Abstract 90: The Atheroprotective Effects of Id3 Are Linked to B-1a Cell Proliferation and Plasma Levels of E06
Background: The HLH transcription factor, Id3, is essential for B cell-mediated atheroprotection in mice and a functionally significant single nucleotide polymorphism in the human ID3 gene at rs11574 is associated with carotid intimal medial thickness in humans. Yet, the mechanisms mediating Id3 atheroprotection are poorly understood. Recent studies provide clear evidence that B cell effects on atherosclerosis are subset dependent; with B2 cells promoting and B-1a cells attenuating atherosclerosis in a sIgM-dependent manner. Innate, natural IgM antibodies, such as E06, recognize oxidized phospholipids, are produced by B-1a cells, and inhibit atherogenesis. Therefore, we hypothesized that Id3 would regulate plasma levels of E06 IgM and atheroprotective B-1a cells.
Methods & Results: Id3-/-ApoE-/- mice (n = 9) at 8 weeks old had lower plasma levels of E06 compared to control Id3+/+ApoE-/- mice (n = 9) (1500 vs. 2750 RLU, p < 0.05) as measured by ELISA. This was not due to lower total IgM (270 vs. 100 ug/mL respectively, p < 0.05). ApoB-100 levels were not different (1500 vs 1600 RLU, n.s.). Consistent with plasma data, the number of B-1a cells, assessed by flow cytometry, was lower in Id3-/-ApoE-/- (n = 5) compared to Id3+/+ApoE-/- mice (n = 4) (0.8 x105 vs 3.0 x105, p < 0.05). There was no difference in transcript levels, as measured by real-time PCR, of E06 or sIgM in fluorescence-activated cell sorted B-1a cells. Furthermore, we found decreased homeostatic proliferation, measured by in situ CFSE dilution, of B-1a cells in Id3-/-ApoE-/- mice (n = 5) compared to control mice (n = 5) (30.1% vs. 50.0%, p = 0.001). Additionally, humans with the functionally significant polymorphism in ID3 had lower plasma levels of IgM to MDA-LDL (n = 97, trend with p = 0.08) and no difference in IgG as measured by ELISA.
Conclusion: Taken together, these data suggest a novel role for Id3 in regulating B-1a cell proliferation, resulting in reduced plasma levels of the atheroprotective natural antibody, E06. Moreover, the data suggest that the ID3 polymorphism in humans at rs11574 may link protective IgM to modified lipids with vascular disease.
- © 2012 by American Heart Association, Inc.