Atherosclerosis is known to be controlled by regulatory T cells (Tregs), but neither the antigen specificity nor the location nor the mechanism by which these cells protect are known. Project 4 is testing the hypothesis that regulatory CD4 T cells express and secrete IL-10 in response to their cognate antigen, ApoB, the main core protein of low density lipoprotein (LDL). This is based on the discovery of a significant number of ApoB-specific CD4 T cells in mice and in humans, using mouse and human MHC-II tetramers and dextramers loaded with mouse and human ApoB peptides, respectively.
Specific Aim 1 is to test this hypothesis in mice by studying atherosclerosis in Apoe-/- mice and following the natural history of the ApoB-specific CD4 T cell repertoire by flow cytometry (FACS), mass cytometry (CyTOF) and RNA-Seq (through core E). To conclusively test whether IL-10 from ApoB-specific CD4 T cells is required for atheroprotection, we will harvest ApoB-specific CD4 T cells from Apoe-/- (IL-10 sufficient) or CD4CreIl10fl/flApoe-/- (IL-10-deficient) donors and separately transfer them into recipient Apoe-/- Cd4-/- mice. We hypothesize that the IL-10 sufficient CD4 T cells will be atheroprotective and the IL-10 deficient CD4 T cells will not.
Specific Aim 2 is to translate the findings to humans, using frozen PBMCs from the MESA cohort (core D) and the UVa cohort (core C). Preliminary data show that we can detect human ApoB-specific CD4 T cells in frozen PBMCs from subjects with subclinical cardiovascular disease (CVD). We propose to test their ability to express (by FACS) and secrete (by EliSpot) IL-10, assess their phenotype by CyTOF and define their transcriptome by RNA-Seq (through core E). We have discovered 30 human ApoB peptides that bind many human MHC-II (DR) alleles and we estimate that we can interrogate >85% of all samples using 17 different tetramers and dextramers. In collaboration with core D, we propose to correlate the number and phenotype of ApoB-specific CD4 T cells with subclinical CVD as defined by coronary calcium (CAC) scores and CAC score progression. Project 4 will collaborate with project 1 on antigen presentation by monocytes and intravital microscopy, project 2 on the importance of LDL modifications and project 3 on studying the B1 cell response to LDL. When the proposed work is completed, we will understand the role of ApoB-specific CD4 T cells in modulating atherosclerosis by IL-10. The mechanistic mouse work provides the basis for testing the relevance of ApoB-specific CD4 T cells in CVD patients. ApoB-specific CD4 T cells are likely useful immunological biomarkers in atherosclerosis and the results can guide future therapeutic and preventive efforts.
Project 4 narrative Atherosclerosis or hardening of the arteries is the #1 killer world-wide, killing more people than all cancers combined. The arteries do not harden everywhere, but there are hot spots that can become inflamed and then become vulnerable to rupture. If rupture happens, the artery is occluded and a heart attack or stroke ensues with the known, often catastrophic consequences. The inflammation in the arteries is regulated by the immune system. The healthy immune system keeps the disease in check by providing anti-inflammatory mediators, almost like the body's own aspirin. We have evidence in mice that these mechanisms fail over time and hardening of the arteries gets much worse as the mice age. Here, we will test the importance of this proposed mechanism by testing bankedfrozen blood cells from almost 1000 subjects with and without cardiovascular disease. The results will likely provide useful biomarkers that can be used to test the severity of the disease by a simple blood test. They may also guide future efforts in prevention and treatment of this disease.
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