinal permeability. We conducted subsequent cholesterol assays and measured lesion formation in the aorta (en face staining with Oil Red-O) and the brachiocephalic artery (BCA-branch between the aortic arch and the "fork" split of the carotid and the subclavian arteries). Blood, peritoneal lavage, spleen, omentum, mesenteric lymph nodes, Peyer's patches, aorta, and small intestines were collected and processed with a fluorescence spectrophotometer (FACS) to assess immune cell distribution and activation. Hearts and guts were collected for subsequent cryo-sectioning and staining to measure plaque development (histology).

Results: We observed statistically significant (p<=0.05) reduction in plaque development in IgA-/-Ldlr-/-mice compared to the control Ldlr-/- mice, post en face aorta analysis and BCA grading. These results correlated with a significant reduction of total plasma cholesterol level in IgA-/-Ldlr-/- mice. Although cells counts from the spleen and peritoneal lavage had no significant difference, the omentum and carotids had significantly (p<=0.05) increased cell count within the IgA-/-Ldlr-/-mice compared to the Ldlr-/- control mice. Additionally, we observed sex-specific differences between the IgA-/-Ldlr-/- and Ldlr-/- mice. Further analysis of intestinal permeability test, flow cytometry and histology data are underway.

Conclusion: Our data so far suggest IgA acting in a site-specific manner and plays an unexpected inflammatory role during atherosclerosis, especially by altering the local immune composition. In vivo data from FD4 gavage would help us in uncovering the role of IgA in gut permeability. Future work would focus on identifying and analyzing the sites of IgA functionality and developing methods to understand the mechanisms involved in lesion formation in the aortic valves and the aorta during atherogenesis.