Raising Endogenous Anti-HMGB1 IgM Antibody for Athero-Protection in the Apoe−/− Mouse Model of Atherosclerosis

Abstract

Atherosclerosis is driven partly by inflammation, mediated mainly by pro-inflammatory mediators/cytokines. Previous studies have revealed the role of HMGB1, a prototypic DAMP (damage-associated molecular pattern) molecule, in atherogenesis. Recently, we have found that there is a spontaneous production of a neutralizing anti-HMGB1 IgM antibody in the Apoe−/− mouse model of atherosclerosis and healthy humans. In the present study, we have determined whether raising the anti-HMGB1 IgM, via immunization targeting HMW4 (a dominant epitope of HMGB1), reduces atherosclerosis. We first showed that the immunization of 8-week-old Apoe−/− C57BL/6 mice increased the HMW4-specific B-1 cells (which produce anti-HMW4 IgM), identified by HMW4-tetramer staining/flow cytometry. Next, we assessed the anti-atherogenic efficacy of the immunization. To the end, 8-week-old Apoe−/− mice were divided into 4 groups (n = 10/group). Each group was treated with: 1) HMW4 (“test”); 2) raHMW4 (randomized control peptide) (“control”); 3) depletion of the HMW4-specific B cells (to prevent the production of anti-HMW4 IgM), followed by the immunization (control for B cell dependence); or 4) none. At 12 weeks of age, mice were fed a western type diet (WTD) for 12 weeks. Lesions in treated mice were then quantified, by both en face analysis of the aortic arch and morphometric analysis of ORO-stained sections of the aortic root. The “test” group showed reduction in atherosclerosis (by ~40%), when compared to the “control” group (p = 0.006) or non-treated group (p = 0.01). Such reduction was diminished when the anti-HMW4 IgM-producing B cells were depleted (p = 0.02). This study raises the possibility to amplify the anti-HMGB1 IgM response to reduce atherosclerosis.