Cigarette smoke extract induces thymic stromal lymphopoietin expression, leading to T(H)2-type immune responses and airway inflammation

Lactobacillus bulgaricus OLL1181 activates the aryl hydrocarbon receptor pathway and inhibits colitis

Increasing evidence suggests that the aryl hydrocarbon receptor (AhR) pathway has an important role in the regulation of inflammatory responses. Most recently, we have shown that the activation of the AhR pathway by a potent AhR agonist inhibits the development of dextran sodium sulfate (DSS)-induced colitis, a model of human ulcerative colitis, by the induction of prostaglandin E2 (PGE2) in the large intestine. Because several strains of probiotic lactic acid bacteria have been reported to inhibit DSS-induced colitis by unidentified mechanisms, we hypothesized that particular strains of lactic acid bacterium might have the potential to activate the AhR pathway, thereby inhibiting DSS-induced colitis. This study investigated whether there are specific lactic acid bacterial strains that can activate the AhR pathway, and if so, whether this AhR-activating potential is associated with suppression of DSS-induced colitis. By using AhR signaling reporter cells, we found that Lactobacillus bulgaricus OLL1181 had the potential to activate the AhR pathway. OLL1181 also induced the mRNA expression of cytochrome P450 family 1A1 (CYP1A1), a target gene of the AhR pathway, in human colon cells, which was inhibited by the addition of an AhR antagonist, α-naphthoflavon (αNF). In addition, mice treated orally with OLL1181 showed an increase in CYP1A1 mRNA expression in the large intestine and amelioration of DSS-induced colitis. Thus, OLL1181 can induce activation of the intestinal AhR pathway and inhibit DSS-induced colitis in mice. This strain of lactic acid bacterium has therefore the potential to activate the AhR pathway, which may be able to suppress colitis.

Role of thymic stromal lymphopoietin (TSLP) in palifermin-mediated immune modulation and protection from acute murine graft-versus-host disease

Using the C57BL/6→(C57BL/6 x DBA/2)F(1)-hybrid model of acute graft-versus-host disease (GVHD), we previously showed that treating the donor mice with palifermin provides protection from morbidity and a shift from Th1 to Th2 cytokine production. To determine whether thymic stromal lymphopoietin (TSLP) is involved in palifermin-mediated immune modulation, we used donors from the following groups: (1) untreated wild-type donors, (2) palifermin-treated wild-type donors, (3) untreated TSLPR(-/-) donors, and (4) palifermin-treated TSLPR(-/-) donors. Survival in the recipients was 0%, 100%, 31%, and 0%, for groups 1-4, respectively, indicating that TSLP responsiveness is required for palifermin-mediated protection from GVHD. We also found that the increases in Th2 cytokine levels that are induced by palifermin treatment are obviated in TSLPR(-/-) donors, and that protection from GVHD (group 2) is associated with a higher percentage of CD4(+)CD25(+)Foxp3(+) cells in the graft. Collectively, our findings show that when palifermin and TSLP act in concert, the predominant effect is protection in this model.

Epithelial cells from smokers modify dendritic cell responses in the context of influenza infection

Epidemiologic evidence suggests that cigarette smoking is a risk factor for infection with influenza, but the mechanisms underlying this susceptibility remain unknown. To ascertain if airway epithelial cells from smokers demonstrate a decreased ability to orchestrate an influenza-induced immune response, we established a model using differentiated nasal epithelial cells (NECs) from nonsmokers and smokers, co-cultured with peripheral blood monocyte-derived dendritic cells (mono-DCs) from nonsmokers. NEC/mono-DC co-cultures were infected with influenza A virus and analyzed for influenza-induced immune responses 24 hours after infection. We observed that NECs from smokers, as well as mono-DCs co-cultured with NECs from smokers, exhibited suppressed influenza-induced, interferon-related proteins interferon regulatory factor-7, Toll-like receptor-3, and retinoic acid inducible gene-1, likely because of the suppressed production of IFNα from the NECs of smokers. Furthermore, NEC/mono-DC co-cultures using NECs from smokers exhibited suppressed concentrations of T-cell/natural killer cell chemokine interferon gamma-induced protein 10 (IP-10) after infection with influenza, indicating that NECs from smokers may skew early influenza-induced Th1 responses. In contrast, NEC/mono-DC co-cultures using NEC from smokers contained increased influenza-induced concentrations of the Th2 chemokine thymic stromal lymphopoeitin (TSLP). In addition, NECs from smokers cultured alone had increased influenza-induced concentrations of the Th2 chemokine thymus and activation-regulated chemokine (TARC). Using this model, we demonstrated that in the context of infection with influenza, NECs obtained from smokers create an overall cytokine microenvironment that suppresses the interferon-mediated Th1 response and enhances the TSLP-TARC-mediated Th2 response, with the potential to modify the responses of DCs. Smoking-induced alterations in the Th1/Th2 balance may play a role in developing underlying susceptibilities to respiratory viral infections, and may also promote the likelihood of acquiring Th2 proallergic diseases.

Thymic stromal lymphopoietin in cigarette smoke-exposed human airway smooth muscle

Thymic stromal lymphopoietin (TSLP) is a newly identified IL-7-like cytokine known to be expressed in airway biopsies of patients with asthma and chronic obstructive pulmonary disease. As both diseases may be induced or exacerbated by cigarette smoking, it is possible that TSLP represents an important link between cigarette smoke exposure and inflammatory signaling in the airways. In this regard, TSLP appears to also be expressed in airway smooth muscle (ASM); however, its role is unknown. In the current study, we examined TSLP and the TSLP receptor (TSLP-R) expression and function in human ASM cells under normal conditions and following exposure to cigarette smoke extract (CSE). Western blot analysis of human ASM cells showed significant expression of TSLP and TSLP-R, with increased expression of both by overnight exposure to 1 or 2% CSE. Furthermore, CSE increased TSLP release by ASM. In parallel experiments using enzymatically dissociated human ASM cells loaded with the Ca(2+) indicator fura 2-AM and imaged using fluorescence microscopy, we evaluated the effects of CSE exposure on intracellular Ca(2+) ([Ca(2+)](i)) responses to agonist stimulation. [Ca(2+)](i) responses to histamine were increased with overnight CSE exposure. Exposure to TSLP also resulted in elevated responses, which were blunted by TSLP and TSLP-R Abs. Importantly, the enhancing effects of CSE on [Ca(2+)](i) responses were also blunted by these Abs. These effects were associated with CSE- and TSLP-induced changes in STAT5 phosphorylation. Overall, these novel data suggest that cigarette smoke, TSLP, and ASM are functionally linked and that cigarette smoke-induced increase in airway contractility may be mediated via ASM-derived increases in TSLP signaling.

The T helper type 2 response to cysteine proteases requires dendritic cell-basophil cooperation via ROS-mediated signaling

The mechanisms that initiate T helper type 2 (T(H)2) responses are poorly understood. Here we demonstrate that cysteine protease-induced T(H)2 responses occur via 'cooperation' between migratory dermal dendritic cells (DCs) and basophils positive for interleukin 4 (IL-4). Subcutaneous immunization with papain plus antigen induced reactive oxygen species (ROS) in lymph node DCs and in dermal DCs and epithelial cells of the skin. ROS orchestrated T(H)2 responses by inducing oxidized lipids that triggered the induction of thymic stromal lymphopoietin (TSLP) by epithelial cells mediated by Toll-like receptor 4 (TLR4) and the adaptor protein TRIF; by suppressing production of the T(H)1-inducing molecules IL-12 and CD70 in lymph node DCs; and by inducing the DC-derived chemokine CCL7, which mediated recruitment of IL-4(+) basophils to the lymph node. Thus, the T(H)2 response to cysteine proteases requires DC-basophil cooperation via ROS-mediated signaling.

Activation of the aryl hydrocarbon receptor pathway may ameliorate dextran sodium sulfate-induced colitis in mice

The aryl hydrocarbon receptor (AhR) recognizes numerous small xenobiotic and natural molecules, such as dioxin and natural chemicals, and is involved in the metabolism of these compounds. AhR also has a regulatory role in inflammatory responses. This study investigated whether the activation of the AhR pathway affects dextran sodium sulfate (DSS)-induced colitis, an ulcerative colitis-like model, in mice. DSS-induced colitis was ameliorated by pretreatment with a potent AhR activator, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in mice. In addition, the mice pretreated with TCDD showed increased prostaglandin E2 (PGE2) production in the colon, and inhibition of PGE2 production by indomethacin abrogated the inhibitory effects of TCDD on DSS-induced colitis. Collectively, the activation of the AhR pathway by TCDD may ameliorate DSS-induced colitis, at least in part, through PGE2 production.

The influence of TSLP on the allergic response

Exposure to allergens first occurs at body surfaces in direct contact with the environment such as the skin, airways, and gastrointestinal tract, and compelling evidence suggests that allergic inflammatory responses are profoundly influenced by the products of epithelial cells located at these sites. One such product is thymic stromal lymphopoietin (TSLP), which is capable of affecting multiple cell lineages involved in allergic reactions. In this review we discuss recent work that has provided insight into the role TSLP plays in both aberrant and protective allergic inflammatory responses, as well as regulation, associations with disease, sources, and functions of this important cytokine.

The role of thymic stromal lymphopoietin in allergic inflammation and chronic obstructive pulmonary disease

Thymic stromal lymphopoietin (TSLP) primes dendritic cells to promote a Th2 inflammatory response. Its action is mediated by a heterodimeric receptor which consists of the interleukin-7 receptor alpha chain and the TSLP receptor chain (TSLPR). TSLPR resembles the common gamma chain subunit utilized by many type 1 cytokine receptors. Normal epithelial cells, keratinocytes, and stromal cells constitutively express TSLP. Dendritic cells that are activated by TSLP promote the development of CD4(+) T cells into pro-inflammatory Th2 cells. TSLP thus plays a potentially important role in the pathogenesis of allergic inflammation in asthma and atopic dermatitis. TSLP also has direct effects on other types of cells in the bronchial mucosa. It is over-expressed in the bronchial mucosa in chronic obstructive pulmonary disease (COPD), which is traditionally described as a Th1-related disease, as well as severe asthma, which is traditionally described as a Th2-related disease. In this review we will discuss TSLP expression, function, and available and potential mechanisms in both allergic inflammation and COPD.

Mouse models to unravel the role of inhaled pollutants on allergic sensitization and airway inflammation

Air pollutant exposure has been linked to a rise in wheezing illnesses. Clinical data highlight that exposure to mainstream tobacco smoke (MS) and environmental tobacco smoke (ETS) as well as exposure to diesel exhaust particles (DEP) could promote allergic sensitization or aggravate symptoms of asthma, suggesting a role for these inhaled pollutants in the pathogenesis of asthma. Mouse models are a valuable tool to study the potential effects of these pollutants in the pathogenesis of asthma, with the opportunity to investigate their impact during processes leading to sensitization, acute inflammation and chronic disease. Mice allow us to perform mechanistic studies and to evaluate the importance of specific cell types in asthma pathogenesis. In this review, the major clinical effects of tobacco smoke and diesel exhaust exposure regarding to asthma development and progression are described. Clinical data are compared with findings from murine models of asthma and inhalable pollutant exposure. Moreover, the potential mechanisms by which both pollutants could aggravate asthma are discussed.

Concomitant inhalation of cigarette smoke and aerosolized protein activates airway dendritic cells and induces allergic airway inflammation in a TLR-independent way

Cigarette smoking is associated with the development of allergic asthma. In mice, exposure to cigarette smoke sensitizes the airways toward coinhaled OVA, leading to OVA-specific allergic inflammation. Pulmonary dendritic cells (DCs) are professional APCs involved in immunosurveillance and implicated in the induction of allergic responses in lung. We investigated the effects of smoking on some of the key features of pulmonary DC biology, including trafficking dynamics and cellular activation status in different lung compartments. We found that cigarette smoke inhalation greatly amplified DC-mediated transport of inhaled Ags to mediastinal lymph nodes, a finding supported by the up-regulation of CCR7 on airway DCs. Pulmonary plasmacytoid DCs, which have been involved in inhalational tolerance, were reduced in number after smoke exposure. In addition, combined exposure to cigarette smoke and OVA aerosol increased surface expression of MHC class II, CD86, and PDL2 on airway DCs, while ICOSL was strongly down-regulated. Although inhaled endotoxins, which are also present in cigarette smoke, have been shown to act as DC activators and Th2-skewing sensitizers, TLR4-deficient and MyD88 knockout mice did not show impaired eosinophilic airway inflammation after concomitant exposure to cigarette smoke and OVA. From these data, we conclude that cigarette smoke activates the pulmonary DC network in a pattern that favors allergic airway sensitization toward coinhaled inert protein. The TLR independency of this phenomenon suggests that alternative immunological adjuvants are present in cigarette smoke.

A subcytotoxic dose of subtilase cytotoxin prevents lipopolysaccharide-induced inflammatory responses, depending on its capacity to induce the unfolded protein response

Subtilase cytotoxin (SubAB) is the prototype of a newly identified family of AB(5) cytotoxins produced by Shiga toxigenic Escherichia coli. SubAB specifically cleaves the essential endoplasmic reticulum (ER) chaperone BiP (GRP78), resulting in the activation of ER stress-induced unfolded protein response (UPR). We have recently shown that the UPR following ER stress can suppress cellular responses to inflammatory stimuli during the later phase, in association with inhibition of NF-kappaB activation. These findings prompted us to hypothesize that SubAB, as a selective UPR inducer, might have beneficial effects on inflammation-associated pathology via a UPR-dependent inhibition of NF-kappaB activation. The pretreatment of a mouse macrophage cell line, RAW264.7, with a subcytotoxic dose of SubAB-triggered UPR and inhibited LPS-induced MCP-1 and TNF-alpha production associated with inhibition of NF-kappaB activation. SubA(A272)B, a SubAB active site mutant that cannot induce UPR, did not show such effects. In addition, pretreatment with a sublethal dose of SubAB, but not SubA(A272)B, protected the mice from LPS-induced endotoxic lethality associated with reduced serum MCP-1 and TNF-alpha levels and also prevented the development of experimental arthritis induced by LPS in mice. Collectively, although SubAB has been identified originally as a toxin associated with the pathogenesis of hemolytic uremic syndrome, the unique ability of SubAB to selectively induce the UPR may have the potential to prevent LPS-associated inflammatory pathology under subcytotoxic conditions.

Between a cough and a wheeze: dendritic cells at the nexus of tobacco smoke-induced allergic airway sensitization

Exposure to cigarette smoke represents a major risk factor for the development of asthma. Enhanced sensitization toward allergens has been observed in humans and laboratory animals exposed to cigarette smoke. Pulmonary dendritic cells (DCs) are crucially involved in sensitization toward allergens and play an important role in the development of T helper (Th)2-mediated allergic airway inflammation. We propose the concept that aberrant DC activation forms the basis for the deviation of the lung's default tolerogenic response toward allergic inflammation when harmless antigens are concomittantly inhaled with tobacco smoke. This review will summarize evidence suggesting that tobacco smoke can achieve this effect by providing numerous triggers of innate immunity, which can profoundly modulate airway DC biology. Tobacco smoke can affect the airway DC network either directly or indirectly by causing the release of DC-targeted mediators from the pulmonary tissue environment, resulting in the induction of a Th2-oriented pathological immune response. A thorough knowledge of the molecular pathways involved may open the door to novel approaches in the treatment of asthma.