Project Summary/Abstract This proposal intends to characterize Tfh cells, a population that is critical for disease development and maintenance in SLE and test the novel hypothesis that SLE-Tfh are uniquely sensitive to metabolic inhibition, a feature that can be exploited to therapeutic intervention. The scientific premise of this proposal is based on three lines of evidence: 1. The necessary role of Tfh cells for the production of pathogenic autoAbs in lupus has been well-established in SLE patients and mouse models; 2. Tfh cells induced by immunization are metabolically quiescent, a fact that we have confirmed showing that they are not affected by glucose inhibitors in lupus-prone and control mice; and 3. We have strong preliminary data showing that SLE-Tfh cells from four different mouse models of lupus are sensitive to glucose. We propose the hypothesis that spontaneous Tfh cells supporting the production of autoAbs (SLE-Tfh) have a different metabolism than Tfh cells providing protective humoral immunity against pathogens (TD-Tfh) in either lupus or normal mice. Based on similarities of CD4+ T cell functions and metabolism in lupus-prone mice and SLE patients, we also hypothesize that the expanded Tfh cells in SLE patients also have a different metabolism than that of health controls (HCs). Consequently, we predict that targeting Tfh cellular metabolism provides an effective approach to treat lupus without compromising the patients’ protection against TD- pathogens. We propose to test these hypotheses using cellular and molecular immunology approaches in mouse models as well as with human PBLs with the three following specific aims 1. To define the molecular and metabolic signatures of SLE-Tfh as compared to TD-Tfh cells elicited by TD-dependent Ags (PR8 flu virus and NP-OVA) in lupus mice and B6 controls. The immunophenotypes, anatomical location, gene expression, and metabolic profile of spontaneous Tfh cells in TC and B6.lpr mice will be compared to that of flu-specific I-A(b) NP-tetramer positive Tfh cells in TC, B6.lpr and B6 mice infected with PR8 virus. In addition to these polyclonal T cell models, we will use an adoptive transfer model of OVA-specific OT-II T cells carrying the Sle1 lupus susceptibility allele that favors the expansion of Tfh cells (9) into NP-OVA immunized mice (10). This aim will define the functional differences between TD-Tfh and SLE-Tfh cells in two models of lupus and with two different TD-immunizations. 2. To define the response of SLE-Tfh and TD-Tfh cells to glucose inhibition in the mouse. Using the same experimental systems as in SA1, we will compare the responses of SLE-Tfh cells and TD-Tfh cells to glucose inhibition in mice treated with 2DG, a glucose analog that blocks the first reaction of glycolysis. 3. To compare the molecular and metabolic signatures of circulating cTfh cells in SLE patients and HCs, as well as their response to metformin. We hypothesize that the expansion of cTfh cells in SLE pat...