Endothelial cell costimulation of T cell activation through CD58-CD2 interactions involves lipid raft aggregation

Human endothelial cells (EC) costimulate CD4(+) memory T cell activation th rough CD58-CD2 interactions. In this study we tested the hypothesis that EC activate distinct costimulatory pathways in T cells that target specific t ranscription factors. AP-1, composed of fos and jun proteins, is a critical effector of TCR signaling and binds several sites in the IL-2 promoter. EC augment c-fos promoter activity in T cells; however, deletion analysis rev eals no transcription factor binding sites in the promoter uniquely respons ive to EC costimulation. Overexpression of AP-1 proteins in T cells augment s the activity of an AP-1-luciferase reporter gene equally in the absence o r the presence of EC costimulation. Interestingly, EC stimulate a similar 2 - to 3-fold up-regulation of AP-1, NF-AT, NF-kappaB, and NF-IL-2-luciferase reporters. CD2 mAbs completely block EC effects on all of these pathways, as well as costimulation of IL-2 secretion. We conclude that EC costimulati on through CD2 does not trigger a single distinct costimulatory pathway in T cells, but rather, it amplifies several pathways downstream of the TCR. I ndeed, we find that early EC costimulation acts "upstream" of the TCR by pr omoting lipid raft aggregation, thus amplifying TCR signaling. Soluble CD2 mAbs block EC-induced raft aggregation, whereas cross-linking CD2 promotes aggregation. These data are consistent with the critical role of CD2 in org anizing the T cell-APC contact zone.