Browsing by Subject "Treg"

Understanding the mechanisms that control T cell function and differentiation is crucial to develop new strategies to modulate immune function and prevent autoimmune and inflammatory disease. The balance between effector (Teff; Th1, Th2 and Th17) and regulatory (Treg) T cells is critical to provide an appropriate, but not excessive, immune response and therapies to induce Treg or inhibit Teff are likely promising treatment strategies. It has recently become clear that T cell metabolism is important in both T cell activation and differentiation. T cells undergo a metabolic reprogramming upon activation and not all differentiated T cell subsets utilize the same metabolic fuels or programs.

These metabolic differences are not trivial, as T cell metabolism is tightly

regulated and dysregulation can lead to cell death or reduced immunity. An

understanding of the metabolic differences between Teff and Treg may lead to a new direction for treating inflammatory diseases by modulating the Teff:Treg balance through metabolic inhibition. Previous studies have shown that Teff express higher levels of the glucose transporter Glut1 than Treg, however the role of Glut1, and importantly, the cell-intrinsic role of glucose metabolism in T cell differentiation and inflammation was not previously examined. The work presented here examines the role of Glut1 in T cell differentiation. We show that effector CD4 T cells were dependent on Glut1 for proliferation and function both in vitro and in vivo. In contrast, Treg were Glut1-independent and capable of suppressing colitis in the absence of Glut1 expression.

Additionally, previous studies have shown broad metabolic differences between Teff and Treg, however the specific metabolic profiles of Teff and Treg are poorly understood. Here, Teff and Treg metabolism is examined to test if dependence on distinct metabolic pathways will allow selective targeting of different T cell populations. We show that pyruvate dehydrogenase kinase 1 (PDHK1) is differentially expressed in the T cell subsets and inhibition of PDHK1 selectively suppresses Th17 and promotes Treg differentiation and function. Because Teff and Treg have distinct metabolic profiles, we hypothesized that the Treg-­specific transcription factor FoxP3 may drive the Treg oxidative metabolic program. We therefore examined the role of FoxP3 in T cell metabolism and determined that FoxP3 promotes glucose and lipid oxidation and suppresses glycolytic metabolism. Importantly, we show that promoting glycolysis with transgenic expression of Glut1 inhibits Treg suppressive capacity. Together, these data suggest that FoxP3 drives an oxidative metabolic program that is critical to Treg function. Overall, this work examines the metabolic phenotypes and regulation of Teff and Treg and potential metabolic targets that could be used to treat autoimmune and inflammatory disease.

LAT (linker for activation of T cells) is an important transmembrane adaptor protein in TCR-mediated signaling. Upon TCR engagement, LAT associates with multiple proteins which allows for the activation of downstream signaling pathways. The interaction between LAT with phospholipase C (PLC-gamma1) is especially critical for T cell receptor (TCR)-mediated Ca2+ signaling and MAPK activation. Knock-in mice harboring a mutation at the PLC-gamma1 binding site (Y136) of LAT develop a severe lymphoproliferative syndrome. These mice have defective thymic development and selection and lack natural regulatory T cells, implicating a breakdown of both central and peripheral tolerance. The phenotype observed in LAT-/- mice is even more severe.T cells are absent in the periphery of these mice due to a complete block in thymocyte development at the DN3 stage thereby making it difficult to study the physiological role of LAT in the activation and function of mature T cells. In order to bypass the developmental defects exhibited by LAT-/- and LATY136F mice, we developed conditional knock-in lines in which only a nonfunctional (ERCreLATf/-) or a LATY136F-mutated allele (ERCreLATf/m) of LAT is expressed in mature T cells after deletion of the wildtype LAT allele.

Analysis of ERCreLATf/m T cells after LAT deletion indicated that the interaction between LAT and PLC-gamma1 plays an important role in TCR-mediated signaling, proliferation, and IL-2 production. Furthermore, the deletion of LAT induced the development of the LATY136F lymphoproliferative syndrome in these mice. Although Foxp3+ natural Treg cells were present in these mice after deletion, they were unable to suppress the proliferation of conventional T cells. Our data indicated that the binding of LAT to PLC-gamma1 is essential for the suppressive function of CD4+CD25+ regulatory T cells.

We have also performed studies using ERCreLATf/- T cells to demonstrate that total LAT deficiency reduced the expression of Foxp3, CTLA4, and CD25 in peripheral Treg cells. Interestingly, mice with LAT deleted in peripheral T cells developed a lymphoproliferative syndrome similar to that observed in LATY136F mice although the disease caused by the LATY136F mutation was more severe. These data implicate LAT in both the positive and the negative regulation of mature T cells. Moreover, our findings indicate that LAT is essential in the maintenance of the regulatory T cell profile in the periphery, thereby aiding in the prevention of lymphoproliferative autoimmune disease.