Abstract 517: CX3CR1, a Cardiovascular Disease Risk Gene, Regulates Tissue-Damaging Effector Functions of T Cells Accumulated in the Atherosclerotic Plaque
Selected T-cell subsets accumulate in the atherosclerotic plaque, including CD4+CD28− T cells which are highly efficient in killing endothelial cells and vascular smooth muscle cells (VSMC), implicating them in plaque destabilization. Signals activating plaque-residing CD4+CD28− T cells to mediate cytotoxicity are unknown, but CD4+CD28− T cells typically express CX3CR1, a molecule identified as a cardiovascular disease risk gene. We have examined how the CX3CR1 ligand fractalkine (FKN) affects effector functions of CD4+CD28− T cells. FKN transcripts were detected in 8 of 10 atheromas from carotid endarterectomies, and cytokine stimulation (IFN-γ and TNF-α) of coronary artery smooth muscle cells (CASMCs) upregulated FKN surface expression. Expression of CX3CR1 was a feature of CD4+CD28− but not CD4+CD28+ T cells isolated freshly from carotid plaque. Binding of FKN markedly amplified the T cell receptor-mediated signal as demonstrated by testing T-cell effector functions with artificial antigen-presenting cells stably transfected with FKN. FKN costimulation of CD4+CD28− T cells (but not of CD4+CD28+ T cells) resulted in a 2-fold increase of IFN-γ production and granule exocytosis. The impact of FKN on T cell-mediated killing was explored by transfecting CASMCs with FKN or a control vector and culturing them with CD4+CD28+ and CD4+CD28− T cells harvested from ACS patients. FKN overexpression rendered CASMCs highly susceptible to cytotoxic death induced by CD4+CD28− T cells (P < 0.001 compared to CD4+CD28+ T cells). Blocking CX3CR1-FKN interactions through soluble FKN protected CASMCs. Finally, we assessed T cell-mediated and FKN-dependent CASMC killing in patients with different CX3CR1 genotypes. In patients carrying the ACS-linked genotype I249-M280, T cells were significantly more efficient in inducing FKN-dependent CASMC apoptosis (n = 21, P < 0.001). CX3CR1-FKN interactions regulate tissue injurious effector functions of CD4+CD28− T cells accumulated in the inflamed plaque, including the killing of VSMC. Killing efficiency of CD4+CD28− T cells depends upon the CX3CR1 genotype, implicating this disease risk gene into a novel effector pathway leading to plaque instability.