Regulation of signal transduction through the T cell antigen receptor

T cell signaling and autoimmune diabetes

Stimulation of the T-cell lymphocyte surface receptor (TCR) initiates a cascade of intracellular signaling events leading to proliferation, anergy, cytokine secretion, or apoptosis. In prediabetic NOD mice, T cell proliferative hyporesponsiveness has been correlated to decreased TCR-mediated signal transduction along the PKC/p21ras/p42mapk pathway. Limited data regarding T cell signaling defects are available in patients with autoimmune diabetes mellitus. Some but not all investigators have found decreased in vitro proliferative hyporesponsiveness to lectin mitogens or anti-CD3 mAb associated with impaired PKC activation and cytokine production. More recently, defective expression and function of the p21ras cascade was reported in these patients. Taken together, these data suggest that lymphocytes from animals and patients with autoimmune diabetes have defective TCR mediated signaling which may result in aberrant T cell activation and proliferation. This may lead to an imbalance of Th1/Th2 cytokine secretory pattern and thereby promote disease development.

TNP-470, a potent angiogenesis inhibitor, amplifies human T lymphocyte activation through an induction of nuclear factor-kappaB, nuclear factor-AT, and activation protein-1 transcription factors

TNP-470, an angiogenesis inhibitor derived from fumagillin, is foreseen as a promising anti-cancer drug. Its effectiveness to restrain tumor growth and its lack of major side effects have been demonstrated in several animal models and have led the drug to reach phase III clinical trials. Beside its antiangiogenesis activities, TNP-470 exhibits several effects on the immune system. We had shown previously that TNP-470 stimulated B lymphocyte proliferation through an action on T cells. In this study, we examined the cellular and molecular modifications induced by TNP-470 in normal human T lymphocytes. Transmission electron microscopic examination of PHA/TNP-470-treated T cells revealed significant morphologic modifications when compared with PHA-treated control T cells. TNP-470 induced indeed an important and significant increase of the nuclear size as well as major nuclear chromatin decondensation. This observation indicated that TNP-470 amplified T-cell activation and led us to investigate its effects on the activation of transcription factors involved in T-cell activation. Using electrophoretic mobility shift assays, we have demonstrated that TNP-470 amplifies and extends the DNA-binding activity of nuclear factor-AT, nuclear factor-KB, and activation protein-1 in T cells. Furthermore, the angioinhibin significantly increased the secretion of IL-2 and IL-4. Our data demonstrate that TNP-470 amplifies the activation of T cells. This effect, whose molecular mechanisms remain to be elucidated, has to be taken into account in the assessment of the antitumor effect of the drug.

The dynamics of T cell receptor signaling: complex orchestration and the key roles of tempo and cooperation

T cells constantly sample their environment using receptors (TCR) that possess both a germline-encoded low affinity for major histocompatibility complex (MHC) molecules and a highly diverse set of CDR3 regions contributing to a range of affinities for specific peptides bound to these MHC molecules. The decision of a T cell "to sense and to respond" with proliferation and effector activity rather than "to sense, live on, but not respond" is dependent on TCR interaction with a low number of specific foreign peptide:MHC molecule complexes recognized simultaneously with abundant self peptide-containing complexes. Interaction with self-complexes alone, on the other hand, generates a signal for survival without a full activation response. Current models for how this distinction is achieved are largely based on translating differences in receptor affinity for foreign versus self ligands into intracellular signals that differ in quality, intensity, and/or duration. A variety of rate-dependent mechanisms involving assembly of molecular oligomers and enzymatic modification of proteins underlie this differential signaling. Recent advances have been made in measuring TCR:ligand interactions, in understanding the biochemical origin of distinct proximal and distal signaling events resulting from TCR binding to various ligands, and in appreciating the role of feedback pathways. This new information can be synthesized into a model of how self and foreign ligand recognition each evoke the proper responses from T cells, how these two classes of signaling events interact, and how pathologic responses may arise as a result of the underlying properties of the system. The principles of signal spreading and stochastic resonance incorporated into this model reveal a striking similarity in mechanisms of decision-making among T cells, neurons, and bacteria.