New IL-17 family members promote Th1 or Th2 responses in the lung: in vivo function of the novel cytokine IL-25

We have biologically characterized two new members of the IL-17 cytokine family: IL-17F and IL-25. In contrast to conventional in vitro screening approaches, we have characterized the activity of these new molecules by direct in vivo analysis and have compared their function to that of other IL-17 family members. Intranasal administration of adenovirus expressing IL-17, IL-17C, or IL-17F resulted in bronchoalveolar lavage neutrophilia and inflammatory gene expression in the lung. In contrast, intranasal administration of IL-25-expressing adenovirus or IL-25 protein resulted in the production of IL-4, IL-5, IL-13, and eotaxin mRNA in the lung and marked eosinophilia in the bronchoalveolar lavage and lung tissue. Mice given intranasal IL-25 also developed epithelial cell hyperplasia, increased mucus secretion, and airway hyperreactivity. IL-25 gene expression was detected following Aspergillus and Nippostrongylus infection in the lung and gut, respectively. IL-25-induced eosinophilia required IL-5 and IL-13, but not IL-4 or T cells. Following IL-25 administration, the IL-5(+) staining cells were CD45R/B220(+), Thy-1(+/-), but were NK1.1-, Ly-6G(GR-1)-, CD4-, CD3-, and c-kit-negative. gamma-common knockout mice did not develop eosinophilia in response to IL-25, nor were IL-5(+) cells detected. These findings suggest the existence of a previously unrecognized cell population that may initiate Th2-like responses by responding to IL-25 in vivo. Further, these data demonstrate the heterogeneity of function within the IL-17 cytokine family and suggest that IL-25 may be an important mediator of allergic disease via production of IL-4, IL-5, IL-13, and eotaxin.     

CD4+CD25+ T cells regulate airway eosinophilic inflammation by modulating the Th2 cell phenotype

We used a TCR-transgenic mouse to investigate whether Th2-mediated airway inflammation is influenced by Ag-specific CD4+CD25+ regulatory T cells. CD4+CD25+ T cells from DO11.10 mice expressed the transgenic TCR and mediated regulatory activity. Unexpectedly, depletion of CD4+CD25+ T cells before Th2 differentiation markedly reduced the expression of IL-4, IL-5, and IL-13 mRNA and protein when compared with unfractionated (total) CD4+ Th2 cells. The CD4+CD25--derived Th2 cells also expressed decreased levels of IL-10 but were clearly Th2 polarized since they did not produce any IFN-gamma. Paradoxically, adoptive transfer of CD4+CD25--derived Th2 cells into BALB/c mice induced an elevated airway eosinophilic inflammation in response to OVA inhalation compared with recipients of total CD4+ Th2 cells. The pronounced eosinophilia was associated with reduced levels of IL-10 and increased amounts of eotaxin in the bronchoalveolar lavage fluid. This Th2 phenotype characterized by reduced Th2 cytokine expression appeared to remain stable in vivo, even after repeated exposure of the animals to OVA aerosols. Our results demonstrate that the immunoregulatory properties of CD4+CD25+ T cells do extend to Th2 responses. Specifically, CD4+CD25+ T cells play a key role in modulating Th2-mediated pulmonary inflammation by suppressing the development of a Th2 phenotype that is highly effective in vivo at promoting airway eosinophilia. Conceivably, this is partly a consequence of regulatory T cells facilitating the production of IL-10.     

Expression of the Th1 chemokine IFN-gamma-inducible protein 10 in the airway alters mucosal allergic sensitization in mice

Although the preliminary characterization of chemokines and their receptors has been prolific, comparatively little is known about the role of chemokines in the evolution of immune responses. We speculate that the preferential recruitment of a particular immune cell population has implications for the short- and long-term features of an adaptive response. To test this hypothesis, we employed adenovirus-mediated gene transfer to express the Th1-affiliated, CXC chemokine IFN-gamma-inducible protein (IP) 10 in the airways of mice undergoing a mucosal sensitization regimen known to result in a Th2-polarized allergic response. This resulted in a approximately 60-75% inhibition of eosinophils in the bronchoalveolar lavage (BAL); these inflammatory changes were accompanied by enhanced IFN-gamma, ablated IL-4, and, peculiarly, unaltered IL-5 and eotaxin levels in the BAL. The effect of IP-10 expression was shown to be dependent on IFN-gamma, as there was no statistically significant reduction in BAL eosinophilia in IFN-gamma knockout mice subjected to the IP-10 intervention. Flow cytometric analysis of mononuclear cells in the lung revealed a approximately 60% reduction in the fraction of CD4(+) cells expressing T1/ST2, a putative Th2 marker, and a parallel increase in the proportion expressing intracellular IFN-gamma following IP-10 treatment. The effect of IP-10 expression at the time of initial Ag encounter is persistent, as mice rechallenged with OVA following the resolution of acute inflammation exhibited reduced eosinophilia and IL-4 in the BAL. Collectively, these data illustrate that local expression of the chemokine IP-10 can introduce Th1 phenomena to a Th2-predisposed context and subvert the development of a Th2 response.     

IL-12-dependent vascular cell adhesion molecule-1 expression contributes to airway eosinophilic inflammation in a mouse model of asthma-like reaction

Bronchial-alveolar eosinophilic inflammation is among the characteristic pathological changes in asthma, which has been shown to be correlated with type 2 cytokine and chemokine production. Exogenous IL-12 has been found to be inhibitory for pulmonary eosinophilia in reported studies. Using a murine asthma-like model induced by OVA, we found in the present study that IL-12 gene knockout (KO) mice showed substantially reduced airway recruitment of eosinophils compared with wild-type control mice following OVA sensitization/challenge, although the levels of circulating eosinophils were comparable in these two groups of mice. Cytokine analysis showed Ag-driven Th1 (IFN-gamma) and Th2 (IL-4, IL-5, IL-10, and IL-13) cytokine production by CD4 T cells from local draining lymph nodes and spleen. Similarly, local eotaxin production was comparable in wild-type and IL-12 KO mice. In contrast, immunohistochemical analysis showed that the expression of VCAM-1 on the lung endothelium of IL-12 KO mice was dramatically less than that in wild-type mice. Furthermore, administration of rIL-12 at the stage of sensitization and challenge with OVA restored airway eosinophilia and VCAM-1 expression in IL-12 KO mice. The results suggest that endogenous IL-12 contributes to the recruitment of eosinophils into airways observed in asthma, possibly via enhancement of the expression of VCAM-1 on local vascular endothelial cells.     

The effect of IL-5 and eotaxin expression in the lung on eosinophil trafficking and degranulation and the induction of bronchial hyperreactivity

The mechanisms regulating the selective migration and degranulation of eosinophils in the asthmatic lung and the subsequent development of airways hyperreactivity (AHR) have not been fully delineated. In this investigation, we have employed a novel transgene model to facilitate the dissection of the contributions of IL-5 and/or eotaxin to eosinophil function in the absence of complex tissue signals derived from the allergic lung. Gene transfer of IL-5 and/or eotaxin to the lungs of naive mice induced a pronounced and selective airways eosinophilia, but did not result in eosinophil degranulation or AHR. Airways eosinophilia occurred independently of the induction of a blood eosinophilia, but was markedly augmented by the coexpression of both cytokines and/or by the transient mobilization of eosinophils from the bone marrow by the administration of i.v. IL-5. However, for eosinophil degranulation and AHR to occur, the inhalation of Ag was required in association with IL-5 and eotaxin expression. Investigations in IL-5-deficient mice linked eosinophilia, and not solely IL-5 and eotaxin, with the induction of AHR. Furthermore, eosinophil degranulation and AHR were dependent on CD4+ T cells. Importantly, this investigation shows that IL-5 regulates eosinophilia within the lung as well as in the circulation and also amplifies eotaxin-induced chemotaxis in the airway compartment. Moreover, the interplay between these cytokines, CD4+ T cells, and factors generated by Ag inhalation provides fundamental signals for eosinophil degranulation and the induction of AHR.     

Vaccine-induced immunity against Helicobacter pylori infection is impaired in IL-18-deficient mice

Protective immunity against Helicobacter pylori infection in mice has been associated with a strong Th1 response, involving IL-12 as well as IFN-gamma, but recent studies have also demonstrated prominent eosinophilic infiltration, possibly linked to local Th2 activity in the gastric mucosa. In this study we investigated the role of IL-18, because this cytokine has been found to be a coregulator of Th1 development as well as involved in Th2-type responses with local eotaxin production that could influence gastric eosinophilia and resistance to infection. We found that IL-18(-/-) mice failed to develop protection after oral immunization with H. pylori lysate and cholera toxin adjuvant, indicating an important role of IL-18 in protection. Well-protected C57BL/6 wild-type (WT) mice demonstrated substantial influx of CD4(+) T cells and eosinophilic cells in the gastric mucosa, whereas IL-18(-/-) mice had less gastritis, few CD4(+) T cells, and significantly reduced numbers of eosinophilic cells. T cells in well-protected WT mice produced increased levels of IFN-gamma and IL-18 to recall Ag. By contrast, unprotected IL-18(-/-) mice exhibited significantly reduced gastric IFN-gamma and specific IgG2a Ab levels. Despite differences in gastric eosinophilic cell infiltration, protected WT and unprotected IL-18(-/-) mice had comparable levels of local eotaxin, suggesting that IL-18 influences protection via Th1 development and IFN-gamma production rather than through promoting local production of eotaxin and eosinophilic cell infiltration.     

Effects of Th2 cytokines on chemokine expression in the lung: IL-13 potently induces eotaxin expression by airway epithelial cells

Airway inflammation associated with asthma is characterized by massive infiltration of eosinophils, mediated in part by specific chemoattractant factors produced in the lung. Allergen-specific Th2 cells appear to play a central role in asthma; for example, adoptively transferred Th2 cells induced lung eosinophilia associated with induction of specific chemokines. Interestingly, Th2 supernatant alone administered intranasally to naive mice induced eotaxin, RANTES, monocyte-chemotactic protein-1, and KC expression along with lung eosinophilia. We tested the major cytokines individually and found that IL-4 and IL-5 induced higher levels of macrophage-inflammatory protein-1alpha and KC; IL-4 also increased the production of monocyte-chemotactic protein-1; IL-13 and IL-4 induced eotaxin. IL-13 was by far the most potent inducer of eotaxin; indeed, a neutralizing anti-IL-13 Ab removed most of the eotaxin-inducing activity from Th2 supernatants, although it did not entirely block the recruitment of eosinophils. While TNF-alpha did not stimulate eotaxin production by itself, it markedly augmented eotaxin induction by IL-13. IL-13 was able to induce eotaxin in the lung of JAK3-deficient mice, suggesting that JAK3 is not required for IL-13 signaling in airway epithelial cells; however, eosinophilia was not induced in this situation, suggesting that JAK3 transduces other IL-13-mediated mechanisms critical for eosinophil recruitment. Our study suggests that IL-13 is an important mediator in the pathogenesis of asthma and therefore a potential target for asthma therapy.     

Interleukin-12 inhibits eotaxin secretion of cultured primary lung cells and alleviates airway inflammation in vivo

The mechanisms that cause the inflammation of airway and lung tissue in asthma have been studied extensively. It is noted that type 1T helper cell (Th1)-related cytokines could decrease the accumulation of eosinophils in lung tissue and relieve airway constriction. But the therapeutic mechanisms of Th1 cytokines remain unclear. In this study, interleukin-12 (IL-12) DNA plasmid as a therapeutic reagent was delivered intravenously. Bronchoalveolar lavage (BAL) fluids were collected from IL-12 treated and control mice, and analyzed for cell composition and eotaxin level. The results showed that IL-12 DNA plasmid could effectively inhibit eosinophilia and airway inflammation in vivo. The level of eotaxin in BAL fluid also decreased. To further investigate the effect of Th1-related cytokines such as IL-12 or interferon-gamma (IFN-gamma) on the eotaxin level produced by lung cells, primary lung cell culture was established. The results demonstrated that both IL-12 and IFN-gamma could suppress eotaxin secretion from IL-13 or IL-4 stimulated primary lung cell culture. Moreover, the inhibitory effect of IL-12 could not be reversed by the administration of anti-IFN-gamma antibody. All the evidences suggested that IL-12 could regulate airway inflammation by suppressing the eotaxin secretion of lung tissue through an IFN-gamma independent mechanism.     

Distinct spatial requirement for eosinophil-induced airways hyperreactivity

T helper (Th)-2-derived cytokines and their involvement in the recruitment and activation of inflammatory cells crucially orchestrate asthma pathogenesis. A notable cellular component of this allergy-induced inflammation is the eosinophil. However, whether the eosinophil is an obligatory mediator for enhancing airways hyperreactivity (AHR) to cholinergic stimuli, a watershed of the asthmatic lung, is somewhat controversial. In this investigation we have endeavoured to define the spatial requirements for IL-4 and IL-13, and the downstream effector molecules, IL-5 and the CC chemokine eotaxin, for the recruitment of eosinophils and the development of AHR in a murine model of allergic pulmonary disease. These studies are of particular importance considering clinical trials, with either the soluble IL-4Ralpha subunit or a humanized anti-IL-5 antibody, are being conducted. Interestingly, our studies show that depletion of both IL-4 and IL-13 is necessary to ablate pulmonary eosinophilia and AHR, and that this may be attributed to the role these cytokines play in regulating the expression of the eosinophil- activating molecules, IL-5 and eotaxin. While it is clear that depletion of IL-5 diminishes pulmonary eosinophilia, we demonstrate in BALB/c mice that a deficiency in both IL-5 and eotaxin is necessary to abolish both the trafficking of eosinophils to the lung and AHR. However, in contrast to the neutrophil-rich inflammation observed in mice deficient in both IL-4 and IL-13, inflammation per se in mice deficient in both IL-5 and eotaxin is significantly attenuated. This suggests that asthma immunotherapy may be better directed towards the eosinophil- activating molecules IL-5 and eotaxin, rather than towards pleiotrophic molecules such IL-4 and IL-13, which are additionally important in modulating alternative inflammatory responses.     

IL-12 contributes to allergen-induced airway inflammation in experimental asthma

Lack of sufficient IL-12 production has been suggested to be one of the basic underlying mechanisms in atopy, but a potential role of IL-12 in established allergic airway disease remains unclear. We took advantage of a mouse model of experimental asthma to study the role of IL-12 during the development of bronchial inflammation. Administration of anti-IL-12p35 or anti-IL-12p40 mAb to previously OVA-sensitized BALB/c mice concomitantly with exposure to nebulized OVA, abolished both the development of bronchial hyperresponsiveness to metacholine as well as the eosinophilia in bronchoalveolar lavage fluid and peripheral blood. Anti-IL-12 treatment reduced CD4(+) T cell numbers and IL-4, IL-5, and IL-13 levels in the bronchoalveolar lavage fluid and the mRNA expression of IL-10, eotaxin, RANTES, MCP-1, and VCAM-1 in the lung. Anti-IL-12p35 treatment failed to show these effects in IFN-gamma knockout mice pointing to the essential role of IFN-gamma in IL-12-induced effects. Neutralization of IL-12 during the sensitization process aggravated the subsequent development of allergic airway inflammation. These data together with recent information on the role of dendritic cells in both the sensitization and effector phase of allergic respiratory diseases demonstrate a dual role of IL-12. Whereas IL-12 counteracts Th2 sensitization, it contributes to full-blown allergic airway disease upon airway allergen exposure in the postsensitization phase, with enhanced recruitment of CD4(+) T cells and eosinophils and with up-regulation of Th2 cytokines, chemokines, and VCAM-1. IFN-gamma-producing cells or cells dependent on IFN-gamma activity, play a major role in this unexpected proinflammatory effect of IL-12 in allergic airway disease.     

IL-5 promotes eosinophil trafficking to the esophagus

Eosinophil infiltration into the esophagus occurs in a wide range of diseases; however, the underlying pathophysiological mechanisms involved are largely unknown. We now report that the Th2 cytokine, IL-5, is necessary and sufficient for the induction of eosinophil trafficking to the esophagus. We show that transgenic mice overexpressing IL-5 under the control of a T cell (CD2) or a small intestinal enterocyte (fatty acid-binding protein) promoter have markedly increased eosinophil numbers in the esophagus. For example, esophageal eosinophil levels are 1.9 +/- 0.9 and 121 +/- 14 eosinophils/mm(2) in wild-type and CD2-IL-5-transgenic mice, respectively. Consistent with this effect being mediated by a systemic mechanism, pharmacological administration of IL-5 via a miniosmotic pump in the peritoneal cavity resulted in blood and esophageal eosinophilia. To examine the role of IL-5 in oral Ag-induced esophageal eosinophilia, eosinophilic esophagitis was induced by allergen exposure in IL-5-deficient and wild-type mice. Importantly, IL-5-deficient mice were resistant to eosinophilic esophagitis. Finally, we examined the role of eotaxin when IL-5 was overproduced in vivo. Esophageal eosinophil levels in CD2-IL-5-transgenic mice were found to decrease 15-fold in the absence of the eotaxin gene; however, esophageal eosinophil numbers in eotaxin-deficient IL-5-transgenic mice still remained higher than wild-type mice. In conclusion, these studies demonstrate a central role for IL-5 in inducing eosinophil trafficking to the esophagus.     

IL-4 differentially regulates eotaxin and MCP-4 in lung epithelium and circulating mononuclear cells

To investigate the mechanisms of eosinophil recruitment in allergic airway inflammation, we examined the effects of interleukin (IL)-4, a Th2-type cytokine, on eotaxin and monocyte chemoattractant protein-4 (MCP-4) expression in human peripheral blood mononuclear cells (PBMCs; n = 10), in human lower airway mononuclear cells (n = 5), in the human lung epithelial cell lines A549 and BEAS-2B, and in human cultured airway epithelial cells. IL-4 inhibited eotaxin and MCP-4 mRNA expression induced by IL-1 beta and tumor necrosis factor-alpha in PBMCs but did not significantly inhibit expression in epithelial cells. Eotaxin and MCP-4 mRNA expression was not significantly induced by proinflammatory cytokines in lower airway mononuclear cells. IL-1 beta-induced eotaxin and MCP-4 protein production was also inhibited by IL-4 in PBMCs, whereas IL-4 enhanced eotaxin protein production in A549 cells. In contrast, dexamethasone inhibited eotaxin and MCP-4 expression in both PBMCs and epithelial cells. The divergent effects of IL-4 on eotaxin and MCP-4 expression between PBMCs and epithelial cells may create chemokine concentration gradients between the subepithelial layer and the capillary spaces that may promote the recruitment of eosinophils to the airway in Th2-type responses.     

CD8+ T cell-mediated airway hyperresponsiveness and inflammation is dependent on CD4+IL-4+ T cells

CD4+ T cells, particularly Th2 cells, play a pivotal role in allergic airway inflammation. However, the requirements for interactions between CD4+ and CD8+ T cells in airway allergic inflammation have not been delineated. Sensitized and challenged OT-1 mice in which CD8+ T cells expressing the transgene for the OVA(257-264) peptide (SIINFEKL) failed to develop airway hyperresponsiveness (AHR), airway eosinophilia, Th2 cytokine elevation, or goblet cell metaplasia. OT-1 mice that received naive CD4+IL-4+ T cells but not CD4+IL-4- T cells before sensitization developed all of these responses to the same degree as wild-type mice. Moreover, recipients of CD4+IL-4+ T cells developed significant increases in the number of CD8+IL-13+ T cells in the lung, whereas sensitized OT-1 mice that received primed CD4+ T cells just before challenge failed to develop these responses. Sensitized CD8-deficient mice that received CD8+ T cells from OT-1 mice that received naive CD4+ T cells before sensitization increased AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged with allergen. In contrast, sensitized CD8-deficient mice receiving CD8+ T cells from OT-1 mice without CD4+ T cells developed reduced AHR and eosinophil numbers in bronchoalveolar lavage fluid when challenged. These data suggest that interactions between CD4+ and CD8+ T cells, in part through IL-4 during the sensitization phase, are essential to the development of CD8+IL-13+ T cell-dependent AHR and airway allergic inflammation.     

Eosinophils and T lymphocytes possess distinct roles in bleomycin-induced lung injury and fibrosis

Leukocyte infiltration is characteristic of lung injury and fibrosis, and its role during tissue repair and fibrosis is incompletely understood. We found that overexpression of IL-5 in transgenic mice (IL-5(TG)) or by adenoviral gene transfer increased bleomycin (blm)-induced lung injury, fibrosis, and eosinophilia. Surprisingly, blm-treated IL-5-deficient (IL-5(-/-)) mice also developed pronounced pulmonary fibrosis but characterized by marked T lymphocyte infiltration and absence of eosinophilia. In both murine strains however, induction of lung TGF-beta expression was evident. Purified lung eosinophils from blm-treated IL-5(TG) mice stimulated alpha-smooth muscle actin and collagen expression in mouse lung fibroblasts, without affecting proliferation. Furthermore instillation of purified eosinophils into murine lungs resulted in extension of blm-induced lung fibrosis, thus confirming a role for eosinophils. However, lung T lymphocytes from blm-treated IL-5(-/-) mice were able to stimulate fibroblast proliferation but not alpha-smooth muscle actin or collagen expression. Blocking T cell influx by anti-CD3 Abs abrogated lung fibrosis, thus also implicating T lymphocytes as a key participant in fibrosis. Pulmonary fibrosis in IL-5(TG) mice was preferentially associated with type 2 cytokines (IL-4 and IL-13), whereas fibrotic lesions in IL-5(-/-) animals were accompanied by proinflammatory cytokine (TNF-alpha, IL-1beta, and IFN-gamma) expression. We suggest that eosinophils and T cells contribute distinctly to the development of blm-induced lung fibrosis potentially via their production of different cytokine components, which ultimately induce TGF-beta expression that is intimately involved with the fibrosis.     

OX40 ligation on activated T cells enhances the control of Cryptococcus neoformans and reduces pulmonary eosinophilia

Pulmonary eosinophilia induced in C57BL/6 mice after Cryptococcus neoformans infection is driven by CD4(+) Th2 cells. The immunological mechanisms that protect against eosinophilia are not fully understood. Interaction of OX40 (CD134) and its ligand, OX40L, has been implicated in T cell activation and cell migration. Unlike CD28, OX40 is only expressed on T cells 1-2 days after Ag activation. Manipulation of this pathway would therefore target recently activated T cells, leaving the naive repertoire unaffected. In this study, we show that engagement of OX40 by an OX40L:Ig fusion protein drives IFN-gamma production by CD4(+) T cells and reduces eosinophilia and C. neoformans burden in the lung. Using gene-depleted mice, we show that reduction of eosinophilia and pathogen burden requires IL-12 and/or IFN-gamma. C. neoformans infection itself only partially induces OX40L expression by APCs. Provision of exogenous OX40L reveals a critical role of this pathway in the prevention of C. neoformans-induced eosinophilia.     

豚鼠气道炎症中Eotaxin基因表达的意义

通过气管内滴注葡聚糖诱导豚鼠气道炎症,研究嗜酸细胞在气道炎症中的意义。用葡聚糖G200(5mg/kg)滴注形成气道炎症,进行支气管肺泡灌洗,通过RTPCR方法,检测气道炎症时肺匀浆Eotaxin基因的表达。结果可见,葡聚糖G200所致豚鼠肺损伤后Eotaxin的mRNA表达水平随葡聚糖G200刺激时间延长而明显升高(P<0.05),同时支气管肺泡灌洗液中白细胞数及上清液中Th2型细胞因子IL4也随之升高(P<0.05);试验中采用甲强龙琥珀酸钠抑制气道炎症,与盐水对照组比较P>0.05。可见,用葡聚糖G200进行气管滴注是形成气管炎症简单而实用的动物模型;Eotaxin在聚集、活化炎性细胞过程中起重要作用;糖皮质激素类药物能有效抑制Eotaxin的表达。     

Influenza A virus infection inhibits the efficient recruitment of Th2 cells into the airways and the development of airway eosinophilia

Most infections with respiratory viruses induce Th1 responses characterized by the generation of Th1 and CD8(+) T cells secreting IFN-gamma, which in turn have been shown to inhibit the development of Th2 cells. Therefore, it could be expected that respiratory viral infections mediate protection against asthma. However, the opposite seems to be true, because viral infections are often associated with the exacerbation of asthma. For this reason, we investigated what effect an influenza A (flu) virus infection has on the development of asthma. We found that flu infection 1, 3, 6, or 9 wk before allergen airway challenge resulted in a strong suppression of allergen-induced airway eosinophilia. This effect was associated with strongly reduced numbers of Th2 cells in the airways and was not observed in IFN-gamma- or IL-12 p35-deficient mice. Mice infected with flu virus and immunized with OVA showed decreased IL-5 and increased IFN-gamma, eotaxin/CC chemokine ligand (CCL)11, RANTES/CCL5, and monocyte chemoattractant protein-1/CCL2 levels in the bronchoalveolar lavage fluid, and increased airway hyperreactivity compared with OVA-immunized mice. These results suggest that the flu virus infection reduced airway eosinophilia by inducing Th1 responses, which lead to the inefficient recruitment of Th2 cells into the airways. However, OVA-specific IgE and IgG1 serum levels, blood eosinophilia, and goblet cell metaplasia in the lung were not reduced by the flu infection. Flu virus infection also directly induced AHR and goblet cell metaplasia. Taken together, our results show that flu virus infections can induce, exacerbate, and suppress features of asthmatic disease in mice.     

The pulmonary environment promotes Th2 cell responses after nasal-pulmonary immunization with antigen alone, but Th1 responses are induced during instances of intense immune stimulation

The purpose of this study was to determine the nature of the CD4(+) Th cell responses induced after nasal-pulmonary immunization, especially those coinciding with previously described pulmonary inflammation associated with the use of the mucosal adjuvant, cholera toxin (CT). The major T cell population in the lungs of naive mice was CD4(+), and these cells were shown to be predominantly of Th2 type as in vitro polyclonal stimulation resulted in IL-4, but not IFN-gamma, production. After nasal immunization with influenza Ag alone, Th2 cytokine mRNA (IL-4 and IL-5) levels were increased, whereas there was no change in Th1 cytokine (IL-2 and IFN-gamma) mRNA expression. The use of the mucosal adjuvant, CT, markedly enhanced pulmonary Th2-type responses; however, there was also a Th1 component to the T cell response. Using in vitro Ag stimulation of pulmonary lymphocytes, influenza virus-specific cytokine production correlated with the mRNA cytokine results. Furthermore, there was a large increase in CD4(+) Th cell numbers in lungs after nasal immunization using CT, correlating with the pulmonary inflammatory infiltrate previously described. Coincidentally, both macrophage-inflammatory protein-1alpha (MIP-1alpha) and MIP-1beta mRNA expression increased in the lungs after immunization with Ag plus CT, while only MIP-1beta expression increased when mice were given influenza Ag alone. Our study suggests a mechanism to foster Th1 cell recruitment into the lung, which may impact on pulmonary immune responses. Thus, while Th2 cell responses may be prevalent in modulating mucosal immunity in the lungs, Th1 cell responses contribute to pulmonary defenses during instances of intense immune stimulation.     

IL-13 is required for eosinophil entry into the lung during respiratory syncytial virus vaccine-enhanced disease

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in children. Children previously vaccinated with a formalin-inactivated RSV vaccine experienced enhanced morbidity and mortality upon natural RSV infection. Histological analysis revealed the presence of eosinophils in the pulmonary infiltrate of the vaccinated children. Eosinophils are characteristic of Th2 responses, and Th2 cells are known to be necessary to induce pulmonary eosinophilia in RSV-infected BALB/c mice previously immunized with a recombinant vaccinia virus (vv) expressing the RSV G protein (vvG). Using IL-13-deficient mice, we find that IL-13 is necessary for eosinophils to reach the lung parenchyma and airways of vvG-immunized mice undergoing RSV challenge infection. IL-13 acts specifically on eosinophils as the magnitude of pulmonary inflammation, RSV G protein-specific CD4 T cell responses, and virus clearance were not altered in IL-13-deficient mice. After RSV challenge, eosinophils were readily detectable in the blood and bone marrow of vvG-immunized IL-13-deficient mice, suggesting that IL-13 is required for eosinophils to transit from the blood into the lung. Pulmonary levels of CCL11 and CCL22 protein were significantly reduced in IL-13-deficient mice indicating that IL-13 mediates the recruitment of eosinophils into the lungs by inducing the production of chemokines important in Th2 cell and eosinophil chemotaxis.