Increased ß2-adrenoceptor phosphorylation in airway smooth muscle in severe asthma: possible role of mast cell-derived growth factors.

The purpose of this study was to investigate whether growth factors produced by activated human lung mast cells (HLMCs) impair ß2 -adrenoceptor (ß2 -AR) function in human airway smooth muscle (ASM) cells. Protein array analysis confirmed the presence of various growth factors, including transforming growth factor (TGF)-ß1, in the supernatants of high-affinity IgE receptor (FcεRI)-activated HLMCs which, when applied to ASM cells, impaired albuterol-induced cyclic adenosine monophosphate (cAMP) production, an effect that was prevented following neutralization of TGF-ß1. This blunted ß2 -AR response was reproduced by treating ASM cells with TGF-ß1 or fibroblast growth factor (FGF)-2, which induced ß2 -AR phosphorylation at tyrosine residues Tyr141 and Tyr350 , and significantly reduced the maximal bronchorelaxant responses to isoproterenol in human precision cut lung slices (PCLS). Finally, ASM cells isolated from severe asthmatics displayed constitutive elevated ß2 -AR phosphorylation at both Tyr141 and Tyr350 and a reduced relaxant response to albuterol. This study shows for the first time that abnormal ß2 -AR phosphorylation/function in ASM cells that is induced rapidly by HLMC-derived growth factors, is present constitutively in cells from severe asthmatics.

Alternatives to connective tissue graft in the treatment of localized gingival recessions: A systematic review.

AIM: The aim of this Systematic Review (SR) was to assess the clinical efficacy of alternatives procedures; Acellular Dermal Matrix (ADM), Xenogeneic Collagen Matrix (XCM), Enamel Matrix Derivative (EMD) and Platelet Rich Fibrin (PRF), compared to conventional procedures in the treatment of localized gingival recessions. MATERIAL AND METHODS: Electronic searches were performed to identify randomized clinical trials (RCTs) on treatment of single gingival recession with at least 6 months of follow-up. Applying guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analyses statement (PRISMA). The risk of bias was assessed using the Cochrane Collaboration's Risk of Bias tool. RESULTS: Eighteen randomized controlled trials (RCTs) with a total of 390 treated patients (606 recessions) were included. This systematic review showed that: Coronally Advanced Flap (CAF) in conjunction with ADM was significantly better than CAF alone, while the comparison between CAF+ADM and CTG was affected by large uncertainty. The CAF+EMD was significantly better than CAF alone, whereas the comparison between CAF+EMD and CTG was affected by large uncertainty. No significant difference was recorded when comparing CAF+XCM with CAF alone, and the comparison between CAF+XCM and CTG was affected by large uncertainty. The comparison between PRF and others technique was affected by large uncertainty. CONCLUSION: ADM, XCM and EMD assisted to CAF might be considered alternatives of CTG in the treatment of Miller class I and II gingival recession.

Protein phosphatase 5 mediates corticosteroid insensitivity in airway smooth muscle in patients with severe asthma.

BACKGROUND: The mechanisms driving glucocorticoid (GC) insensitivity in patients with severe asthma are still unknown. Recent evidence suggests the existence of GC-insensitive pathways in airway smooth muscle (ASM) caused by a defect in GC receptor (GRα) function. We examined whether other mechanisms could potentially explain the reduced sensitivity of ASM cells to GC in severe asthmatics. METHODS: Airway smooth muscle cells from healthy and severe asthmatic subjects were treated with TNF-α and responses to corticosteroids in both cohorts were compared by ELISA, immunoblot, immunohistochemistry and real-time PCR. Immunohistochemistry and flow cytometry assays were used to assess the expression of the protein phosphatase PP5 in endobronchial biopsies and ASM cells. RESULTS: The production of CCL11 and CCL5 by TNF-α was insensitive to both fluticasone and dexamethasone in ASM cells from severe asthmatic compared to that in healthy subjects. Fluticasone-induced GRα nuclear translocation, phosphorylation at serine 211 and expression of GC-induced leucine zipper (GILZ) were significantly reduced in ASM cells from severe asthmatics compared to responses in healthy subjects. Levels of PP5 were increased in ASM cells from severe asthmatics and PP5 knockdown using siRNA restored fluticasone repressive action on chemokine production and its ability to induce GRα nuclear translocation and GRE-dependent GILZ expression. In vivo PP5 expression was also increased in the ASM bundles in endobronchial biopsies in severe asthmatics. CONCLUSIONS: PP5-dependent impairment of GRα function represents a novel mechanism driving GC insensitivity in ASM in severe asthma.

Abnormal corticosteroid signalling in airway smooth muscle: mechanisms and perspectives for the treatment of severe asthma.

Growing in vivo evidence supports the concept that airway smooth muscle produces various immunomodulatory factors that could contribute to asthma pathogenesis via the regulation of airway inflammation, airway narrowing and remodelling. Targeting ASM using bronchial thermoplasty has provided undeniable clinical benefits for patients with uncontrolled severe asthma who are refractory to glucocorticoid therapy. The present review will explain why the failure of glucocorticoids to adequately manage patients with severe asthma could derive from their inability to affect the immunomodulatory potential of ASM. We will support the view that ASM sensitivity to glucocorticoid therapy can be blunted in severe asthma and will describe some of the factors and mechanisms that could be responsible for glucocorticoid insensitivity.

IL-33 drives airway hyper-responsiveness through IL-13-mediated mast cell: airway smooth muscle crosstalk.

BACKGROUND: Mast cell localization within the airway smooth muscle (ASM)-bundle plays an important role in the development of airway hyper-responsiveness (AHR). Genomewide association studies implicate the 'alarmin' IL-33 in asthma, but its role in mast cell-ASM interactions is unknown. OBJECTIVES: We examined the expression and functional role of IL-33 in bronchial biopsies of patients with and without asthma, ex vivo ASM, mast cells, cocultured cells and in a mouse model system. METHODS: IL-33 protein expression was assessed in human bronchial tissue from 9 healthy controls, and 18 mild-to-moderate and 12 severe asthmatic patients by immunohistochemistry. IL-33 and ST2 mRNA and protein expression in human-derived ASM, epithelial and mast cells were assessed by qPCR, immunofluorescence and/or flow cytometry and ELISA. Functional assays were used to assess calcium signalling, wound repair, proliferation, apoptosis and contraction. AHR and inflammation were assessed in a mouse model. RESULTS: Bronchial epithelium and ASM expressed IL-33 with the latter in asthma correlating with AHR. ASM and mast cells expressed intracellular IL-33 and ST2. IL-33 stimulated mast cell IL-13 and histamine secretion independent of FcεR1 cross-linking and directly promoted ASM wound repair. Coculture of mast cells with ASM activated by IL-33 increased agonist-induced ASM contraction, and in vivo IL-33 induced AHR in a mouse cytokine installation model; both effects were IL-13 dependent. CONCLUSION: IL-33 directly promotes mast cell activation and ASM wound repair but indirectly promotes ASM contraction via upregulation of mast cell-derived IL-13. This suggests that IL-33 may present an important target to modulate mast cell-ASM crosstalk in asthma.

Ozone inhalation induces exacerbation of eosinophilic airway inflammation and hyperresponsiveness in allergen-sensitized mice.

BACKGROUND: Ozone (O(3)) exposure evokes asthma exacerbations by mechanisms that are poorly understood. We used a murine model to characterize the effects of O(3) on allergic airway inflammation and hyperresponsiveness and to identify factors that might contribute to the O(3)-induced exacerbation of asthma. METHODS: BALB/c mice were sensitized and challenged with Aspergillus fumigatus (Af). A group of sensitized and challenged mice was exposed to 3.0 ppm of O(3) for 2 h and studied 12 h later (96 h after Af challenge). Naive mice and mice exposed to O(3) alone were used as controls. Bronchoalveolar lavage (BAL) cellular and cytokine content, lung function [enhanced pause (P(enh))], isometric force generation by tracheal rings and gene and protein expression of Fas and FasL were assessed. Apoptosis of eosinophils was quantified by FACS. RESULTS: In sensitized mice allergen challenge induced a significant increase of P(enh) and contractile force in tracheal rings that peaked 24 h after challenge and resolved by 96 h. O(3) inhalation induced an exacerbation of airway hyperresponsiveness accompanied by recurrence of neutrophils and enhancement of eosinophils 96 h after allergen challenge. The combination of allergen and O(3) exposure inhibited Fas and FasL gene and protein expression and eosinophil apoptosis and increased interleukin-5 (IL-5), granulocyte-macrophage-colony stimulating factor (GM-CSF) and G-CSF protein levels. CONCLUSIONS: O(3) affects airway responsiveness of allergen-primed airways indirectly by increasing viability of eosinophils and eosinophil-mediated pathological changes.

Interferon-gamma modulates cysteinyl leukotriene receptor-1 expression and function in human airway myocytes.

Leukotrienes play a critical role in promoting bronchoconstriction in asthma. The purpose of this study was to examine whether interferon (IFN)-gamma, a cytokine upregulated in asthmatic airways, modulates leukotriene (LT)D4 receptor expression and contractile responses in cultured human airway smooth muscle (HASM) cells. Treatment of HASM cells with IFN-gamma (10 to 1,000 U/ml) stimulated a dose-dependent increase in cell-surface expression of cysteinyl leukotriene receptor 1 (CysLT1) as determined by flow cytometry. CysLT1 messenger RNA (mRNA) levels were also significantly enhanced by IFN-gamma, as demonstrated by reverse transcription-polymerase chain reaction. To determine the functional relevance of increased CysLT1 expression in HASM, cell stiffness responses to LTD4 were measured with magnetic twisting cytometry. IFN-gamma (1,000 U/ml for 24 h) markedly increased LTD4-induced changes in cell stiffness, from 4.6 +/- 1 [mean +/- SEM]% to 24.4 +/- 3.7% (n = 8, p < 0.05). Montelukast, a CysLT1 antagonist, completely inhibited LTD4-induced increases in cell stiffness. IFN-gamma had no effect on the cell stiffness responses to bradykinin, another contractile agonist. Collectively, these data suggest that IFN-gamma increases LTD4 responses in HASM cells by increasing cell-surface expression of CysLT1. Our data suggest that increased levels of IFN-gamma in asthmatic individuals may promote airway hyperresponsiveness and asthma exacerbations by directly modulating contractile responses of HASM.

Tumor necrosis factor receptor (TNFR) 1, but not TNFR2, mediates tumor necrosis factor-alpha-induced interleukin-6 and RANTES in human airway smooth muscle cells: role of p38 and p42/44 mitogen-activated protein kinases.

Little information is available regarding the mechanisms involved in cytokine-induced synthetic function of human airway smooth muscle (ASM) cells. Here, we report that tumor necrosis factor receptor (TNFR) 1-induced p38 and p42/44 mitogen-activated protein kinase (MAPK) activation modulates tumor necrosis factor-alpha (TNF alpha)-mediated synthetic responses: expression of intercellular adhesion molecule-1 (ICAM-1) and secretion of interleukin (IL)-6 and the regulated-on-activation, normal T-cell expressed and secreted (RANTES) chemokine in human ASM cells. Pretreatment of ASM cells with SB203580, a p38 MAPK inhibitor, slightly enhanced TNF alpha-induced ICAM-1 expression in a dose-dependent manner but partially inhibited secretion of RANTES and IL-6. In contrast, PD98059, a p42/44 inhibitor, reduced ICAM-1 expression by 50% but had no effect on TNF alpha-induced RANTES or IL-6 secretion. SB203580 and PD98059 had little effect on TNF alpha-induced nuclear factor-kappa B (NF-kappa B) activation as determined in cells transfected with a NF-kappa B-luciferase reporter construct. We also found that agonistic antibodies specific for either TNFR1 or TNFR2 stimulated IL-6 and RANTES secretion and activated p38 and p42/44 MAPKs. In addition, both antibodies induced NF-kappa B-mediated gene transcription. Using receptor-specific blocking antibodies, we found that TNFR1 primarily regulates TNF alpha-induced IL-6 and RANTES secretion and activation of p38 and p42/44 MAPK pathways. Interestingly, we found that TNFR1 and TNFR2 are expressed differently on the cell surface of ASM cells. Our data suggest that despite the presence of functional TNFR2, TNFR1 associated with MAPK-dependent and -independent pathways is the primary signaling pathway involved in TNF alpha-induced synthetic functions in ASM cells.

Tumor necrosis factor-alpha-induced secretion of RANTES and interleukin-6 from human airway smooth-muscle cells. Modulation by cyclic adenosine monophosphate.

Although 3':5' cyclic adenosine monophosphate (cAMP) is known to modulate cytokine production in a number of cell types, little information exists regarding cAMP-mediated effects on this synthetic function of human airway smooth-muscle (HASM) cells. We examined the effect of increasing intracellular cAMP concentration ([cAMP](i)) on tumor necrosis factor (TNF)-alpha-induced regulated on activation, normal T cells expressed and secreted (RANTES) and interleukin (IL)-6 secretion from cultured HASM cells. Pretreatment of HASM with prostaglandin (PG) E(2), forskolin, or dibutyryl cAMP inhibited TNF-alpha-induced RANTES secretion but increased TNF-alpha-induced IL-6 secretion. Moreover, stimulation with PGE(2), forskolin, or dibutyryl cAMP alone increased basal IL-6 secretion in a concentration-dependent manner. SB 207499, a specific phosphodiesterase type 4 inhibitor, augmented the inhibitory effects of PGE(2) and forskolin on TNF-alpha-induced RANTES. Collectively, these data demonstrate that increasing [cAMP](i) in HASM effectively increases IL-6 secretion but reduces RANTES secretion promoted by TNF-alpha. Reverse transcriptase/polymerase chain reaction and ribonuclease protection assays suggested that these opposite effects of increased [cAMP](i) on TNF-alpha- induced IL-6 and RANTES secretion may occur at the transcriptional level. Accordingly, we examined the effects of TNF- alpha and cAMP on the regulation of nuclear factor (NF)-kappaB, a transcription factor known to modulate cytokine synthesis in numerous cell types. Stimulation of HASM cells with TNF-alpha increased NF-kappaB DNA-binding activity. However, increased [cAMP](i) in HASM neither activated NF-kappaB nor altered TNF-alpha- induced NF-kappaB DNA-binding activity. These results were confirmed using a NF-kappaB-luciferase reporter assay. Together, our data suggest that TNF-alpha-induced IL-6 and RANTES secretion may be associated with NF-kappaB activation, and that inhibition of TNF-alpha-stimulated RANTES secretion and augmentation of IL-6 secretion by increased [cAMP](i) in HASM cells occurs via an NF-kappaB-independent mechanism.

[Cerebral hemodynamics in the syndrome of pseudomigraine with csf-pleocytosis:a transcranial doppler study]. / Hemodinámica cerebral en el síndrome de pseudomigraña con pleocitosis de LCR: un estudio Doppler transcraneal.

INTRODUCTION: The clinical picture of the pseudomigraine with CSF pleocytosis syndrome is of intermittent headaches, sometimes accompanied by episodes of transient neurological defects and lymphocyte pleocytosis, which occur for a variable length of time, followed by spontaneous resolution. It has been suggested that the cause is immunogenic due to post-infectious activation of the humoral immune system against the leptomeningeal vascular structures, but this hypothesis does not explain the accompanying transient deficit phenomena. MATERIAL AND METHODS: We present a study of cerebral hemodynamics using transcranial Doppler in a patient diagnosed as having pseudomigraine with pleocytosis according to current criteria. RESULTS: Our results suggest the presence of cerebral vascular instability and increased vascular reactivity to induced hypocapnia and hypercapnia, similar to that reported in patients with migraine with aura. At no time was significant increase in the average rate of cerebral blood flow detected, comparable to that usually seen in patients with bacterial or viral meningitis. CONCLUSIONS: Although the cause cannot be established, from our study it would seem that headache in the pseudomigraine with pleocytosis syndrome is related to cerebral vascular instability and therefore probably to activation of the trigeminal-vascular system. It is possible that the deficit phenomena may also have a similar explanation to that of patients with migraine with aura, that is, a propagated cortical depression. Transcranial Doppler studies may be useful in the diagnosis of pseudomigraine with pleocytosis syndrome.

Hemodinámica cerebral en el síndrome de pseudomigraña con pleocitosis de LCR: un estudio doppler transcraneal / Cerebral hemodynamics in the syndrome of pseudomigraine with CSF pleocytosis: a transcranial Doppler study

Introducción. El síndrome de pseudomigraña con pleocitosis (PMP) de LCR es un cuadro consistente en cefaleas intermitentes eventualmente acompañadas de episodios deficitarios neurológicos transitorios, junto con pleocitosis linfocitaria, que se suceden durante un período variable, con resolución espontánea .Se ha propuesto un origen inmunogénico por activación postinfecciosa del sistema inmune humoral frente a estructuras vasculares leptomeníngeas pero esta hipótesis no es capaz de explicar los fenómenos deficitarios transitorios acompañantes. Material y métodos. Presentamos un estudio de hemodinámica cerebral por Doppler transcraneal en un enfermo diagnosticado según los criterios vigentes de PMP. Resultados. Los resultados sugieren la existencia de una inestabilidad vascular cerebral y un aumento de la reactividad vascular ante hipocapnia e hipercapnia inducida, similar a la constatada en pacientes afectos de migraña con aura. No se detectó en ningún momento aumento significativo de las velocidades medias del flujo cerebral comparables a las habitualmente detectadas en pacientes con meningitis bacterianas o víricas. Conclusiones. Aunque no es posible establecer inferencias causales, nuestro estudio sugiere que la cefalea del síndrome PMP está relacionada con una inestabilidad vascular cerebral y, por lo tanto, probablemente con una activación del sistema trigémino-vascular. Es posible que los fenómenos deficitarios también tengan una explicación similar a la de los pacientes con migraña con aura, esto es, una depresión cortical propagada. Los estudios con Doppler transcraneal pueden ser útiles para el diagnóstico del síndrome de PMP (AU)

Activation of p55 tumor necrosis factor-alpha receptor-1 coupled to tumor necrosis factor receptor-associated factor 2 stimulates intercellular adhesion molecule-1 expression by modulating a thapsigargin-sensitive pathway in human tracheal smooth muscle cells.

Tumor necrosis factor-alpha (TNFalpha) stimulates the expression of intercellular adhesion molecule-1 (ICAM-1) by activating the transcription factor nuclear factor-kappaB (NF-kappaB) in human airway smooth muscle (ASM) cells. This study characterizes the receptor involved as well as critical downstream signaling events mediating cytokine-induced NF-kappaB activation and ICAM-1 expression. TNFalpha stimulation for 1 to 4 h induced ICAM-1 expression in human ASM cells. This rapid TNFalpha-induced ICAM-1 expression enhanced T-lymphocyte adhesion to ASM cells, which was inhibited by anti-ICAM-1 antibodies. Using immunostaining, we demonstrated that TNFalpha receptors TNFR1 and TNFR2 are expressed on native human tracheal smooth muscle. Treatment of cells with htr-9, an antibody that specifically activates TNFR1, also stimulated expression of ICAM-1 mRNA and protein. Utr-1, a blocking antibody to TNFR2, did not affect TNFalpha-mediated ICAM-1 expression. Both TNFalpha and htr-9 increased luciferase activity in ASM cells transfected with a NF-kappaB reporter plasmid. Overexpression of a dominant negative TNF receptor-associated factor 2 construct, lacking the NH(2)-terminal RING finger, completely abrogated both TNFalpha- and htr-9-mediated increases in NF-kappaB reporter activity. Thapsigargin, an agent that depletes intracellular calcium stores, abrogated both cytokine-mediated NF-kappaB-dependent ICAM-1 mRNA transcription and protein expression but had no effect on IkappaB degradation. In addition, chelating cytosolic calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid acetoxymethyl ester also inhibited cytokine TNFalpha-induced ICAM-1 expression. These data suggest that TNFR1, through a TNF receptor-associated factor 2-NF-kappaB signaling pathway, mediates TNFalpha-induced expression of ICAM-1 on ASM cells by involving a thapsigargin-sensitive signaling pathway.

Activation of tumor necrosis factor receptor 1 in airway smooth muscle: a potential pathway that modulates bronchial hyper-responsiveness in asthma?

The cellular and molecular mechanisms that are involved in airway hyper-responsiveness are unclear. Current studies suggest that tumor necrosis factor (TNF)-alpha, a cytokine that is produced in considerable quantities in asthmatic airways, may potentially be involved in the development of bronchial hyper-responsiveness by directly altering the contractile properties of the airway smooth muscle (ASM). The underlying mechanisms are not known, but growing evidence now suggests that most of the biologic effects of TNF-alpha on ASM are mediated by the p55 receptor or tumor necrosis factor receptor (TNFR)1. In addition, activation of TNFR1 coupled to the tumor necrosis factor receptor-associated factor (TRAF)2-nuclear factor-kappaB (NF-kappaB) pathway alters calcium homeostasis in ASM, which appears to be a new potential mechanism underlying ASM hyper-responsiveness.

Up-regulation of ICAM-1 by cytokines in human tracheal smooth muscle cells involves an NF-kappa B-dependent signaling pathway that is only partially sensitive to dexamethasone.

Although the precise mechanisms by which steroids mediate their therapeutic effects remain unknown, steroids have been reported to abrogate cytokine-induced activation of the transcription factor NF-kappa B. In some cell types, NF-kappa B activation is necessary to regulate cytokine-mediated cellular functions. However, compelling evidence suggests that the steroid inhibition of NF-kappa B is complex and cell specific. Using EMSA, we show that stimulation with TNF-alpha or IL-1 beta induces NF-kappa B DNA-binding activity in human airway smooth muscle cells. TNF-alpha and IL-1 beta also increased luciferase activity in airway smooth muscle cells transfected with a reporter plasmid containing kappa B enhancer elements. Cytokines activated NF-kappa B by rapidly degrading its cytosolic inhibitor I kappa B alpha, which was then regenerated after 60 min. Cytokine-mediated I kappa B alpha reappearance was completely blocked by the protein synthesis inhibitor cycloheximide. Inhibition of cytokine-mediated I kappa B alpha proteolysis using the protease inhibitors N-tosyl-L -phenylalanine chloromethyl ketone and N-acetyl-L -leucinyl-L -leucinyl-norleucinal also inhibited cytokine-mediated early expression of ICAM-1. Although dexamethasone partially inhibited IL-1 beta- and TNF-alpha-induced up-regulation of ICAM-1 at 4 h, dexamethasone had no effect on cytokine-induced ICAM-1 expression at 18-24 h. In addition, neither cytokine-induced degradation or resynthesis of I kappa B alpha nor NF-kappa B DNA-binding activity were affected by dexamethasone. In cells transfected with the luciferase reporter, dexamethasone did not affect TNF-alpha-induced NF-kappa B-dependent transcription. Interestingly, cytokine-mediated expression of cyclooxygenase-2 was completely abrogated by dexamethasone at 6 h. Together, these data demonstrate that cytokine-mediated NF-kappa B activation and ICAM-1 expression involve activation of a steroid-insensitive pathway.

Phosphatidylinositol 3-kinase mediates mitogen-induced human airway smooth muscle cell proliferation.

Hypertrophy and hyperplasia of airway smooth muscle (ASM) are important pathological features that contribute to airflow obstruction in chronic severe asthma. Despite considerable research effort, the cellular mechanisms that modulate ASM growth remain unknown. Recent evidence suggests that mitogen-induced activation of phosphoinositide (PI)-specific phospholipase C (PLC) and PI-dependent calcium mobilization are neither sufficient nor necessary to stimulate human ASM proliferation. In this study, we identify phosphatidylinositol (PtdIns) 3-kinase as a key regulator of human ASM proliferation. Pretreatment of human ASM with the PtdIns 3-kinase inhibitors wortmannin and LY-294002 significantly reduced thrombin- and epidermal growth factor (EGF)-induced DNA synthesis (IC(50) approximately 10 nM and approximately 3 microM, respectively). In separate experiments, wortmannin and LY-294002 markedly inhibited PtdIns 3-kinase and 70-kDa S6 protein kinase (pp70(S6k)) activation induced by stimulation of human ASM cells with EGF and thrombin but had no effect on EGF- and thrombin-induced p42/p44 mitogen-activated protein kinase (MAPK) activation. The specificity of wortmannin and LY-294002 was further suggested by the demonstrated inability of these compounds to alter thrombin-induced calcium transients, total PI hydrolysis, or basal cAMP levels. Transient expression of constitutively active PtdIns 3-kinase (p110*) activated pp70(S6k), whereas a dominant-negative PtdIns 3-kinase (Deltap85) blocked EGF- and thrombin-stimulated pp70(S6k) activity. Collectively, these data suggest that activation of PtdIns 3-kinase is required for the mitogenic effect of EGF and thrombin in human ASM cells. Further investigation of the role of PtdIns 3-kinase may offer new therapeutic approaches in the treatment of diseases characterized by smooth muscle cell hyperplasia such as asthma and chronic bronchitis.

Cytokines induce airway smooth muscle cell hyperresponsiveness to contractile agonists.

The important pathophysiological features of the airways in asthma include exaggerated narrowing to bronchoconstrictor agonists and attenuated relaxation to beta adrenoceptor stimulation. These physiological perturbations are associated with inflammation and remodelling of the airways, the latter including an increase in airway smooth muscle cell mass, disruption of the airway epithelium, and changes in the airway tissue extracellular matrix. Recent evidence suggests that cytokines, important molecules modulating airway inflammation, also directly decrease airway smooth muscle responsiveness to beta adrenergic agents, stimulate cytokine secretion, inhibit or promote airway smooth muscle proliferation, and "prime" airway smooth muscle to become hyperresponsive to bronchoconstrictors. Characterisation of the cellular and biochemical events that are involved in activation of airway smooth muscle is likely to be the major consideration in the design of future therapies for asthma. Because calcium is an essential regulatory element for cell growth and cell contraction, it is likely that alterations in calcium mobilisation may, in part, play a role in creating an airway smooth muscle phenotype that is hyperresponsive to contractile agonists. Further studies will be required to determine the precise mechanisms involved in cytokine modulation of calcium homeostasis in airway smooth muscle.