Differential effect of the activation of protein kinase A on the protein synthesis and secretion in the T-helper 2 cell line D10.G4.1

Beta-agonists modulate T-cell functions via direct actions on type 1 and type 2 cells

Although the beta2-adrenergic receptor (beta2AR) is the most extensively characterized G-protein-coupled receptor (GPCR), the effects of beta-agonists on T-cell subtype function remain poorly understood. In contrast to studies suggesting lack of beta2AR expression on type 2 T cells, we demonstrate that type 2 interleukin-13+ (IL-13+) T cells (CD4+ or CD8+) in human peripheral blood lymphocytes (PBLs) can respond directly to beta-agonist, with effects including induction of protein kinase A (PKA) activity and associated inhibition of CD3-stimulated CD25 expression; CD3-stimulated IL-13, interferon-gamma (IFN-gamma), and IL-2 production; and p38 mitogen-activated protein kinase (MAPK) phosphorylation. PGE2 was more efficacious than beta-agonist in activating PKA and inhibiting cytokine production. beta-agonist and PGE2 also inhibited phorbol myristate acetate (PMA) + calcimycin-stimulated IFN-gamma and IL-2 (but not IL-13) production, suggesting that upstream CD3-initiated signaling is not the sole locus of PKA actions. Differential regulation of PMA-stimulated p38, p42/p44, and NF-kappaB explained the capacity of PGE2 and beta-agonist to inhibit IFN-gamma but not IL-13 production. The inhibition of CD3 + CD28-stimulated IL-13 production by both beta-agonist and PGE2 was reversed at low agonist concentrations, resulting in enhanced IL-13, but not IFN-gamma or IL-2, production. These findings identify direct effects of beta2AR activation on T-cell subtypes and suggest a complex role for GPCRs and PKA activity in modulating T-cell functions.

Morphine Induces CD4+ T Cell IL-4 Expression through an Adenylyl Cyclase Mechanism Independent of the Protein Kinase A Pathway

Impaired host defense mechanisms after major operative procedures and trauma are recognized as important factors in the development of infectious complication. Trauma is associated with impaired cellular immunity and CD4+ T cell Th2 differentiation. We have previously implicated morphine treatment as a possible mechanism for Th2 differentiation after injury. In this investigation we first establish that morphine treatment in vivo results in Th2 differentiation and that this effect is mediated through a naltrexone-sensitive opioid receptor. We investigated the intracellular mechanism by which morphine controls CD4+ T cell differentiation and demonstrate that morphine treatment in vitro 1) increases anti CD3/CD28 Ab-induced CD4+ T cell IL-4 protein synthesis, IL-4 mRNA, and GATA-3 mRNA accumulation through a pertussis toxin-sensitive receptor; 2) results in a dose-dependent increase in anti-CD3/CD28 Ab-induced CD4+ T cell cytoplasmic cAMP concentration; and 3) increases the forskolin-stimulated cytoplasmic cAMP level through a pertussis toxin-sensitive receptor. We also demonstrate that chronic morphine treatment increases anti-CD3/CD28 Ab-induced IL-4 promoter activity and IL-4 immunoprotein expression through a p38 MAPK-dependent, but protein kinase A- and Erk1/Erk2-independent, mechanism.

Effects of histamine on Th1/Th2 cytokine balance

Atopic asthma is a chronic inflammatory disorder of the airways where upon exposure to allergens, the body mounts an immune response. This disease is associated with an increase in the number of Th2 (T helper type 2) cells and Th2 cytokines and a decrease in the number of Th1 (T helper type 1) cells and Th1 cytokines. Histamine plays an important role in the pathogenesis of atopic asthma through differential regulation of T helper lymphocytes. Histamine enhances the secretion of Th2 cytokines such as IL-4 (interleukin-4), IL-5, IL-10 and IL-13 and inhibits the production of Th1 cytokines IL-2 and IFNgamma (interferon-gamma) and monokine IL-12. It has been shown that histamine can modulate the cytokine network through upregulation of PGE(2) (prostaglandin E(2)) and NO (nitric oxide). Histamine also affects cytokine production via H2 receptors and through the activation of PKA (protein kinase A). We have also demonstrated that the Jak-STAT (Janus kinase-signal transducers and activators of transcription) pathway is involved in histamine-mediated regulation of Th2 cytokines IL-5, IL-10, IL-13 and Th1 cytokine IFNgamma. While standard treatment of asthma consists of beta-receptor agonists and inhaled corticosteroids, the elucidation of histamine's control over the cytokine network and the Th1/Th2 balance provides a basis for the potential use of antihistamines in the prevention and treatment of atopic asthma. Several other anti-allergic agents to modulate the Th1/Th2 balance are under current investigation based on this paradigm. These include cytokines, cytokine antagonists, anti-IgE, and vaccinations. As more advances are made in our understanding of histamine and its control over the Th1/Th2 balance, the use of new therapeutic targets such as these will play a prominent role in disease management.

Regulation of IL-13 production by histamine in cloned murine T helper type 2 cells

Histamine affects the balance of T helper type 1 (Th1) and T helper type 2 (Th2) cytokines by shifting cytokine production from a Th1 to a Th2 pattern. Interleukin-13 (IL-13) is an important autacoid mediator that has been implicated in the development of allergic disease. This study was designed to investigate the mechanisms of regulation of IL-13 by histamine in Th2 cells. D10.G4.1 cells, a murine Th2 cell line, were treated with histamine (10(-8)-10(-4) M) and then activated with PMA (phorbol 12 myristate 13-acetate) plus ionomycin or alphaCD3. Levels of IL-13 production were then measured by enzyme-linked immunosorbent assay (ELISA) and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Cells were pretreated with histamine receptor antagonists pyrilamine, ranitidine, cimetidine and thioperamide to determine the involvement of histamine receptors. Cells were also pretreated with protein kinase A (PKA) inhibitors N-[2-(methylaminoethyl)]-5-isoquinoline-sulfonamide (H-8) and Rp-diastereomer of adenosine cyclic 3'5'-phosphorothionate (Rp-cAMPS), and Janus kinase-signal transducer and activator of transcription (Jak-STAT) inhibitor tyrphostin AG490 prior to the addition of histamine. H-8 is an inhibitor of the catalytic subunit of PKA while Rp-cAMPS is an inhibitor of the regulatory subunit of PKA. Tyrphostin is an inhibitor of Jak2, Jak3, STATI, STAT3 and STAT5. Finally, cells were pretreated with IL-12, a monokine known to repress STAT6 DNA binding. We found that histamine dose-dependently enhanced IL-13 secretion and mRNA levels in Th2 cells via H1 and H2 receptors. Pretreatment of cells with H-8, Rp-cAMPS and tyrphostin prevented histamine-induced secretion and transcription of IL-13. Likewise, pretreatment of Th2 cells with IL-12 also reversed histamine's effects on IL-13 secretion from stimulatory to inhibitory. These observations suggest a role for PKA and the Jak-STAT pathway in histamine-mediated elevation of IL-13 secretion and transcription.