| T cells are leaders of the body's defense against infections and malignancy; while normally contributing to beneficial immune responses, abnormal T cell activation may also contribute to autoimmune disease. An underlying component of T cell activation in both health and disease is the T cell: antigen presenting cell (APC) interaction. This interaction contributes to the formation of an immune synapse (IS), defined molecularly by the accumulation of signaling molecules, adhesive molecules, and the actin cytoskeleton at the site of T cell:APC contact.;Previous work has shown that the αLβ2 integrin, LFA-1, is required for T cell:APC adhesion and T cell proliferation. Talin directly interacts with the β2 cytoplasmic tail to increase its affinity for ligand. However, regulation of talin and its influences on T cell activation remain unknown. Using conditional knockout mice, we show that talin is required for the formation of stable T cell:APC contacts and contact dependent proliferation and cytokine production. In contrast to previous models, we find that talin is not required for LFA-1 clustering but is required for actin polarization to the IS.;To better understand regulation of talin-integrin contacts in T cells, we turned to the fibroblast literature. In the work described herein, the affects of four known integrin regulators, including calpain, PIPKIγ90, talin and Focal Adhesion Kinase (FAK) on T cell adhesion and activation are characterized. Calpain is required for integrin dependent migration in fibroblasts; however, it is dispensable for T cell adhesion and proliferation. PIPKIγ90 directly binds talin at a site overlapping talin's integrin binding site and produces PI(4,5)P2, which promotes talin-integrin interactions. We find that PIPKIγ90 negatively regulates T cell:APC contacts and proliferation, likely through direct interactions with talin. FAK is a signaling scaffold proposed to regulate talin's interactions with PIPKIγ90. Using a small molecule inhibitor, we find FAK is required for T cell:APC contacts and T cell proliferation. In this work, we identify novel positive and negative regulators of T cell integrin activation and correlate this with changes in T cell activation. Importantly, we find that integrin regulation in T cells differs from other systems. |
