Activated T helper 1 and T helper 2 cells differentially express the beta-2-adrenergic receptor: a mechanism for selective modulation of T helper 1 cell cytokine production.

Abstract We recently reported that resting clones of murine Th1 cells, but not resting Th2 cells, expressed a detectable level of the beta-2-adrenergic receptor (beta 2AR). In the present study, we proposed that the level of beta 2AR expression on anti-CD3 mAb-activated CD4+ effector Th cells may differ from the level on resting cells, and that a change in receptor expression may alter the functional responsiveness of these cells to either the beta 2AR-selective ligand terbutaline or the sympathetic neurotransmitter norepinephrine. Following anti-CD3 activation, the beta 2AR was expressed on Th1 cells, but not Th2 cells. The number of binding sites on Th1 cells was maintained, with no change in affinity, over a 24-h activation period. When Th clones were exposed to terbutaline following anti-CD3 activation, Th1 cell, but not Th2 cell, cytokine production was modulated. IL-2 production by Th1 cells was decreased, while IFN-gamma production was not significantly altered. The decrease in IL-2 production was concentration dependent and was blocked by an antagonist. In comparison with control supernatants, the lower level of IL-2 present in terbutaline-exposed culture supernatants supported the proliferation of an IL-2-dependent Th1 clone to a lesser degree. Additionally, norepinephrine down-modulates IL-2, but not IFN-gamma, production by binding specifically to the beta-adrenergic receptor. Thus, a detectable level of the beta 2AR is expressed on activated Th1 cells, but not activated Th2 cells, thereby providing a mechanism by which IL-2 production is preferentially modulated by an endogenous and therapeutic ligand following Th1 cell activation.</jats:p

Differential expression of the beta2-adrenergic receptor by Th1 and Th2 clones: implications for cytokine production and B cell help.

Abstract An important function of the sympathetic nervous system is to maintain homeostasis by modulating the level of cellular activity in many diverse organ systems. The sympathetic neurotransmitter norepinephrine modulates the level of T and B lymphocyte activity by binding to the beta2-adrenergic receptor (beta2AR). The present study was designed to elucidate the mechanism by which stimulation of the beta2AR affects both Th1/Th2 cell cytokine production and Th1/Th2 cell-dependent Ab production. Clones of murine Th1/Th2 cells were exposed to the beta2AR agonist terbutaline before activation by Ag-presenting B cells. Terbutaline exposure of Th1 cells before activation inhibited IFN-gamma production by Th1 cells and subsequent IgG2a production by B cells. IgG2a inhibition was prevented by addition of the betaAR antagonist nadolol or exogenous IFN-gamma. In contrast to Th1 cells, terbutaline did not affect either IL-4 production by Th2 cells or subsequent IgG1 production by B cells. Although baseline levels of intracellular cAMP were similar in both subsets, terbutaline induced an increase in cAMP levels in Th1 cells only. Radioligand binding studies showed that a detectable number of beta2AR binding sites were present on Th1 cells, but not on Th2 cells. Immunofluorescence analyses showed that Th1 cells expressed a higher level of the beta2AR cytoplasmic carboxyl terminus than did Th2 cells. These results show that expression of the beta2AR binding site by Th1 cells, but not by Th2 cells, establishes a physiologic mechanism for selective modulation of Th1 cell IFN-gamma production and IFN-gamma-dependent IgG2a production, provided that beta2AR stimulation occurs before cell activation by a B cell.</jats:p

Direct AFM Observation of Strain Effects on MOCVD-Grown GaN Epilayer Surface Morphology

ABSTRACTIn this study, we investigate the dependence of GaN surface morphology on the absolute strain values for thin (&lt;10 μm) epitaxial films grown by MOCVD on c-plane sapphire substrates of various miscut angles towards the m-plane. Results indicate an excellent correlation between the surface roughness observed employing an AFM tool and epilayer strain values. An overall increase of surface roughness (decrease of atomic terrace width) is found with decreasing compressive strain (epilayer vs. bulk value). In addition, sapphire substrates with increasing miscut angle (0.30 deg) appear to relax the inherent, built-in strain differently in the vertical (growth) direction when compared to just (0.00 deg) substrates. Strain relaxation by typical V-shaped, hexagonal pits is directly imaged through the comparison of surface features inside and outside of pits in the thin GaN epilayer films.</jats:p

Mitochondrial Superoxide Signaling Contributes to Norepinephrine-Mediated T-Lymphocyte Cytokine Profiles

<div><p>Norepinephrine (NE) produces multifaceted regulatory patterns in T-lymphocytes. Recently, we have shown that NE utilizes redox signaling as evidenced by increased superoxide (O₂^●-) causally linked to the observed changes in these cells; however, the source of this reactive oxygen species (ROS) remains elusive. Herein, we hypothesized that the source of increased O₂^●- in NE-stimulated T-lymphocytes is due to disruption of mitochondrial bioenergetics. To address this hypothesis, we utilized purified mouse splenic CD4+ and CD8+ T-lymphocytes stimulated with NE and assessed O₂^●- levels, mitochondrial metabolism, cellular proliferation, and cytokine profiles. We demonstrate that the increase in O₂^●- levels in response to NE is time-dependent and occurs at later points of T-lymphocyte activation. Moreover, the source of O₂^●- was indeed the mitochondria as evidenced by enhanced MitoSOX Red oxidation as well as abrogation of this signal by the addition of the mitochondrial-targeted O₂^●--scavenging antioxidant MitoTempol. NE-stimulated T-lymphocytes also demonstrated decreased mitochondrial respiratory capacity, which suggests disruption of mitochondrial metabolism and the potential source of increased mitochondrial O₂^●-. The effects of NE in regards to redox signaling appear to be adrenergic receptor-dependent as specific receptor antagonists could reverse the increase in O₂^●-; however, differential receptors regulating these processes were observed in CD4+ versus CD8+ T-lymphocytes. Finally, mitochondrial O₂^●- was shown to be mechanistic to the NE-mediated T-lymphocyte phenotype as supplementation of MitoTempol could reverse specific changes in cytokine expression observed with NE treatment. Overall, these studies indicate that mitochondrial metabolism and O₂^●--mediated redox signaling play a regulatory role in the T-lymphocyte response to NE.</p></div