Abstract 293: Id3 Regulates High-Fat-Diet--Induced IgG2c Production
Background: High-fat diet (HFD)-induced adipose tissue inflammation leads to insulin resistance and glucose intolerance, increasing the risk of cardiovascular disease. Recently, B cells and IgG antibodies have been shown to promote the metabolic consequences of obesity. HFD induces IgG2c production - an IgG isotype that promotes inflammatory disorders. Mice null for Id3, a helix-loop-helix protein known to mediate IgG2c responses in vivo, develop significantly attenuated HFD-induced obesity; raising the interesting hypothesis that Id3 promotes HFD-induced obesity by mediating HFD-induced IgG2c production.
Methods and results: Western Blot analysis revealed that primary splenic B cells stimulated with IFN + CD40L (an IgG2c-inducing cocktail) expressed significantly greater amounts of Id3 protein compared to B cells treated with CD40L alone ((1.26+/-0.05 vs 0.88+/-0.03; n=3; p=0.003). ELISA determination of immunoglobulin levels from whole adipose tissue of fed C57Bl/6J (WT) mice fed a HFD (60% kcal fat) revealed a 4 fold increase in IgG2c (3810+/-789 ng vs 993+/-422 ng; n=5; p=0.01) - but not IgM, IgG1, or IgG2b - compared to chow-fed controls. No differences in serum IgG2c were observed. In contrast, HFD-induced adipose tissue IgG2c levels were significantly attenuated in Id3-/- mice (1643+/-493 vs 889+/-272 ng; n=6-7; p=0.19), despite the fact that Id3-/- mice had significantly more adipose tissue B cells per (g) fat compared to WT (1.6E5+/-0.2E5 vs 0.5E5+/-0.09E5; n=5; p=0.001).
Conclusions: Id3 promotes HFD-induced local adipose tissue IgG2c production; an effect not dependent on B cell number. Studies in animals with B cell-specific loss of Id3 are ongoing to identify the mechanisms whereby Id3 mediates HFD-induced IgG2c production and downstream metabolic effects.
- © 2012 by American Heart Association, Inc.