Social stress enhances allergen-induced airway inflammation in mice and inhibits corticosteroid responsiveness of cytokine production

Beta adrenergic blockade decreases the immunomodulatory effects of social disruption stress

During physiological or psychological stress, catecholamines produced by the sympathetic nervous system (SNS) regulate the immune system. Previous studies report that the activation of β-adrenergic receptors (βARs) mediates the actions of catecholamines and increases pro-inflammatory cytokine production in a number of different cell types. The impact of the SNS on the immune modulation of social defeat has not been examined. The following studies were designed to determine whether SNS activation during social disruption stress (SDR) influences anxiety-like behavior as well as the activation, priming, and glucocorticoid resistance of splenocytes after social stress. CD-1 mice were exposed to one, three, or six cycles of SDR and HPLC analysis of the plasma and spleen revealed an increase in catecholamines. After six cycles of SDR the open field test was used to measure behaviors characteristic of anxiety and indicated that the social defeat induced increase in anxiety-like behavior was blocked by pre-treatment with the β-adrenergic antagonist propranolol. Pre-treatment with the β-adrenergic antagonist propranolol did not significantly alter corticosterone levels indicating no difference in activation of the hypothalamic-pituitary-adrenal axis. In addition to anxiety-like behavior the SDR induced splenomegaly and increase in plasma IL-6, TNFα, and MCP-1 were each reversed by pre-treatment with propranolol. Furthermore, flow cytometric analysis of cells from propranolol pretreated mice reduced the SDR-induced increase in the percentage of CD11b(+) splenic macrophages and significantly decreased the expression of TLR2, TLR4, and CD86 on the surface of these cells. In addition, supernatants from 18h LPS-stimulated ex vivo cultures of splenocytes from propranolol-treated SDR mice contained less IL-6. Likewise propranolol pre-treatment abrogated the glucocorticoid insensitivity of CD11b(+) cells ex vivo when compared to splenocytes from SDR vehicle-treated mice. Together, this study demonstrates that the immune activation and priming effects of SDR result, in part, as a consequence of SNS activation.

Peripheral innate immune challenge exaggerated microglia activation, increased the number of inflammatory CNS macrophages, and prolonged social withdrawal in socially defeated mice

Repeated social defeat (RSD) activates neuroendocrine pathways that have a significant influence on immunity and behavior. Previous studies from our lab indicate that RSD enhances the inflammatory capacity of CD11b⁺ cells in the brain and promotes anxiety-like behavior in an interleukin (IL)-1 and β-adrenergic receptor-dependent manner. The purpose of this study was to determine the degree to which mice subjected to RSD were more responsive to a secondary immune challenge. Therefore, RSD or control (HCC) mice were injected with saline or lipopolysaccharide (LPS) and activation of brain CD11b⁺ cells and behavioral responses were determined. Peripheral LPS (0.5 mg/kg) injection caused an extended sickness response with exaggerated weight loss and prolonged social withdrawal in socially defeated mice. LPS injection also amplified mRNA expression of IL-1β, tumor necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), and CD14 in enriched CD11b⁺ cells isolated from socially defeated mice. In addition, IL-1β mRNA levels in enriched CD11b⁺ cells remained elevated in socially defeated mice 24 h and 72 h after LPS. Moreover, microglia and CNS macrophages isolated from socially defeated mice had the highest CD14 expression after LPS injection. Both social defeat and LPS injection increased the percentage of CD11b⁺/CD45(high) macrophages in the brain and the number of inflammatory macrophages (CD11b⁺/CD45(high)/CCR2⁺) was highest in RSD-LPS mice. Anxiety-like behavior was increased by social defeat, but was not exacerbated by the LPS challenge. Nonetheless, reduced locomotor activity and increased social withdrawal were still present in socially defeated mice 72 h after LPS. Last, LPS-induced microglia activation was most evident in the hippocampus of socially defeated mice. Taken together, these findings demonstrate that repeated social defeat enhanced the neuroinflammatory response and caused prolonged sickness following innate immune challenge.

Trichostatin A abrogates airway constriction, but not inflammation, in murine and human asthma models

Histone deacetylase (HDAC) inhibitors may offer novel approaches in the treatment of asthma. We postulate that trichostatin A (TSA), a Class 1 and 2 inhibitor of HDAC, inhibits airway hyperresponsiveness in antigen-challenged mice. Mice were sensitized and challenged with Aspergillus fumigatus antigen (AF) and treated with TSA, dexamethasone, or vehicle. Lung resistance (R(L)) and dynamic compliance were measured, and bronchial alveolar lavage fluid (BALF) was analyzed for numbers of leukocytes and concentrations of cytokines. Human precision-cut lung slices (PCLS) were treated with TSA and their agonist-induced bronchoconstriction was measured, and TSA-treated human airway smooth muscle (ASM) cells were evaluated for the agonist-induced activation of Rho and intracellular release of Ca(2+). The activity of HDAC in murine lungs was enhanced by antigen and abrogated by TSA. TSA also inhibited methacholine (Mch)-induced increases in R(L) and decreases in dynamic compliance in naive control mice and in AF-sensitized and -challenged mice. Total cell counts, concentrations of IL-4, and numbers of eosinophils in BALF were unchanged in mice treated with TSA or vehicle, whereas dexamethasone inhibited the numbers of eosinophils in BALF and concentrations of IL-4. TSA inhibited the carbachol-induced contraction of PCLS. Treatment with TSA inhibited the intracellular release of Ca(2+) in ASM cells in response to histamine, without affecting the activation of Rho. The inhibition of HDAC abrogates airway hyperresponsiveness to Mch in both naive and antigen-challenged mice. TSA inhibits the agonist-induced contraction of PCLS and mobilization of Ca(2+) in ASM cells. Thus, HDAC inhibitors demonstrate a mechanism of action distinct from that of anti-inflammatory agents such as steroids, and represent a promising therapeutic agent for airway disease.

The intestinal microbiota are necessary for stressor-induced enhancement of splenic macrophage microbicidal activity

The indigenous microbiota impact mucosal, as well as systemic, immune responses, but whether the microbiota are involved in stressor-induced immunomodulation has not been thoroughly tested. A well characterized murine stressor, called social disruption (SDR), was used to study whether the microbiota are involved in stressor-induced enhancement of macrophage reactivity. Exposure to the SDR Stressor enhanced the ability of splenic macrophages to produce microbicidal mediators (e.g., inducible nitric oxide synthase (iNOS), superoxide anion, and peroxynitrite) and to kill target Escherichia coli. Exposure to the SDR Stressor also increased cytokine production by LPS-stimulated splenic macrophages. These effects, however, were impacted by the microbiota. Microbicidal activity and cytokine mRNA in splenic macrophages from Swiss Webster germfree mice that lack any commensal microbiota were not enhanced by exposure to the SDR Stressor. However, when germfree mice were conventionalized by colonizing them with microbiota from CD1 conventional donor mice, exposure to the SDR Stressor again increased microbicidal activity and cytokine mRNA. In follow-up experiments, immunocompetent conventional CD1 mice were treated with a cocktail of antibiotics to disrupt the intestinal microbiota. While exposure to the SDR Stressor-enhanced splenic macrophage microbicidal activity and cytokine production in vehicle-treated mice, treatment with antibiotics attenuated the SDR Stressor-induced increases in splenic macrophage reactivity. Treatment with antibiotics also prevented the stressor-induced increase in circulating levels of bacterial peptidoglycan, suggesting that translocation of microbiota-derived peptidoglycan into the body primes the innate immune system for enhanced activity. This study demonstrates that the microbiota play a crucial role in stressor-induced immunoenhancement.

Peripheral blood gene expression changes during allergen inhalation challenge in atopic asthmatic individuals

OBJECTIVES

(1) To investigate the effects of globin mRNA depletion in detecting differential gene expression in peripheral blood and (2) to investigate changes in peripheral blood gene expression in atopic asthmatic individuals undergoing allergen inhalation challenge.

METHODS

Asthmatic subjects (20-60 years of age, with stable, mild allergic asthma, n = 9) underwent allergen inhalation challenges. All had an early asthmatic response of ≥20% fall in forced expiratory volume in 1 second. Blood was collected immediately prior to and 2 hours after allergen challenge using PAXgene tubes (n = 4) and EDTA tubes (n = 5). Aliquots of the PAXgene blood samples were subjected to globin reduction (PAX-GR). Transcriptome analysis was performed using Affymetrix GeneChip(®) Human Gene 1.0 ST arrays. Data were preprocessed using factor analysis for robust microarray summarization and analyzed using linear models for microarrays. Pathway analyses were performed using Ingenuity Pathway Analysis.

RESULTS

Globin reduction uncovered probe sets of lower abundance. However, it significantly reduced the ability to detect differentially expressed genes (DEGs) when compared to non-globin-reduced PAXgene samples (PAX-NGR). Combined transcriptional analysis of four PAX-NGR and five EDTA sample pairs identified 1595 DEGs associated with allergen inhalation challenge (false discovery rate ≤ 5%), with the top-ranked network of perturbed biological functions consisting of inflammatory response, cellular movement, and immune cell trafficking.

CONCLUSIONS

While we have demonstrated a diminished ability to detect DEGs after globin reduction, we have nevertheless identified significant changes in the peripheral blood transcriptome of people with mild asthma 2 hours after allergen inhalation challenge.

Parental stress increases the detrimental effect of traffic exposure on children's lung function

RATIONALE

Emerging evidence indicates that psychosocial stress enhances the effect of traffic exposure on the development of asthma.

OBJECTIVES

We hypothesized that psychosocial stress would also modify the effect of traffic exposure on lung function deficits.

METHODS

We studied 1,399 participants in the Southern California Children's Health Study undergoing lung function testing (mean age, 11.2 yr). We used hierarchical mixed models to assess the joint effect of traffic-related air pollution and stress on lung function.

MEASUREMENTS AND MAIN RESULTS

Psychosocial stress in each child's household was assessed based on parental response to the perceived stress scale (range, 0-16) at study entry. Exposures to nitric oxide, nitrogen dioxide, and total oxides of nitrogen (NOx), surrogates of the traffic-related pollution mixture, were estimated at schools and residences based on a land-use regression model. Among children from high-stress households (parental perceived stress scale > 4) deficits in FEV1 of 4.5 (95% confidence interval, -6.5 to -2.4) and of 2.8% (-5.7 to 0.3) were associated with each 21.8 ppb increase in NOx at homes and schools, respectively. These pollutant effects were significantly larger in the high-stress compared with lower-stress households (interaction P value 0.007 and 0.05 for residential and school NOx, respectively). No significant NOx effects were observed in children from low-stress households. A similar pattern of association was observed for FVC. The observed associations for FEV1 and FVC remained after adjusting for sociodemographic factors and after restricting the analysis to children who do not have asthma.

CONCLUSIONS

A high-stress home environment is associated with increased susceptibility to lung function effects of air pollution both at home and at school.

Social disruption induced priming of CNS inflammatory response to Theiler's virus is dependent upon stress induced IL-6 release

Chronic social disruption stress (SDR) exacerbates acute and chronic phase Theiler's murine encephalomyelitis virus (TMEV) infection, a mouse model of multiple sclerosis. However, the precise mechanism by which this occurs remains unknown. The present study suggests that SDR exacerbates TMEV disease course by priming virus-induced neuroinflammation. It was demonstrated that IL-1β mRNA expression increases following acute SDR; however, IL-6 mRNA expression, but not IL-1β, is upregulated in response to chronic SDR. Furthermore, this study demonstrated SDR prior to infection increases infection related central IL-6 and IL-1β mRNA expression, and administration of IL-6 neutralizing antibody during SDR reverses this increase in neuroinflammation.

Pathophysiology of allergic inflammation

Allergic inflammation is due to a complex interplay between several inflammatory cells, including mast cells, basophils, lymphocytes, dendritic cells, eosinophils, and sometimes neutrophils. These cells produce multiple inflammatory mediators, including lipids, purines, cytokines, chemokines, and reactive oxygen species. Allergic inflammation affects target cells, such as epithelial cells, fibroblasts, vascular cells, and airway smooth muscle cells, which become an important source of inflammatory mediators. Sensory nerves are sensitized and activated during allergic inflammation and produce symptoms. Allergic inflammatory responses are orchestrated by several transcription factors, particularly NF-κB and GATA3. Inflammatory genes are also regulated by epigenetic mechanisms, including DNA methylation and histone modifications. There are several endogenous anti-inflammatory mechanisms, including anti-inflammatory lipids and cytokines, which may be defective in allergic disease, thus amplifying and perpetuating the inflammation. Better understanding of the pathophysiology of allergic inflammation has identified new therapeutic targets but developing effective novel therapies has been challenging. Corticosteroids are highly effective with a broad spectrum of anti-inflammatory effects, including epigenetic modulation of the inflammatory response and suppression of GATA3.

Social defeat promotes specific cytokine variations within the prefrontal cortex upon subsequent aggressive or endotoxin challenges

Stressful experiences typically have short-lived neuroendocrine and neurochemical effects, but the processes leading to these biological alterations may be sensitized so that later challenges promote exaggerated responses. As stressors and immunogenic insults have both been associated with inflammatory immune variations within the brain, we assessed whether a social defeat stressor would result in augmented corticosterone release and mRNA expression of pro-inflammatory cytokines within the prefrontal cortex (PFC) upon later social defeat (sensitization) or endotoxin (lipopolysaccharide: LPS) challenges (cross-sensitization). In the absence of a prior stressor experience, the social defeat challenge did not affect prefrontal interleukin (IL)-1β or tumor necrosis factor (TNF)-α mRNA expression, but increased that of IL-6, whereas LPS increased the expression of each cytokine. Among mice that had initially been repeatedly defeated, IL-1β and TNF-α expression was enhanced after the social defeat challenge, whereas this was not evident in response to the LPS challenge. In contrast, the initial social defeat stressor had protracted effects in that increase of IL-6 expression was limited upon subsequent challenge with either social defeat or LPS. Previous social stressor experiences also limited the corticosterone rise ordinarily elicited by either social defeat or LPS treatment. It seems that a powerful stressor, such as social defeat, may have persistent effects on later corticosterone and cytokine responses to different types of stressful insults (social versus systemic challenges), but the nature of the effects varies with the specific process assessed.

Corticotropin-releasing hormone receptor-1 and 2 activity produces divergent resistance against stress-induced pulmonary Streptococcus pneumoniae infection

Utilizing a murine model of S. pneumoniae infection and restraint stress, we determined how corticotropin releasing hormone (CRH-R) receptors impacts disease. CRH-R1 (antalarmin) and CRH-R2 (astressin2B) antagonists were administered intraperitoneally prior to restraint stress followed by pulmonary S. pneumoniae infection. CRH-R1 inhibition is not protective against pneumococcal disease induced by stress. Conversely, CRH-R2 inhibition attenuates stress-induced bacterial growth and significantly prevented severe sepsis. Neutrophillic responses were associated with CRH receptor-specific disease outcome providing a potential cellular target for stress-induced susceptibility to the development of severe pneumococcal disease. CRH receptor-mediated effects on immune responses could prove valuable for novel therapeutics.

The neuropeptide calcitonin gene-related peptide affects allergic airway inflammation by modulating dendritic cell function

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) is released in the lung by sensory nerves during allergic airway responses. Pulmonary dendritic cells (DC) orchestrating the allergic inflammation could be affected by CGRP.

OBJECTIVE

To determine the immunomodulatory effects of CGRP on DC function and its impact on the induction of allergic airway inflammation.

METHODS

CGRP receptor expression on lung DC was determined by RT-PCR and immunofluorescence staining. The functional consequences of CGRP receptor triggering were evaluated in vitro using bone marrow-derived DC. DC maturation and the induction of ovalbumin (OVA)-specific T cell responses were analysed by flow cytometry. The in vivo relevance of the observed DC modulation was assessed in a DC-transfer model of experimental asthma. Mice were sensitized by an intrapharyngeal transfer of OVA-pulsed DC and challenged with OVA aerosol. The impact of CGRP pretreatment of DC on airway inflammation was characterized by analysing differential cell counts and cytokines in bronchoalveolar lavage fluid (BALF), lung histology and cytokine responses in mediastinal lymph nodes.

RESULTS

RT-PCR, immunofluorescence and cAMP assay demonstrated the expression of functionally active CGRP receptors in lung DC. RT-PCR revealed a transcriptional CGRP receptor down-regulation during airway inflammation. CGRP specifically inhibited the maturation of in vitro generated DC. Maturation was restored by blocking with the specific antagonist CGRP(8-37) . Consequently, CGRP-pretreated DC reduced the activation and proliferation of antigen-specific T cells and induced increased the numbers of T regulatory cells. The transfer of CGRP-pretreated DC diminished allergic airway inflammation in vivo, shown by reduced eosinophil numbers and increased levels of IL-10 in BALF.

CONCLUSIONS AND CLINICAL RELEVANCE

CGRP inhibits DC maturation and allergen-specific T cell responses, which affects the outcome of the allergic airway inflammation in vivo. This suggests an additional mechanism by which nerve-derived mediators interfere with local immune responses. Thus, CGRP as an anti-inflammatory mediator could represent a new therapeutic tool in asthma therapy.

Expression analysis of asthma candidate genes during human and murine lung development

BACKGROUND

Little is known about the role of most asthma susceptibility genes during human lung development. Genetic determinants for normal lung development are not only important early in life, but also for later lung function.

OBJECTIVE

To investigate the role of expression patterns of well-defined asthma susceptibility genes during human and murine lung development. We hypothesized that genes influencing normal airways development would be over-represented by genes associated with asthma.

METHODS

Asthma genes were first identified via comprehensive search of the current literature. Next, we analyzed their expression patterns in the developing human lung during the pseudoglandular (gestational age, 7-16 weeks) and canalicular (17-26 weeks) stages of development, and in the complete developing lung time series of 3 mouse strains: A/J, SW, C57BL6.

RESULTS

In total, 96 genes with association to asthma in at least two human populations were identified in the literature. Overall, there was no significant over-representation of the asthma genes among genes differentially expressed during lung development, although trends were seen in the human (Odds ratio, OR 1.22, confidence interval, CI 0.90-1.62) and C57BL6 mouse (OR 1.41, CI 0.92-2.11) data. However, differential expression of some asthma genes was consistent in both developing human and murine lung, e.g. NOD1, EDN1, CCL5, RORA and HLA-G. Among the asthma genes identified in genome wide association studies, ROBO1, RORA, HLA-DQB1, IL2RB and PDE10A were differentially expressed during human lung development.

CONCLUSIONS

Our data provide insight about the role of asthma susceptibility genes during lung development and suggest common mechanisms underlying lung morphogenesis and pathogenesis of respiratory diseases.

Modeling social influences on human health

Social interactions have long-term physiological, psychological, and behavioral consequences. Social isolation is a well-recognized but little understood risk factor and prognostic marker of disease; it can have profoundly detrimental effects on both mental and physical well-being, particularly during states of compromised health. In contrast, the health benefits associated with social support (both reduced risk and improved recovery) are evident in a variety of illnesses and injury states; however, the mechanisms by which social interactions influence disease pathogenesis remain largely unidentified. The substantial health impact of the psychosocial environment can occur independently of traditional disease risk factors and is not accounted for solely by peer-encouraged development of health behaviors. Instead, social interactions are capable of altering shared pathophysiological mechanisms of multiple disease states in distinct measurable ways. Converging evidence from animal models of injury and disease recapitulates the physiological benefits of affiliative social interactions and establishes several endogenous mechanisms (inflammatory signals, glucocorticoids, and oxytocin) by which social interactions influence health outcomes. Taken together, both clinical and animal research are undoubtedly necessary to develop a complete mechanistic understanding of social influences on health.

Influence of physical exercise on neuroimmunological functioning and health: aging and stress

Chronic and acute stress, with associated pathophysiology, are implicated in a variety of disease states, with neuroimmunological dysregulation and inflammation as major hazards to health and functional sufficiency. Psychosocial stress and negative affect are linked to elevations in several inflammatory biomarkers. Immunosenescence, the deterioration of immune competence observed in the aged aspect of the life span, linked to a dramatic rise in morbidity and susceptibility to diseases with fatal outcomes, alters neuroimmunological function and is particularly marked in the neurodegenerative disorders, e.g., Parkinson's disease and diabetes. Physical exercise diminishes inflammation and elevates agents and factors involved in immunomodulatory function. Both the alleviatory effects of life-long physical activity upon multiple cancer forms and the palliative effects of physical activity for individuals afflicted by cancer offer advantages in health intervention. Chronic conditions of stress and affective dysregulation are associated with neuroimmunological insufficiency and inflammation, contributing to health risk and mortality. Physical exercise regimes have induced manifest anti-inflammatory benefits, mediated possibly by brain-derived neurotrophic factor. The epidemic proportions of metabolic disorders, obesity, and diabetes demand attention; several variants of exercise regimes have been found repeatedly to induce both prevention and improvement under both laboratory and clinical conditions. Physical exercise offers a unique non-pharmacologic intervention incorporating multiple activity regimes, e.g., endurance versus resistance exercise that may be adapted to conform to the particular demands of diagnosis, intervention and prognosis inherent to the staging of autoimmune disorders and related conditions.

Epinephrine-primed murine bone marrow-derived dendritic cells facilitate production of IL-17A and IL-4 but not IFN-γ by CD4+ T cells

Sympathetic activation leading to the release of epinephrine and norepinephrine, is known as an important regulatory circuit related to immune-mediated diseases. However, questions still remain on the behavior of antigen presenting cells (APC) dictated by stress-induced sympathetic neurotransmitters. The purpose of this study was to examine the fate of bone marrow-derived dendritic cell (BMDC)-associated influences on resting CD4(+) T cell activation. We hypothesize that pre-exposure of dendritic cells (DCs) can modify the intensity of cytokine production, leading to preference in resting CD4(+) T cell activation. BMDCs were pre-treated with epinephrine for 2h followed by subsequent treatment of lipopolysaccharide (LPS). Subsequently, BMDCs were cocultured with purified CD4(+) T cells from mouse spleen in the absence or presence of anti-CD3 stimulation in epinephrine-free media. Epinephrine pre-treatment enhanced surface expression of MHCII, CD80 and CD86. Quantitative RT-PCR showed that epinephrine pre-treatment induced a significant transcriptional decrease of IL-12p40 and a significant increase of IL-12p35 and IL-23p19. In addition, β2-adrenergic-blockade was shown to reverse these effects. Epinephrine pre-treatment also induced a significant decrease of IL-12p70 and a significant increase of IL-23 and IL-10 cytokine production. Importantly, these changes corresponded with increased IL-4 and IL-17A, but not IFN-g cytokine production by CD4(+) T cells in a b2-adrenergic receptor-dependent manner. These results suggest that exposure to stress-derived epinephrine dictates dendritic cells to generate a dominant Th2/Th17 phenotype in the context of subsequent exposure to a pathogenic stimulus.

Social disruption induces lung inflammation

Social disruption (SDR) is a well-characterized mouse stressor that causes changes in immune cell reactivity in response to inflammatory stimuli. In this study, we found that SDR in the absence of an immune challenge induced pulmonary inflammation and increased pulmonary myeloperoxidase activity. The percentage of neutrophils within the lungs increased 2-fold after social disruption. Monocyte accumulation in the lungs was also significantly increased. In addition, SDR increased the percentage of neutrophils that expressed CD11b, indicating that more neutrophils were in an activated state. In the lungs, we observed an increased level of the inflammatory cytokine, IL-1beta, as well as higher levels of KC/CXCL1, MIP-2/CXCL2, and MCP-1/CCL2, which are chemokines responsible for neutrophil and monocyte recruitment. Furthermore, social disruption led to increased lung expression of the adhesion molecules P-selectin, E-selectin, and ICAM-1, which localize and recruit immune cells. These data support previous findings of an inflammatory environment induced by SDR. We demonstrate that this effect also occurs in the pulmonary milieu and in the absence of an inflammatory stimulus.

Social stress and asthma: the role of corticosteroid insensitivity

Psychosocial stress alters susceptibility to infectious and systemic illnesses and may enhance airway inflammation in asthma by modulating immune cell function through neural and hormonal pathways. Stress activates the hypothalamic-pituitary-adrenal axis. Release of endogenous glucocorticoids, as a consequence, may play a prominent role in altering the airway immune homeostasis. Despite substantial corticosteroid and catecholamine plasma levels, chronic psychosocial stress evokes asthma exacerbations. Animal studies suggest that social stress induces corticosteroid insensitivity that in part may be a result of impaired glucocorticoid receptor expression and/or function. Such mechanisms likely promote and amplify airway inflammation in response to infections, allergen, or irritant exposure. This review discusses evidence of an altered corticosteroid responsive state as a consequence of chronic psychosocial stress. Elucidation of the mechanisms of stress-induced impairment of glucocorticoid responsiveness and immune homeostasis may identify novel therapeutic targets that could improve asthma management.

Airway cytokine responses to acute and repeated stress in a murine model of allergic asthma

Although stress is known to exacerbate asthma, the underlying mechanisms are unclear. Using a murine model of allergic asthma, Th1 (interleukin [IL]-2 and gamma-interferon [IFN-γ]) and Th2 (IL-4 and IL-5) airway cytokine responses and Th1:Th2 cytokine ratios to acute and repeated stress were examined in bronchoalveolar lavage fluid (BALF). Asthmatic mice showed significantly higher IL-4 level and Th2 predominance, compared with healthy mice. To acute stress, asthmatic mice significantly increased IL-4 but decreased IFN-γ levels favoring Th2 predominance, whereas healthy mice significantly decreased IL-4 level favoring Th1 predominance in BALF. To repeated stress, asthmatic mice significantly decreased IFN-γ, IL-4 and IL-5 levels overall favoring Th1 predominance, whereas healthy mice basically maintained the same response profile shown to acute stress. These findings suggest that a significant shift toward Th2 predominance in asthmatic mice under acute stress may be a mechanism underlying exacerbation of asthma.