Abstract 156: Cholesterol-Induced IL-1 Expression Promotes Regulatory T Cells to Effector T Cells Redifferentiation in Atherosclerotic Lesions

Abstract

Regulatory T cells (Treg) can suppress proatherogenic T cell responses, similar to their established function in regulating autoreactive T cells in immune-mediated/inflammatory disease. We have shown that hypercholesterolemia induces an accumulation of Treg in atherosclerotic aorta, but the Treg content is not maintained over time under sustained hypercholesterolemic conditions. Significantly, effector T cells (Teff) content in the aorta increased while Treg content went down concomitant with increase of the lesion size over this time period. Previous studies have shown that Treg change phenotype in vivo under inflammatory conditions and some studies indicate that IL-1 promotes differentiation of Th17 cells both from naïve precursors, and the conversion of Treg to Th17. The general hypothesis for this study is that the loss of lesional Treg over time may reflect a conversion of recruited Treg into Teff cells, due to the influence of the lesional inflammatory conditions, including production of IL-1. We have conducted preliminary studies in vitro showing that cholesterol crystals (CHC)-induced macrophage inflammasome activation modifies Treg phenotype. Thioglycollate elicited peritoneal macrophages from wildtype mice produced high levels of IL1 after CHC treatment compared to macrophages from caspase-1-null mice and this response induced IL-17 and IFNgamma expression by purified Treg from Foxp3-GFP TCR transgenic mice. We have also demonstrated, by confocal microscopy of sections from spleen or aortic arch of Ldlr -/- mice under cholesterol diet for 10 weeks, that macrophages but not dendritic cells uptake CHC in vivo. Moreover, IL-1 gene expression in aortas of Ldlr -/- mice is minimal after 4 weeks of cholesterol diet, but significantly rises after 8 weeks. This result correlated also with an increase of the levels of IFNgamma and Tbet and changes in numbers of IL17 or Foxp3 positive cells observed in collagen digest of aortas from Ldlr-/-/Foxp3-GFP/IL17-RFP. These results indicate that arterial IL-1 expression, which can be induced by CHC in macrophages under hypercholesterolemic conditions, accompanies a reduction in the Treg:Th1 ratio. Current work is focused on determining if atherosclerotic lesion development can be blocked by maintaining a sufficient ratio of atheroantigen-specific Treg:Teff cells through pharmacologic manipulation of inflammasome activation.