Asthma is characterized by airway inflammation, remodeling, and hyperresponsiveness to contractile stimuli that promote airway constriction and wheezing. Here we present evidence that sphingosine 1-phosphate (SPP) is a potentially important inflammatory mediator implicated in the pathogenesis of airway inflammation and asthma. SPP levels were elevated in the airways of asthmatic (but not control) subjects following segmental antigen challenge, and this increase was correlated with a concomitant increase in airway inflammation. Because human airway smooth muscle (ASM) cells expressed EDG receptors for SPP , we examined whether SPP may play a role in airway inflammation and remodeling, by affecting ASM cell growth, contraction, and cytokine secretion. SPP is mitogenic and augments EGF-and thrombininduced DNA proliferation by increasing G 1 /S progression. SPP increased phosphoinositide turnover and intracellular calcium mobilization, the acute signaling events that affect ASM contraction. By modulating adenylate cyclase activity and cAMP accumulation, SPP had potent effects on cytokine secretion. Although SPP inhibited TNF-α-induced RANTES release, it induced substantial IL-6 secretion alone and augmented production of IL-6 induced by TNF-α. These studies are the first to associate SPP with airway inflammation and to identify SPP as an effective regulator of ASM growth, contraction and synthetic functions.Key words: cAMP • EDG receptors • cytokines • mitogenesis • cytosolic calcium sthma, a common chronic disease, is characterized by airway hyper-responsiveness and reversible airflow obstruction. Exposure to environmental antigen, a frequent trigger of acute asthmatic attacks, induces an inflammatory reaction in the airway characterized in part by an influx of lymphocytes and eosinophils that secrete various agents capable of A perpetuating inflammation and provoking airway smooth muscle (ASM) contraction. Accordingly, the majority of therapeutic agents in asthma seek to minimize the development or consequences of airway inflammation or directly promote ASM relaxation.Recently, a more chronic feature of asthma, termed "airway remodeling", has drawn the attention of asthma research. Airway remodeling refers to structural alterations in the bronchial wall characterized by ASM hypertrophy and hyperplasia, epithelial denudation, mucus gland hyperplasia, lamina recticularis thickening, and vasculogenesis. The functional consequence of these histological findings is to render the airway irreversibly obstructed in some susceptible asthmatics. Others (1-4) and we (5) have recently suggested a prominent role for ASM in orchestrating both the acute inflammatory reaction and the chronic features of airway remodeling that occur in asthma. This assertion is supported by observations that ASM mass is increased in the bronchi of severe chronic asthmatics (6), that numerous agents that are elevated in the asthmatic airway are mitogenic to ASM in vitro (5), and that ASM expresses adhesion molecules (7) and secretes numerous cytokin...

Approximately 5% to 10% of patients with asthma have severe disease that is refractory or poorly responsive to inhaled corticosteroid therapy. These patients represent an important unmet clinical need because they experience considerable morbidity and mortality and consume a disproportionately large amount of health care resources. TNF-α is a proinflammatory cytokine that has been implicated in many aspects of the airway pathology in asthma. Evidence is emerging to suggest that it might play an important role in severe refractory disease. The development of novel TNF-α antagonists has allowed us to test the role of this cytokine in vivo. Preliminary studies have demonstrated an improvement in asthma quality of life, lung function, and airway hyperresponsiveness and a reduction in exacerbation frequency in patients treated with anti-TNF-α therapy. However, there is marked heterogeneity in response, suggesting that benefit is likely to be reserved to a small subgroup. Importantly, where efficacy is reported, this also needs to be considered in the context of concerns about the safety of anti-TNF-α therapies. Therefore the challenge for clinicians is to evaluate the risk/benefit ratio of these therapies in individual patients with asthma. KeywordsAsthma; refractory asthma; TNF-α; mast cells; airway smooth muscle Asthma is a common disease that is increasing in prevalence worldwide. 1 Its prevalence is highest in industrialized countries, where it affects about 15% of the adult population. 2 The mainstay of therapy is inhaled corticosteroids, and the majority of asthma symptoms are controlled with inhaled corticosteroids alone or in combination with long-acting β-agonists. 3 However, 5% to 10% of the asthmatic population have severe refractory disease. [4][5][6] This group is important because they are responsible for a disproportionate share of the health Evidence supports a role for anti-TNF-α as a potential new therapy in severe refractory asthma. 7,8 Initial enthusiasm fueled by these early studies has been dampened by concerns over safety, 9 and its efficacy is likely to be confined to a small subgroup of patients with severe asthma. There is an increasing recognition that there is considerable phenotypic heterogeneity in severe refractory asthma, 10,11 and it is therefore perhaps predictable that the efficacy of novel specific therapies will be limited to subphenotypes.In this review we acknowledge the importance of heterogeneity in asthma, summarize the biology of TNF-α with particular reference to its role in asthma and the development of airway hyperresponsiveness (AHR), and review the findings of currently published clinical trials of anti-TNF-α therapy in asthma. TNF-α BIOLOGY AND SIGNALINGTNF-α is the most widely studied pleiotropic cytokine of the TNF superfamily. TNF-α is an important cytokine in the innate immune response, which plays a key role in the immediate host defense against invading microorganisms before activation of the adaptive immune system. 12 It is principally produced by macrop...

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.