Abstract 87: Sterol-Mediated Regulation of γδ T Lymphocytes

Abstract

Objective: gammadelta (γδ) T lymphocytes, which bridge innate and adaptive immunity, may be differentially regulated by cholesterol and play distinct roles from the conventional alphabeta (αβ) subset in the development of atherosclerosis. γδ T cells represent a small subset of total T cells (∼ 3-5% of CD3+ cells). These cells express unique γδ T cell receptors, and recognize lipid and peptide antigens without processing and presentation by MHC molecules. γδ T cells react much faster toward pathogen invasion than αβ T cells, and thus are considered one of the first lines of immune defense. Methods: αβ and γδ T lymphocytes from mice were evaluated for their lipid content, gene expression, proliferation, apoptosis, and activation. Results and conclusion: Nile Red staining revealed higher intracellular lipid content in γδ T cells, comparing to the αβ subset (1.3 folds of αβ, p<0.05; n=5). We therefore hypothesize that the basal higher sterol content elicits the turnover and activation of γδ T lymphocytes for rapid response. We found that genes involved in cholesterol esterification (ACAT1 and ACAT2) and efflux (ABCA1) are upregulated in γδ cells compared to conventional αβ T cells. PCSK9, which downregulates LDLR posttranslationally, is elevated in γδ T cells, suggesting cholesterol metabolism is differentially regulated in the two subsets. BrdU incorporation and annexin V staining revealed significantly higher proliferative (3.4 folds of αβ, p<0.001; n=8) and apoptotic (34.9 folds of αβ, p<0.001; n=6) rates of γδ T cells in vivo, suggesting a higher turnover rate of the γδ subset. Staining for ganglioside GM1 showed elevated lipid raft levels in γδ T cells (1.9 folds of αβ, p<0.001; n=8), implying enhanced TCR signaling and activation. Notably, the percentages of total (2.3 folds of αβ, p<0.01; n=3) and pro-inflammatory cytokine IL-17- producing (3.9 folds of αβ, p<0.01; n=4-5) γδ T cells increase in ApoE -/- mice fed a high cholesterol, high fat diet, implying a high sterol/high fat environment may promote γδ T cells activation in vivo. Taken together, our data suggest γδ T cells are more sensitive to cholesterol, and a high sterol environment may enhance γδ T cell turnover and activation in vivo.