Objective The purpose of this study was to establish a reliable, chronic model of abdominal aortic aneurysm (AAA). Materials and methods 120 eight-week old C56BL/6 male mice were equally divided into three groups: 1) BAPN Group: 0.2% 3-aminopropionitrile fumarate salt (BAPN) drinking water was provided to mice two days before surgery until the end of study. Sham aneurysm induction surgery was performed using 5 μl of heat de-activated elastase. 2) Elastase Group: Mice were given regular drinking water without BAPN. During aneurysm induction surgery, 5 μl of active form elastase (10.3mg protein/ml, 5.9units/mg protein) was applied on top of adventitia of infrarenal abdominal aorta for 5 minutes. 3) BAPN+Elastase Group: Mice were given both BAPN drinking water and active form of elastase application as above. On post-operative days 7, 14, 21, 28 and 100, aortic samples were collected for histology, cytokine array and gelatin zymography after aortic diameter measurement. Results Compared with Elastase group, BAPN+Elastase group had higher AAA formation rate (93% vs 65%, P < .01) with more advanced-staged AAAs (25/42 vs 1/40 for Stage II & III, P < .001). Aneurysms from the BAPN+Elastase Group demonstrated persistent long-term growth (221.5 ± 36.6%, 285.8 ± 78.6%, 801 ± 160% on day 21, 28 and 100 respectively, P ˂ .001), with considerable thrombus formation (54%) and rupture (31%) at the advanced stages of AAA development. Cytokine levels (pro-MMP9, IL-1β, IL-6, CCL-5, TREM-1, MCP-1 and TIMP-1) in BAPN+Elastase Group were higher than Elastase Group on day 7. After day 7, cytokine levels returned to baseline with the exception of elevated MMP2 activity. By histology, CD3⁺T cells in the BAPN+Elastase Group were elevated on days 28 and 100. Conclusions A combination of oral BAPN administration and peri-aortic elastase application induced a chronic, advanced staged AAA with characteristics of persistent aneurysm growth, thrombus formation, and spontaneous rupture. Future studies should utilize this model, especially for examining tissue remodeling during the late stages of aneurysm development.

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Objective B cell depletion therapy is widely used for treatment of cancers and autoimmune diseases. B cells are abundant in abdominal aortic aneurysms (AAA), however, it is unknown whether B cell depletion therapy affects AAA growth. Using experimental models of murine AAA, we aim to examine the effect of B cell depletion on AAA formation. Approach and Results Wild-type or Apolipoprotein E knockout mice were treated with mouse monoclonal anti-CD20 or control antibodies and subjected to an elastase perfusion or angiotensin II-infusion model to induce AAA, respectively. Anti-CD20 antibody treatment significantly depleted B1 and B2 cells, and strikingly suppressed AAA growth in both models. B cell depletion resulted in lower circulating IgM levels, but did not affect the levels of IgG or cytokine/chemokine levels. Although the total number of leukocyte remained unchanged in elastase perfused aortas following anti-CD20 antibody treatment, the number of B cell subtypes was significantly lower. Interestingly, plasmacytoid dendritic cells (pDCs) expressing the immunomodulatory enzyme indole 2,3-dioxygenase (IDO) were detected in the aortas of B cell depleted mice. In accordance with an increase in IDO+ pDCs, the number of regulatory T cells was higher while the expression of pro-inflammatory genes was lower in aortas of B cell depleted mice. In a coculture model, presence of B cells significantly lowered the number of IDO+ pDCs without affecting total pDC number. Conclusions The present results demonstrate that B cell depletion protects mice from experimental AAA formation and promotes emergence of an immunosuppressive environment in aorta.