Deficiency of lymphocyte activation gene-3 (LAG3) is significantly associated with increased cardiovascular disease risk with in vitro results demonstrating increased TNF-α and decreased IL-10 secretion from LAG3-deficient human B lymphoblasts. The hypothesis tested in this study was that Lag3 deficiency in dendritic cells (DCs) would significantly affect cytokine expression, alter cellular metabolism, and prime naive T cells to greater effector differentiation. Experimental approaches used included differentiation of murine bone marrow–derived DCs (BMDCs) to measure secreted cytokines, cellular metabolism, RNA sequencing, whole cell proteomics, adoptive OT-II CD4+Lag3+/+ donor cells into wild-type (WT) C57BL/6 and Lag3−/− recipient mice, and ex vivo measurements of IFN-γ from cultured splenocytes. Results showed that Lag3−/− BMDCs secreted more TNF-α, were more glycolytic, used fewer fatty acids for mitochondrial respiration, and glycolysis was significantly reduced by exogenous IL-10 treatment. Under basal conditions, RNA sequencing revealed increased expression of CD40 and CD86 and other cytokine-signaling targets as compared with WT. Whole cell proteomics identified a significant number of proteins up- and downregulated in Lag3−/− BMDCs, with significant differences noted in exogenous IL-10 responsiveness compared with WT cells. Ex vivo, IFN-γ expression was significantly higher in Lag3−/− mice as compared with WT. With in vivo adoptive T cell and in vitro BMDC:T coculture experiments, Lag3−/− BMDCs showed greater T cell effector differentiation and proliferation, respectively, compared with WT BMDCs. In conclusion, Lag3 deficiency in DCs is associated with an inflammatory phenotype that provides a plausible mechanism for increased cardiovascular disease risk in humans with LAG3 deficiency.

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