Abstract 17353: B Cell Depletion Promotes Aortic Infiltration of Tolerogenic Immune Cells and is Protective of Experimental Aortic Aneurysm

Abstract

Anti-CD20 antibody-mediated B cell depletion therapy is widely used for the treatment of B cell malignancies and rheumatoid arthritis. Given the observation that B cells are abundant in abdominal aortic aneurysms (AA), we hypothesize that B cell depletion would be protective of experimental AA formation. C57BL/6j and IL-10 knock-out (KO) mice (male, 8-10 weeks old) were injected intraperitoneal (IP) or intravenous (IV) with mouse monoclonal anti-CD20 IgG2a (or IgG2a control) antibodies at day 7 before and day 7 following induction of AA using the elastase AA perfusion model. AA size was measured at day 14 following perfusion. Depletion of B cell (B1, B2 and IL-10 producing B cells) was confirmed using flow cytometry or immunohistochemistry. IgG and IgM levels were quantified using ELISA. One-way ANOVA was used for data analysis. B1 cells were prominent in peritoneal cavity, whereas B2 cells were spleen and blood. 85-95% of B1 and B2 cells were depleted at day 7 following both IP and IV treatments. Interestingly, both the treatments strikingly suppressed AA growth (control, 96±8%; IP, 62±5%; and IV, 55±4%, p<0.01, n=8-10). Plasma IgM levels were significantly lower (p<0.01), whereas, IgG levels were similar in the B cell depleted mice compared to control mice. Immunohistology showed IL-10 producing B cells were preserved in spleen of B cell depleted mice. B cell depletion in IL-10 KO mice partially suppressed AA formation (control, 111±6%; anti-CD20, 92±8%; n=4-5) suggesting AA growth was partly dependent on IL-10 producing B cells. Flow cytometry revealed presence of CD19+ with B220+ or CD20+, CD138+ (plasma cells), CD1d+ and IgM+IgD+ cells in AA of control mice, which were absent in B cell depleted mice. Despite the preservation of elastin layers, B220+ cells were found the in the AA of B cell depleted mice, which were CD20- and IDO+ (Indole 2,3-dioxygenase), suggesting they are T cell tolerogenic plasmacytoid dendritic cells (pDC). Correlated with this, the CD4+FoxP3+ regulatory T cell population was higher in the aorta of B cell depleted mice. The present results suggest B cell depletion protects mice from experimental AA formation partly via preserving IL-10 producing B cells and promoting the presence of tolerogenic pDCs in the aorta.