Blockade of CCR4 in a humanized model of asthma reveals a critical role for DC-derived CCL17 and CCL22 in attracting Th2 cells and inducing airway inflammation

BACKGROUND

As Th2 type lymphocytes orchestrate the cardinal features of allergic asthma, inhibiting their recruitment to the lungs could be of therapeutic benefit. Although human Th2 cells express the CCR4 chemokine receptor and increased production of CCR4 ligands has been found in asthmatic airways, studies in animals have reached contradictory conclusions on whether blocking this pathway would be beneficial.

OBJECTIVE

As a lack of efficacy might be due to differences between mouse and man, we readdressed this question using a humanized severe combined immunodeficiency model of asthma.

METHODS

Mice received peripheral blood mononuclear cells from house dust mite (HDM) allergic asthmatic patients and then underwent bronchial challenge with HDM.

RESULTS

This resulted in marked allergic inflammation and bronchial hyper-reactivity. Administration of CCR4 blocking antibody abolished the airway eosinophilia, goblet cell hyperplasia, IgE synthesis and bronchial hyper-reactivity. In this chimeric system, human CD11c+ dendritic cells (DCs) were the predominant source of CCR4 ligands, suggesting that DC-derived chemokines attract Th2 cells. In separate experiments using human DCs, in vitro exposure to HDM of DCs from HDM allergic patients but not healthy controls caused CCL17 and CCL22 release that resulted in chemoattraction of polarized human Th2 cells in a CCR4-dependent way.

CONCLUSIONS

Taken together, our data provide proof of concept that CCR4 blockade inhibits the salient features of asthma and justify further clinical development of CCR4 antagonists for this disease.

Immunoreactivity profile of peripheral blood mononuclear cells from patients with ragweed-induced allergic rhinitis

BACKGROUND

Seasonal rhinitis is manifested by a series of nasal symptoms in response to exposure to seasonal allergens including ragweed pollen. Understanding its immunological mechanisms may help to better manage the disease.

OBJECTIVE

We sought to determine comprehensively ragweed-induced cytokine and chemokine production by peripheral blood mononuclear cells from normal individuals and patients with seasonal rhinitis sensitized to ragweed pollen, and to assess its regulation by exogenous IL-10.

METHODS

Cells were cultured in the presence or absence of a purified ragweed pollen extract with or without exogenous IL-10. Cytokines and chemokines were measured in the supernatant. Gene expression was evaluated using real-time quantitative reverse transcription PCR.

RESULTS

Ragweed stimulation significantly increased the production of the Th2-associated cytokines IL-5, IL-9 and IL-13, the chemokines CCL17 and CCL22 and the regulatory cytokine IL-10 in allergic patients, whereas transforming growth factor-beta (TGF-beta) production was increased only in normal individuals. No difference was detected between groups in the production of the Th1 cytokine IFN-gamma or the Th1-affiliated chemokines CXCL10 and CXCL11. Exogenous IL-10 significantly suppressed spontaneous and induced production of both Th1- and Th2-associated cytokines and chemokines.

CONCLUSION

Our work demonstrated that locally manifested allergic rhinitis is underlined by a systemic Th2 immune response specific to allergens. The molecular pathogenesis of allergic rhinitis may be linked to a compromised allergen-specific immune regulation, e.g., reduced spontaneous and allergen-induced TGF-beta production in patients compared with healthy controls. Our data also show that IL-10 inhibits both the effector and directional mechanisms of allergen-specific immune response, further supporting its potential therapeutic benefit in preventing and treating allergic diseases.

Fc dependent mechanisms are necessary for ADCC and effective depletion of murine B cells by humanized anti-CD19 mAb. (131.27)

B cell depletion is an effective treatment for autoimmune diseases and B cell malignancies. Successful B cell depletion may be limited by the surface expression of the target antigen. CD19 represents an attractive molecular target that is expressed on the surface of early B cell progenitors through the latter stages of B cell differentiation. In this study we developed a fully humanized CD19 monoclonal antibody mAb 19-1 and two variants with either reduced (19-2) or enhanced (19-3) Fc-FcR binding and evaluated their potential to deplete B cells. In vitro antibody-dependent cellular-mediated cytotoxicity (ADCC) activity of 19-3>19-1>19-2 on human peripheral blood B cells as well as B cell lines (Raji, Daudi, and Ramos) by LDH release or Granzyme B assays. We evaluated in vivo depletion in human CD19 transgenic mice using 19-1, 19-2, and 19-3. 19-1 at 50 ug/mouse i.v. depleted most B cells in blood, spleen, and bone marrow after 7 days following treatment. 19-2 showed little depletion of B cells at a high dose, whereas 19-3 efficiently eliminated B cells in the spleen and blood at low dose. These data demonstrate that transgenic mice expressing human antigens provide an excellent model for testing humanized antibodies in depletion studies, and that Fc-FcR interactions represent the most important mechanism. Targeting B cells with anti-CD19 mAb may be a more effective strategy than existing B cell depletion protocols.

The lung cytokine microenvironment influences molecular events in the lymph nodes during Th1 and Th2 respiratory mucosal sensitization to antigen in vivo

Originally defined by their patterns of cytokine production, Th1 and Th2 cells have been described more recently to express other genes differentially as well, at least in vitro. In this study we compared the expression of Th1- and Th2-associated genes directly during in vivo sensitization to ovalbumin (OVA) in Th1- and Th2-polarized models of airways inflammation. Th1-polarized airway inflammation was achieved by the intranasal instillation of adenoviral vectors (Ad) encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-12, followed by daily aerosolizations of OVA; instillation of Ad/GM-CSF alone with OVA aerosolization led to Th2-polarized responses. Lymph nodes were obtained at various time-points, RNA extracted, and analysed by real-time quantitative polymerase chain reaction (PCR). Consistent with reports from in vitro and human studies, mice undergoing Th1-polarized inflammation showed preferential expression of the transcription factor t-bet, the chemokines IFN-gamma inducible protein (IP)-10 and macrophage inflammatory protein 1 alpha (MIP-1-alpha), and the chemokine receptor CCR5. In contrast, the transcription factor GATA-3, the chemokines I-309 and thymus and activation regulated chemokine (TARC), and the chemokine receptors CCR3 and CCR4 were preferentially expressed in the Th2 model. Importantly, we also show that Ad/transgene expression remains compartmentalized to the lung after intranasal instillation. Flow cytometric analysis of lung myeloid dendritic cells indicated that B7.1 was expressed more strongly in the Th1 model than in the Th2 model. These studies provide a direct comparison of gene expression in in vivo Th1- and Th2-polarized models, and demonstrate that molecular events in the lymph nodes can be altered fundamentally by cytokine expression at distant mucosal sites.

Inhalation of a harmless antigen (ovalbumin) elicits immune activation but divergent immunoglobulin and cytokine activities in mice

BACKGROUND

Exposure to aerosolized harmless antigen such as ovalbumin (OVA) has previously been shown to induce inhalation tolerance, a state characterized by inhibition of IgE synthesis and airway inflammation, upon secondary immunogenic antigen encounter. Immune events associated with this phenomenon are still poorly understood.

OBJECTIVE

The aim of this study was to investigate cellular and molecular mechanisms underlying this state of 'unresponsiveness'.

METHODS

After initial repeated OVA exposure, mice were subjected to a protocol of antigen-induced airway inflammation, encompassing two intraperitoneal injections of OVA adsorbed to aluminium hydroxide followed by airway challenge. We assessed immune events in the draining lymph nodes after sensitization, and in the lungs after challenge.

RESULTS

In animals initially exposed to OVA, we observed, at the time of sensitization, considerable expansion of T cells, many of which expressed the activation markers CD69 and CD25, as well as increased numbers of antigen-presenting cells, particularly B cells. While these animals produced low levels of IgE, the observed elevated levels of IgG1 signified isotype switching. Splenocytes and lymph node cells from OVA-exposed mice produced low levels of IL-4, IL-5, IL-13 and IFN-gamma, indicating aborted effector function of both T helper (Th)2- and Th1-associated cytokines. Real time quantitative polymerase chain reaction (PCR) (TaqMan) analysis of costimulatory molecules in the lungs after in vivo challenge showed that B7.1, B7.2, CD28 and CTLA-4 mRNA expression was low in animals initially exposed to OVA. Ultimately, these events were associated with abrogated airway inflammation and attenuated airway hyper-responsiveness. The decreased inflammation was antigen-specific and independent of IL-10 or IFN-gamma.

CONCLUSION

Initial exposure to OVA establishes a programme that prevents the generation of intact, fully functional inflammatory responses upon secondary antigen encounter. The absence of inflammation, however, is not associated with categorical immune unresponsiveness.

Temporal-spatial analysis of the immune response in a murine model of ovalbumin-induced airways inflammation

The objective of this study was to define phenotypic changes of antigen-presenting cells (APCs) and T cells in a murine model of antigen-induced airways inflammation that involves intraperitoneal sensitization with ovalbumin (OVA)/adjuvant followed by antigen aerosolization. We investigated the APC and T-cell compartments both after sensitization (primary immune response) and after challenge (secondary immune response) at the thoracic lymph nodes (initiation site) and the lung (effector site). Our findings document a major cellular expansion in the lymph nodes after both sensitization and challenge. After sensitization, this expansion was comprised mainly of B cells, a considerable proportion of which expressed B7.2. At this time, T cells were markedly expanded and activated as assessed by CD69 expression; further, although GATA-3 and signal transducer and activator of transcription-6 were expressed at this time point, expression of interleukin (IL)-4, IL-5, and IL-13 messenger RNA (mRNA) levels were marginal. However, in vitro stimulation of lymph-node cells with OVA led to cytokine production. In contrast, 24 h after challenge, but not after sensitization, there was a major expansion of dendritic cells and macrophages in the lungs. This expansion was associated with enhanced expression of both B7.1 and B7.2. We also observed expansion of activated CD3(+)/CD4(+) T cells expressing the T helper-2-associated marker T1/ST2 in the lung, most notably 5 d after challenge. Further, IL-4, IL-5, and IL-13, but not interferon-gamma mRNA were expressed at high levels 3 h after challenge. This study helps to elucidate the "geography" of immune responses generated in a conventional murine model of allergic airways inflammation.

Generation of experimental allergic airways inflammation in the absence of draining lymph nodes

The objective of this study was to investigate the contribution of secondary lymphoid organs in the generation and maintenance of experimental allergic airway inflammation. We employed a previously reported murine model of respiratory mucosal allergic sensitization, induced by repeated aerosolizations of ovalbumin in the context of a GM-CSF airway environment. We executed this protocol in wild-type (WT) and lymphotoxin-alpha-deficient mice (LTalpha-KO) mice, which are devoid of lymph nodes (LNs) and possess rudimentary spleen structures. Despite the lack of pulmonary LNs draining the airway compartment, LTalpha-KO mice were fully capable of mounting a robust inflammatory response in the airways, consisting of Th2 polarized CD4+ T cells and eosinophils. This was accompanied by IL-5, IL-13, and IFN-gamma production by splenocytes and generation of ovalbumin-specific serum IgE. Exposure to the same antigen 7 weeks after complete resolution of airway inflammation once again induced a Th2 polarized infiltrate, demonstrating intact immunological memory. To investigate inherent plasticity in establishing antigen-specific immunity, mice were splenectomized before sensitization. Allergic sensitization was completely abrogated in splenectomized LTalpha-KO mice, compared with eusplenic LTalpha-KO controls. These data demonstrate that secondary lymphoid organs, either LN or spleen, are essential for the generation of allergic airway responses.

The costimulatory molecule ICOS plays an important role in the immunopathogenesis of EAE

The inducible costimulatory molecule (ICOS) is expressed on activated T cells and participates in a variety of important immunoregulatory functions. After the induction of experimental allergic encephalomyelitis in SJL mice with proteolipid protein (PLP), brain ICOS mRNA and protein were up-regulated on infiltrating CD3+ T cells before disease onset. ICOS blockade during the efferent immune response (9-20 days after immunization) abrogated disease, but blockade during antigen priming (1-10 days after immunization) exacerbated disease. Upon culture with PLP and compared with immunized controls, splenocytes produced either decreased interferon-gamma (IFN-gamma, in efferent blockade) or excessive IFN-gamma (in priming blockade). PLP-specific immunoglobulin G1 was decreased in animals treated with anti-ICOS during antigen priming, but not in other groups.

Importance of ICOS-B7RP-1 costimulation in acute and chronic allograft rejection

Primary T cell activation requires B7-CD28 and CD40-CD154 costimulation, but effector T cell functions are considered to be largely independent of these costimulatory pathways. Although blockade of costimulation with cytolytic T lymphocyte-associated antigen 4-immunoglobulin (CTLA-4-Ig) or monoclonal antibody (mAb) to CD154 prolongs allograft survival, chronic rejection follows, which suggests that additional key costimulatory pathways are active in vivo. We found that both antibody to inducible costimulator (anti-ICOS) and an ICOS-Ig fusion protein suppressed intragraft T cell activation and cytokine expression and prolonged allograft survival in a manner similar to that in ICOS-/- allograft recipients. The combination of anti-ICOS therapy and cyclosporin A led to permanent engraftment. In addition, ICOS-B7RP-1 costimulation was required for the development of chronic rejection after CD40-CD154 blockade. These data demonstrate a key role for the ICOS-B7RP-1 pathway in acute and chronic rejection and highlight the benefits of targeting this pathway in combination with the use of conventional immunosuppressive agent.

ICOS is critical for T helper cell-mediated lung mucosal inflammatory responses

We examined the requirement for and cooperation between CD28 and inducible costimulator (ICOS) in effective T helper (TH) cell responses in vivo. We found that both CD28 and ICOS were critical in determining the outcome of an immune response; cytolytic T lymphocyte-associated antigen 4-immunoglobulin (CTLA-4-Ig), ICOS-Ig and/or a neutralizing ICOS monoclonal antibody attenuated T cell expansion, TH2 cytokine production and eosinophilic inflammation. CD28-dependent signaling was essential during priming, whereas ICOS-B7RP-1 regulated TH effector responses, and the up-regulation of chemokine receptors that determine T cell migration. Our data suggests a scenario whereby both molecules regulate the outcome of the immune response but play separate key roles: CD28 primes T cells and ICOS regulates effector responses.

IL-5 deficiency abolishes aspects of airway remodelling in a murine model of lung inflammation

BACKGROUND AND OBJECTIVES

Lung remodelling is a recognized feature of chronic asthma. In the present study, we have used IL-5-deficient mice to evaluate the role of this cytokine and eosinophilic inflammation in the initial stages of the structural changes occurring in the lung after antigen challenge.

METHODS

Ovalbumin-sensitized wild type and IL-5-deficient mice were daily challenged for 5 consecutive days and killed 3 or 7 days after the last challenge to study the inflammatory and remodelling events, respectively.

RESULTS

Wild type mice challenged with ovalbumin exhibited an accumulation of eosinophils in the bronchoalveolar lavage (BAL) fluid, associated with a production of BAL cellular fibronectin. Histological analysis also revealed an antigen-specific increase in epithelial and alveolar cell proliferation together with an increase in mucus producing epithelial cells. Eosinophilic infiltration and the associated lung remodelling were totally abrogated in IL-5-deficient mice. In wild type mice, treated intranasally with 1 microg of murine IL-5 for 5 consecutive days, no BAL eosinophilia and structural changes of the lungs could be observed.

CONCLUSION

Our results demonstrate that eosinophil accumulation, but not IL-5 alone, plays a central role in the initial stages of the lung remodelling process and suggests that therapies directed at inhibiting eosinophilic inflammation may be beneficial in treating chronic asthma.

Regulation and function of T1/ST2 expression on CD4+ T cells: induction of type 2 cytokine production by T1/ST2 cross-linking

The orphan receptor T1/ST2, a member of the IL-1R family, is preferentially expressed on the surface of murine Th2 cells. In this study, we analyzed the kinetics and function of T1/ST2 expression on Th2 cells in vitro. Whereas naive CD4(+) cells did not express T1/ST2, most CD4(+) cells became T1/ST2(+) upon repeated antigenic stimulation under Th2-polarizing conditions. Flow cytometric analyses revealed that the kinetics of T1/ST2 expression on Th2 cells was delayed compared with the kinetics of type 2 cytokine production. Exogenous IL-6, IL-5, IL-1, and TNF-alpha enhanced the expression of T1/ST2 on Th2 cells, and IL-6 was by far most effective in this regard. However, the expression of T1/ST2 did not depend on the presence of IL-6 and was also detected in IL-6-deficient mice. Most important, cross-linking of T1/ST2 provided a costimulatory signal for Th2 but not Th1 cells and directly induced proliferation and type 2 cytokine production. Thus, T1/ST2 is not only a Th2 cell marker but also plays an important role in the activation of Th2 cells.

The expanding B7 superfamily: increasing complexity in costimulatory signals regulating T cell function

Upon encounter with specific antigen, naïveT helper precursor (THP) cells become activated. This event is regulated not only by engagement of the T cell receptor (TCR) with peptide presented in the context of major histocompatibility complex (MHC) class II molecules but by a number of costimulatory signals. CD28 engagement by B7-1 and B7-2 on resting THP cells provides a critical signal for initial cell cycle progression, interleukin 2 production and clonal expansion. However, largely as a consequence of the unraveling of the human genome, it is becoming clear that B7-1 and B7-2 are part of a larger family T of related counter-receptors that play an essential role in regulating the fate of primed, rather then resting,THP cells. These molecules play an important sequential role and act, together with B7-1- and B7-2-primed T cells, in the acquisition of effector function and/or tolerance induction.

Induction of type 2 activity in adult human CD8(+) T cells by repeated stimulation and IL-4

Repeated administration or chronic presence of antigen during CD4(+) T cell activation and a cytokine milieu enriched in IL-4 favour the generation and maintenance of a T(h)2 population. However, there is little data on how these factors affect adult human CD8(+) T cell functions. We established in vitro conditions to culture purified human CD8(+) T cells, and investigated how repeated stimulation and exogenous IL-4 modulated their functions. Repeated TCR-CD3 stimulation of CD8(+) T cells increased the number of CD25-, CD30- and CD40 ligand-expressing cells, and their capacity to secrete IL-4 and IL-5. In addition, repeatedly stimulated CD8(+) T cells had cytotoxic activity and provided help to resting B cells for IgE synthesis. The presence of exogenous IL-4 during repeated stimulation further increased the number of CD25(+) and CD30(+) CD8(+) T cells, up-regulated the number of IL-5(+) cells, and increased IL-5 levels released. These observations demonstrate that repeated TCR-CD3 stimulation of normal human CD8(+) T cells favoured the growth of cells with a type 2 phenotype and that this was further amplified by the presence of IL-4. These mechanisms may be important in virus-induced lung eosinophilic inflammation in healthy subjects and virus-induced exacerbations of asthma.

Resolution of bronchial hyperresponsiveness and pulmonary inflammation is associated with IL-3 and tissue leukocyte apoptosis

We have used two models of murine pulmonary inflammation to investigate the signals responsible for the resolution of bronchial hyperresponsiveness (BHR). Both protocols involved two sensitizations with OVA followed by serial aerosolized challenge with OVA. We determined that administration of the second sensitization by aerosol (model A) was associated with a transient response, whereas administration by the i.p. route (model B) induced a sustained response, in the form of BHR and eosinophilia. This difference in kinetics was due solely to the route of the second Ag administration and was not associated with Ag dose or adjuvant. Differences in kinetics of lung eosinophilia/BHR were shown to be independent of IgE levels and IL-4 or IL-5. However, IL-3 levels in model A closely correlated with the rate of leukocyte clearance by apoptosis and were observed concomitant with a decline in BHR. Blockage of IL-3 in model B increased leukocyte apoptosis but reduced tissue eosinophilia and BHR. The use of mouse models in which a single different administration of allergen is associated with a failure/success to resolve inflammation and BHR by 72 h postchallenge indicates a link between IL-3 production, leukocyte apoptosis, and BHR responses.

Cutting edge: the related molecules CD28 and inducible costimulator deliver both unique and complementary signals required for optimal T cell activation

Optimal T cell activation requires engagement of CD28 with its counterligands B7-1 and B7-2. Inducible costimulator (ICOS) is the third member of the CD28/CTLA4 family that binds a B7-like protein, B7RP-1. Administration of ICOS-Ig attenuates T cell expansion following superantigen (SAg) administration, but fails to regulate either peripheral deletion or anergy induction. ICOS-Ig, but not CTLA4-Ig, uniquely regulates SAg-induced TNF-alpha production, whereas IL-2 secretion is modulated by CTLA4-Ig, but not ICOS-Ig. In contrast, both ICOS and CD28 are required for complete attenuation of IL-4 production. Our data suggest that ICOS and CD28 regulate T cell expansion and that ligation of either CD28 or ICOS can either uniquely regulate cytokine production (IL-2/TNF-alpha) or synergize for optimal cytokine production (IL-4) after SAg administration.

Non-redundant functional groups of chemokines operate in a coordinate manner during the inflammatory response in the lung

The understanding of the relative contribution of particular chemokines to the selective accumulation of leukocyte subsets to an organ site during an inflammatory response is made difficult by the simultaneous presence of multiple chemokines with partially overlapping functions at the inflammatory site. The study of several chemokine pathways (expression and function) during the development of a mouse model of allergic airway disease (AAD) has revealed differential expression regulation with distinct cellular sources for individual chemokines with functional bias for the recruitment/localization of regulatory and/or effector leukocyte subsets. In the present review, we propose that distinct functional groups of chemokines co-operate to generate the complete inflammatory response in the lung during AAD. We will also extend these concepts to the specific recruitment of a key cellular subset such as T helper type 2 (Th2) lymphocytes. We propose that the long term recruitment of antigen-specific Th2 cells to target organs, such as airways during chronic lung inflammation, is the result the sequential involvement of several chemotactic axes. Specifically, the CCR3/eotaxin and the CCR4/MDC pathway act in a coordinated co-operative manner, with the CCR3/eotaxin pathway being critical in the acute/early stages of a response, followed by the CCR4/MDC pathway, which ultimately dominates in the recruitment of antigen-specific Th2 cells. Other chemokines/receptors participate in this process possibly by amplifying/priming the Th2 recruitment response.

Biotherapeutic targets for the treatment of allergic airway disease

T cells are critical mediators of inflammation and as such, their migration to inflammatory sites is a tightly controlled process involving a complex series of molecules expressed by a variety of cell types. As our appreciation of the mechanisms governing T cell surveillance, activation, differentiation, and subsequent homing to sites of inflammation has advanced, the opportunity to develop novel therapeutic agents that modulate the immune system has increased. Importantly, the possibility of specifically targetting subpopulations of effector cells raises the exciting potential for the development of novel agents that selectively modify the immune response to allergens, without resulting in generalized immune suppression.

Myeloid dendritic cells induce Th2 responses to inhaled antigen, leading to eosinophilic airway inflammation

The aim of this study was to investigate whether dendritic cells (DCs) can induce sensitization to aeroallergen in a mouse model of allergic asthma. Ovalbumin-pulsed (OVA-pulsed) or unpulsed myeloid DCs that were injected into the airways of naive mice migrated into the mediastinal lymph nodes. When challenged 2 weeks later with an aerosol of OVA, activated CD4 and CD8 lymphocytes, eosinophils, and neutrophils were recruited to the lungs of actively immunized mice. These CD4(+) lymphocytes produced predominantly IL-4 and IL-5 but also IFN-gamma, whereas CD8(+) lymphocytes produced predominantly IFN-gamma. Histological analysis revealed perivascular and peribronchial eosinophilic infiltrates and goblet cell hyperplasia. Studies in IL-4(-/-) and CD28(-/-) mice revealed that production of IL-4 by host cells and provision of costimulation to T cells by DCs were critical for inducing the response. Lung CD4(+) T cells strongly expressed the Th2 marker T1/ST2, and signaling through this molecule via a ligand expressed on DCs was essential for the establishment of airway eosinophilia. These data demonstrate that DCs in the airways induce sensitization to inhaled antigen and that molecules expressed on the surface of these cells are critical for the development of Th2-dependent airway eosinophilia.

Inducible costimulator protein (ICOS) controls T helper cell subset polarization after virus and parasite infection

It has been shown that certain pathogens can trigger efficient T cell responses in the absence of CD28, a key costimulatory receptor expressed on resting T cells. Inducible costimulator protein (ICOS) is an inducible costimulator structurally and functionally related to CD28. Here, we show that in the absence of CD28 both T helper cell type 1 (Th1) and Th2 responses were impaired but not abrogated after infection with lymphocytic choriomeningitis virus (LCMV), vesicular stomatitis virus (VSV), and the nematode Nippostrongylus brasiliensis. Inhibition of ICOS in CD28-deficient mice further reduced Th1/Th2 polarization. Blocking of ICOS alone had a limited but significant capacity to downregulate Th subset development. In contrast, cytotoxic T lymphocyte (CTL) responses, which are regulated to a minor and major extent by CD28 after LCMV and VSV infection, respectively, remained unaffected by blocking ICOS. Together, our results demonstrate that ICOS regulates both CD28-dependent and CD28-independent CD4(+) subset (Th1 and Th2) responses but not CTL responses in vivo.

The CD28-related molecule ICOS is required for effective T cell-dependent immune responses

While CD28 is critical for expansion of naive T cells, recent evidence suggests that the activation of effector T cells is largely independent of CD28/B7. We suggest that ICOS, the third member of the CD28/CTLA-4 family, plays an important role in production of IL-2, IL-4, IL-5, and IFNgamma from recently activated T cells and contributes to T cell-dependent B help in vivo. Inhibition of ICOS attenuates lung mucosal inflammation induced by Th2 but not Th1 effector populations. Our data indicate a critical function for the third member of the CD28 family in T cell-dependent immune responses.

Critical involvement of the chemotactic axis CXCR4/stromal cell-derived factor-1 alpha in the inflammatory component of allergic airway disease

Stromal cell-derived factor-1alpha/beta (SDF-1alpha/beta) is phylogenetically a primitive chemokine widely expressed in a variety of tissues and cell types. This expression is detectable in the absence of stimuli provided by bacterial or viral infections and allergic or autoimmune disorders. Based on these and other findings, SDF-1alpha has not been considered an inflammatory chemokine, but, rather, has been believed to be involved in certain homeostatic processes, such as leukocyte recirculation. SDF-1alpha is a potent chemoattractant for lymphocytes and monocytes that mediates its activity via the chemokine receptor CXCR4. Study of the role of SDF-1alpha/CXCR4 in vivo during inflammation has been limited by the fact that transgenic mice that have been made deficient in either molecule die early in life due to developmental defects. The present study was aimed at evaluating the functional relevance of the SDF-1alpha/CXCR4 axis during an inflammatory process. Neutralizing Abs to CXCR4 reduced lung eosinophilia (bronchoalveolar lavage fluid and interstitium) by half, indicating that CXCR4-mediated signals contribute to lung inflammation in a mouse model of allergic airway disease (AAD). This reduction in inflammation was accompanied by a significant decrease in airway hyper-responsiveness. SDF-1alpha neutralization resulted in similar reduction in both lung allergic inflammation and airway hyper-responsiveness. Retroviral delivery of a CXCR4 cDNA to leukocytes resulted in greater inflammation when transduced mice were subjected to a mouse model of AAD. These results highlight that, although considered a noninflammatory axis, the involvement of CXCR4 and SDF-1alpha is critical during AAD, and this receptor and its ligand are potentially relevant in other inflammatory processes.

CC chemokine receptor (CCR)3/eotaxin is followed by CCR4/monocyte-derived chemokine in mediating pulmonary T helper lymphocyte type 2 recruitment after serial antigen challenge in vivo

Isolated peripheral blood CD4 cells from allergic individuals express CC chemokine receptor (CCR)3 and CCR4 after expansion in vitro. In addition, human T helper type 2 (Th2) cells polarized in vitro selectively express CCR3 and CCR4 at certain stages of activation/differentiation and respond preferentially to the ligands eotaxin and monocyte-derived chemokine (MDC). However, controversy arises when the in vivo significance of this distinct expression is discussed. To address the functional role of CCR3/eotaxin and CCR4/MDC during the in vivo recruitment of Th2 cells, we have transferred effector Th cells into naive mice to induce allergic airway disease. Tracking of these cells after repeated antigen challenge has established that both CCR3/eotaxin and CCR4/MDC axes contribute to the recruitment of Th2 cells to the lung, demonstrating the in vivo relevance of the expression of these receptors on Th2 cells. We have shown that involvement of the CCR3/eotaxin pathway is confined to early stages of the response in vivo, whereas repeated antigen stimulation results in the predominant use of the CCR4/MDC pathway. We propose that effector Th2 cells respond to both CCR3/eotaxin and CCR4/MDC pathways initially, but that a progressive increase in CCR4-positive cells results in the predominance of the CCR4/MDC axis in the long-term recruitment of Th2 cells in vivo.

Fas-induced death of a murine pulmonary epithelial cell line: modulation by inflammatory cytokines

Here we report that a murine pulmonary epithelial cell line (LA-4) expresses Fas (CD95) under resting conditions. Exposure of untreated cells to an anti-Fas monoclonal antibody induces apoptosis in a time- and dose-dependent fashion as revealed by cell viability and by propidium iodide staining followed by FACS analysis. Fas surface expression was increased, in a time-dependent fashion, by the inflammatory cytokines IL-1beta and TNF-alpha. Other inflammatory mediators such as IFN-gamma or endothelin-1 were without any effect. This increase in Fas expression was associated with an increase in sensitivity to anti-Fas-induced apoptosis of LA-4 cells. IL-4, which is known to induce CD95 resistance in other cell types, did not protect LA-4 cells against anti-CD95-induced cell death. These results suggest that Fas-induced apoptosis of epithelial cells may contribute to the epithelial shedding observed in asthmatic airways.

Crucial role of the interleukin 1 receptor family member T1/ST2 in T helper cell type 2-mediated lung mucosal immune responses

T1/ST2 is an orphan receptor of unknown function that is expressed on the surface of murine T helper cell type 2 (Th2), but not Th1 effector cells. In vitro blockade of T1/ST2 signaling with an immunoglobulin (Ig) fusion protein suppresses both differentiation to and activation of Th2, but not Th1 effector populations. In a nascent Th2-dominated response, anti-T1/ST2 monoclonal antibody (mAb) inhibited eosinophil infiltration, interleukin 5 secretion, and IgE production. To determine if these effects were mediated by a direct effect on Th2 cells, we next used a murine adoptive transfer model of Th1- and Th2-mediated lung mucosal immune responses. Administration of either T1/ST2 mAb or T1/ST2-Ig abrogated Th2 cytokine production in vivo and the induction of an eosinophilic inflammatory response, but failed to modify Th1-mediated inflammation. Taken together, our data demonstrate an important role of T1/ST2 in Th2-mediated inflammatory responses and suggest that T1/ST2 may prove to be a novel target for the selective suppression of Th2 immune responses.

Mouse monocyte-derived chemokine is involved in airway hyperreactivity and lung inflammation

The cloning, expression, and function of the murine (m) homologue of human (h) monocyte-derived chemokine (MDC) is reported here. Like hMDC, mMDC is able to elicit the chemotactic migration in vitro of activated lymphocytes and monocytes. Among activated lymphocytes, Th2 cells were induced to migrate most efficiently. mMDC mRNA and protein expression is modulated during the course of an allergic reaction in the lung. Neutralization of mMDC with specific Abs in a model of lung inflammation resulted in prevention of airway hyperreactivity and significant reduction of eosinophils in the lung interstitium but not in the airway lumen. These data suggest that mMDC is essential in the transit/retention of leukocytes in the lung tissue rather than in their extravasation from the blood vessel or during their transepithelial migration into the airways. These results also highlight the relevance of factors, such as mMDC, that regulate the migration and accumulation of leukocytes within the tissue during the development of the key physiological endpoint of asthma, airway hyperreactivity.

T1/ST2 expression is enhanced on CD4+ T cells from schistosome egg-induced granulomas: analysis of Th cell cytokine coexpression ex vivo

Th cells are categorized into subsets based on the cytokine production of in vitro-differentiated Th populations. For in vivo-differentiated Th subsets, little is known about the heterogeneity of cytokine production in single cells. We recently described a molecule, T1/ST2, that is preferentially expressed on the surface of Th2 cells. Here we combined high-gradient magnetic cell separation with four-color single-cell cytometry to analyze simultaneously three intracellular cytokines and T1/ST2 surface expression on CD4+ cells from lungs containing granulomas induced by Schistosoma mansoni eggs. T1/ST2 was highly up-regulated on CD4+ T cells from hepatic granulomas and granulomatous lungs. T1/ST2+ cells from granulomatous lungs preferentially produced type 2 cytokines ex vivo. In the total CD4+ population, coexpression of type 1 and type 2 cytokines occurred frequently. However, such coproduction was drastically reduced in T1/ST2+ cells compared with T1/ST2- cells. Coexpression of type 1 and type 2 cytokines was also rare in cells simultaneously producing two cytokines of one type. These findings indicate that individual CD4+ T cells in vivo have different levels of commitment to a certain Th phenotype. Coexpression of two type 2 cytokines or production of one type 2 cytokine together with surface expression of T1/ST2 indicate advanced commitment to the Th2 phenotype.

Prolonged eosinophil accumulation in allergic lung interstitium of ICAM-2 deficient mice results in extended hyperresponsiveness

ICAM-2-deficient mice exhibit prolonged accumulation of eosinophils in lung interstitium concomitant with a delayed increase in eosinophil numbers in the airway lumen during the development of allergic lung inflammation. The ICAM-2-dependent increased and prolonged accumulation of eosinophils in lung interstitium results in prolonged, heightened airway hyperresponsiveness. These findings reveal an essential role for ICAM-2 in the development of the inflammatory and respiratory components of allergic lung disease. This phenotype is caused by the lack of ICAM-2 expression on non-hematopoietic cells. ICAM-2 deficiency on endothelial cells causes reduced eosinophil transmigration in vitro. ICAM-2 is not essential for lymphocyte homing or the development of leukocytes, with the exception of megakaryocyte progenitors, which are significantly reduced.

Eosinophils are not required to induce airway hyperresponsiveness after nematode infection

Eosinophilic inflammation of the airways is believed to play a central role in the pathogenesis of bronchial asthma. Inoculation of mice with the nematode Nippostrongylus brasiliensis induces pulmonary inflammation, characterized by a marked infiltration of eosinophils, subsequent to the migration of parasites through the lungs. Infection is associated with polarized Th2 responses in different strains of mice tested. Thus, this model may be useful to determine the relationship between established pulmonary eosinophilic inflammation, Th2 immune responses and airway changes in a nonallergic background. In the present study, we have used IL-5-deficient mice to evaluate the role of IL-5 in eosinophilic lung inflammation and airway hyperresponsiveness (AHR). In wild-type C57B/6 mice, infection with N. brasiliensis resulted in eosinophil accumulation, associated with extensive lung damage characterized by hemorrhage and alveolar wall destruction, and a strong AHR following methacholine treatment. In IL-5-deficient mice, eosinophil infiltration and the associated lung damage was abrogated. Nonetheless, AHR was unimpaired. Our results suggest that eosinophil accumulation plays a central role in lung damage but is not responsible for the induction of airway constriction following N. brasiliensis infection.

The coordinated action of CC chemokines in the lung orchestrates allergic inflammation and airway hyperresponsiveness

The complex pathophysiology of lung allergic inflammation and bronchial hyperresponsiveness (BHR) that characterize asthma is achieved by the regulated accumulation and activation of different leukocyte subsets in the lung. The development and maintenance of these processes correlate with the coordinated production of chemokines. Here, we have assessed the role that different chemokines play in lung allergic inflammation and BHR by blocking their activities in vivo. Our results show that blockage of each one of these chemokines reduces both lung leukocyte infiltration and BHR in a substantially different way. Thus, eotaxin neutralization reduces specifically BHR and lung eosinophilia transiently after each antigen exposure. Monocyte chemoattractant protein (MCP)-5 neutralization abolishes BHR not by affecting the accumulation of inflammatory leukocytes in the airways, but rather by altering the trafficking of the eosinophils and other leukocytes through the lung interstitium. Neutralization of RANTES (regulated upon activation, normal T cell expressed and secreted) receptor(s) with a receptor antagonist decreases significantly lymphocyte and eosinophil infiltration as well as mRNA expression of eotaxin and RANTES. In contrast, neutralization of one of the ligands for RANTES receptors, macrophage-inflammatory protein 1alpha, reduces only slightly lung eosinophilia and BHR. Finally, MCP-1 neutralization diminishes drastically BHR and inflammation, and this correlates with a pronounced decrease in monocyte- and lymphocyte-derived inflammatory mediators. These results suggest that different chemokines activate different cellular and molecular pathways that in a coordinated fashion contribute to the complex pathophysiology of asthma, and that their individual blockage results in intervention at different levels of these processes.

T1/ST2 is preferentially expressed on murine Th2 cells, independent of interleukin 4, interleukin 5, and interleukin 10, and important for Th2 effector function

T helper (Th) cells can be categorized according to their cytokine expression. The differential induction of Th cells expressing Th1 and/or Th2 cytokines is key to the regulation of both protective and pathological immune responses. Cytokines are expressed transiently and there is a lack of stably expressed surface molecules, significant for functionally different types of Th cells. Such molecules are of utmost importance for the analysis and selective functional modulation of Th subsets and will provide new therapeutic strategies for the treatment of allergic or autoimmune diseases. To this end, we have identified potential target genes preferentially expressed in Th2 cells, expressing interleukin (IL)-4, IL-5, and/or IL-10, but not interferon-gamma. One such gene, T1/ST2, is expressed stably on both Th2 clones and Th2-polarized cells activated in vivo or in vitro. T1/ST2 expression is independent of induction by IL-4, IL-5, or IL-10. T1/ST2 plays a critical role in Th2 effector function. Administration of either a mAb against T1/ST2 or recombinant T1/ST2 fusion protein attenuates eosinophilic inflammation of the airways and suppresses IL-4 and IL-5 production in vivo following adoptive transfer of Th2 cells.

Endothelin receptor antagonists inhibit antigen-induced lung inflammation in mice

In this study, we have examined the effect of endothelin (ET) receptor antagonists on lung granulocyte inflammation after antigen challenge in sensitized mice. The antagonists used were BQ-123, an ETA antagonist, BQ-788, an ETB antagonist, and SB209670, an ET(A&B) antagonist. Thirty minutes prior exposure to aerosolized ovalbumin, ET antagonists (50 pmol/mouse) were administered directly into the lungs of sensitized Balb/c mice via the intranasal route. BQ-123 and SB209670 significantly decreased eosinophil number in the bronchoalveolar lavage fluid by 47 and 68%, respectively. Both compounds also inhibited neutrophil infiltration into the lungs. In contrast, BQ-788 did not affect granulocyte infiltration. A similar inhibition of lung eosinophilia was also obtained with an anti-ET antibody applied via the intranasal route. BQ-123 and SB209670, but not BQ-788, significantly increased the production of interferon-gamma (Th1 cytokine) from purified lung Thy1.2+ cells without affecting interleukin-4 and interleukin-5 (Th2 cytokines) secretion. Furthermore, neutralizing antibody against interferon-gamma prevented the inhibitory effect of the ETA antagonist. Taken together, these results suggest an important pathophysiologic role for ET in the development of lung inflammation in asthma and highlight the potential of ET antagonists for the treatment of the disease.

Costimulation through B7-2 (CD86) is required for the induction of a lung mucosal T helper cell 2 (TH2) immune response and altered airway responsiveness

The recruitment of eosinophils into the airways after allergen exposure is dependent on interleukin (IL) 5 secreted from antigen-specific CD4+ T cells of the T helper cell (Th) 2 subset. However, while it is established that costimulation through CD28 is required for TCR-mediated activation and IL-2 production, the importance of this mechanism for the induction of a Th2 immune response is less clear. In the present study, we administered the fusion protein CTLA-4 immunoglobulin (Ig) into the lungs before allergen provocation to determine whether CD28/CTLA-4 ligands are required for allergen-induced eosinophil accumulation and the production of Th2 cytokines. Administration of CTLA-4 Ig inhibited the recruitment of eosinophils into the lungs by 75% and suppressed IgE in the bronchoalveolar lavage fluid. CTLA-4 Ig also inhibited the production of IL-4, IL-5, and IL-10 by 70-80% and enhanced interferon-gamma production from CD3-T cell receptor-activated lung Thy1.2+ cells. Allergen exposure upregulated expression of B7-2, but not B7-1, on B cells from the lung within 24 h. Moreover, airway administration of an anti-B7-2 monoclonal antibody (mAb) inhibited eosinophil infiltration, IgE production, and Th2 cytokine secretion comparable in magnitude to that observed with CTLA-4 Ig. Treatment with an anti-B7-1 mAb had a small, but significant effect on eosinophil accumulation, although was less effective in inhibiting Th2 cytokine production. The anti-B7-2, but not anti-B7-1, mAb also inhibited antigen-induced airway hyperresponsiveness in vivo. In all of the parameters assessed, the combination of both the anti-B7-1 and anti-B7-2 mAb was no more effective than anti-B7-2 mAb treatment alone. We propose that strategies aimed at inhibition of CD28 interactions with B7-2 molecules may represent a novel therapeutic target for the treatment of lung mucosal allergic inflammation.

IL-4 differentiates naive CD8+ T cells to a "Th2-like" phenotype: a link between viral infections and bronchial asthma

Viral infections of the lung have been postulated to be a major factor in the etiology of bronchial asthma, a disease characterized by eosinophilic inflammation of the airways. In addition, upper respiratory tract infection in asthmatic individuals results in an exacerbation of the disease. Nevertheless, the mechanisms by which viral infection leads to disease exacerbation are poorly understood. CD8+ T cells play an important role in the host defense responses against viral infection, although to date, there are no reports to suggest that CD8+ T cells play any role in eosinophil recruitment. In the present study, we report that CD8+ T cells activated by either immobilized CD3 mAb or specific antigen can switch to a phenotype that produces Th2 cytokines and secretes less IFN-gamma. Moreover, in vivo, if a lung mucosal Th2 immune response exists, then antigen-specific activation of CD8 cells results in the development of lung eosinophilic inflammation mediated by the secretion of IL-5 from CD8+ T cells. These results may explain the link between viral infections and bronchial asthma, as this IL-4-dependent switch to CD8+ T cells to IL-5 secretion may not only exacerbate asthma by recruiting eosinophils into the lungs, but the impaired IFN-gamma production may also lead to delayed viral clearance.

Cloning and characterization of a novel murine macrophage inflammatory protein-1 alpha receptor

We have cloned a novel CC chemokine receptor cDNA from mouse thymus. The deduced amino acid sequence shows 74% identity to the human monocyte chemotactic protein (MCP)-1 receptor (CC CKR-2b) and 54% to a recently cloned murine macrophage inflammatory protein (MIP)-1alpha receptor (Gao, J. L., and Murphy, P. M.(1995) J. Biol. Chem. 270, 17494-17501). Northern blot analysis of mouse tissues showed that the mRNA was also expressed in heart, spleen and liver, and to a lesser extent in lung and brain. The rank order of CC chemokine competition for 125I-labeled human RANTES (regulated on activation, normal T-cell expressed and secreted) binding to human embryonic kidney (HEK) 293 cells stably transfected with the receptor cDNA was murine MIP-1alpha >> human MIP-1beta > human RANTES > murine RANTES > murine MIP-1beta > human MCP-2 > murine MCP-1 (JE) > human MIP-1alpha > human MCP-3 > human MCP-1. Of the chemokines tested, only murine MIP-1alpha, human and murine MIP-1beta and RANTES, human MCP-2, and JE were able to induce mobilization of intracellular Ca2+ from fura-2-loaded HEK 293 cells expressing the receptor. These results suggest that this receptor functions as a high affinity murine MIP-1alpha receptor; however, it is likely to be an important target for the biological activities of several CC chemokines in mouse.

Mice lacking the IFN-gamma receptor have impaired ability to resolve a lung eosinophilic inflammatory response associated with a prolonged capacity of T cells to exhibit a Th2 cytokine profile

To investigate the modulatory role of IFN-gamma on the induction and maintenance of Th2 mucosal immunity in vivo, experiments were performed in mice lacking the IFN-gamma R. Aerosol OVA challenge of immunized wild-type mice resulted in an infiltration of eosinophils into the lung, associated with the ex vivo production of Th2 cytokines (IL-4 and IL-5) from purified lung Thy1.2+ cells stimulated via the CD3/TCR complex. However, while immunized IFN-gamma R-deficient mice exhibited elevated levels of IgE, IgG1, and reduced levels of IgG2a compared with wild-type mice, there was no difference in the recruitment of eosinophils into the lung or the production of IL-4 and IL-5 from lung T cells on day 3. In contrast, up to 2 mo after a single Ag challenge, eosinophils were still present in the lungs of IFN-gamma R-deficient, but not wild-type, mice. Likewise, lung-derived T cells from IFN-gamma R-deficient mice produced higher levels of IL-4 and IL-5, both at 1 and 2 mo after OVA challenge compared with T cells from wild-type mice. We conclude that endogenous IFN-gamma regulates the humoral isotype Ab pattern, but does not modulate the commitment of T cells to a Th2 phenotype in vivo or the acute infiltration of eosinophils to the lung. However, in the absence of IFN-gamma-mediated signaling, there is a transition from a spontaneously resolving to a persisting eosinophilic inflammation of the lungs, associated with a sustained capacity of lung T cells to secrete a Th2 cytokine profile.

Mice lacking the IFN-gamma receptor have impaired ability to resolve a lung eosinophilic inflammatory response associated with a prolonged capacity of T cells to exhibit a Th2 cytokine profile

To investigate the modulatory role of IFN-gamma on the induction and maintenance of Th2 mucosal immunity in vivo, experiments were performed in mice lacking the IFN-gamma R. Aerosol OVA challenge of immunized wild-type mice resulted in an infiltration of eosinophils into the lung, associated with the ex vivo production of Th2 cytokines (IL-4 and IL-5) from purified lung Thy1.2+ cells stimulated via the CD3/TCR complex. However, while immunized IFN-gamma R-deficient mice exhibited elevated levels of IgE, IgG1, and reduced levels of IgG2a compared with wild-type mice, there was no difference in the recruitment of eosinophils into the lung or the production of IL-4 and IL-5 from lung T cells on day 3. In contrast, up to 2 mo after a single Ag challenge, eosinophils were still present in the lungs of IFN-gamma R-deficient, but not wild-type, mice. Likewise, lung-derived T cells from IFN-gamma R-deficient mice produced higher levels of IL-4 and IL-5, both at 1 and 2 mo after OVA challenge compared with T cells from wild-type mice. We conclude that endogenous IFN-gamma regulates the humoral isotype Ab pattern, but does not modulate the commitment of T cells to a Th2 phenotype in vivo or the acute infiltration of eosinophils to the lung. However, in the absence of IFN-gamma-mediated signaling, there is a transition from a spontaneously resolving to a persisting eosinophilic inflammation of the lungs, associated with a sustained capacity of lung T cells to secrete a Th2 cytokine profile.

Central role of immunoglobulin (Ig) E in the induction of lung eosinophil infiltration and T helper 2 cell cytokine production: inhibition by a non-anaphylactogenic anti-IgE antibody

Elevated levels of immunoglobulin (Ig) E are associated with bronchial asthma, a disease characterized by eosinophilic inflammation of the airways. Activation of antigen-specific T helper (Th) 2 cells in the lung with the subsequent release of interleukin (IL) 4 and IL-5 is believed to play an important role in the pathogenesis of this disease. In this study, we have used a non-anaphylactogenic anti-mouse-IgE antibody to investigate the relationship between IgE, airway eosinophil infiltration, and the production of Th2 cytokines. Immunization of mice with house dust mite antigen increased serum levels of IgE and IgG. Antigen challenge of immunized but not control mice induced an infiltration of eosinophils in the bronchoalveolar lavage associated with the production of IL-4 and IL-5 from lung purified Thy1.2+ cells activated through the CD3-T cell receptor complex. Administration of the anti-IgE monoclonal antibody (mAb) 6h before antigen challenge neutralized serum IgE but not IgG and inhibited the recruitment of eosinophils into the lungs and the production of IL-4 and IL-5 but not interferon gamma. Studies performed using an anti-CD23 mAb, CD23 deficient and mast cell deficient mice suggest that anti-IgE mAb suppresses eosinophil infiltration and Th2 cytokine production by inhibiting IgE-CD23-facilitated antigen presentation to T cells. Our results demonstrate that IgE-dependent mechanisms are important in the induction of a Th2 immune response and the subsequent infiltration of eosinophils into the airways. Neutralization of IgE, for example, non-anaphylactogenic anti-IgE mAbs may provide a novel therapeutic approach to the treatment of allergic airway disease.

Comparison of Na+-dependent glutamate transport activity in synaptosomes, C6 glioma, and Xenopus oocytes expressing excitatory amino acid carrier 1 (EAAC1)

Several subtypes of sodium-dependent high affinity (SDHA) glutamate transporters have been pharmacologically differentiated in brain tissue. Recently, four distinct cDNAs (EAAC1, GLT1, GLAST, and EAAT4) encoding Na+-dependent glutamate transporters have been isolated, but the properties of some of these transporters do not fully match the properties of transport observed in brain tissue or astrocyte-enriched cultures. The purpose of the current investigation was to determine whether the pharmacological properties of EAAC1 parallel those observed in cortical or cerebellar synaptosomes, C6 glioma, or primary astrocyte-enriched cultures. EAAC1 cRNA was expressed in Xenopus oocytes, an expression system with no detectable endogenous Na+-dependent glutamate transport activity. EAAC1-mediated glutamate transport was >98% Na+ dependent, and the transport was saturable and consistent with a single site. Glutamate transport activates in EAAC1-injected oocytes and C6 glioma have similar Km values for glutamate (Km = 15-24 microM) and Na+ (apparent Km = 35-50mM), and these values markedly differ from those observed in rat synaptosomes (glutamate, Km = 1-5 microM; Na+, Km = 13-20 mM). Several excitatory amino acid analogues were tested as inhibitors of L-[3H] glutamate transport in oocytes expressing EAAC1 cRNA. The potencies of several compounds for inhibition of EAAC1-mediated transport differed from those previously observed in cerebellar synaptosomes and astrocyte-enriched cultures. Although EAAC1-mediated transport and cortical synaptosomal transport have similar pharmacological profiles, five excitatory amino acid analogues were > or= 3-fold more potent as inhibitors of transport into cortical synaptosomes than of transport into EAAC1-injected oocytes. For example, L-trans-pyrrolidine-2,4-dicarboxylate was approximately 5-fold more potent in cortical synaptosomes, and dihydrokainate was approximately 10-fold more potent in cortical synaptosomes than in EAAC1-injected oocytes. In contrast, all of the compounds examined inhibit transport observed in C6 glioma wtih potencies similar to that observed in oocytes injected with EAAC1 cRNA. Consistent with these data, C6 glioma expressed EAAC1- but not GLT1- and GLAST-like immunoreactivity. Although this immunoreactivity migrated as proteins of slightly different molecular masses in each system, treatment with N-glycosidase F shifted all proteins to a molecular mass consistent with that predicted from the cDNA sequence. In cortical synaptosomes, EAAC1-, GLT1-, and GLAST-like immunoreactives were apparent. These results indicate that (i) EAAC1 but not GLAST or GLT1 transporters are expressed in C6 glioma, (ii) synaptosomes contain a heterogeneous population of transporters, (iii) EAAC1 does not account for the pharmacology previously observed in cortical synaptosomes, and (iv) based on the pharmacology and tissue distribution of EAAC1, GLT1, GLAST, and EAAT4, it appears that there are additional glutamate transporter subtypes.

Mouse Eotaxin expression parallels eosinophil accumulation during lung allergic inflammation but it is not restricted to a Th2-type response

A model of lung eosinophilia based on the repeated exposure of mice to aerosolized OVA has been used to identify C-C chemokine genes expressed at stages of massive eosinophil infiltration. We describe the identification and cloning of a cDNA that encodes a mouse C-C chemokine with 68% amino acid identity to guinea pig Eotaxin. The recombinant protein encoded by this gene displays potent and specific chemotactic activity for eosinophils, both in vivo and in vitro. Its mRNA levels parallel the kinetics of eosinophil accumulation in the lung during the experimentally induced eosinophilia and it is mainly produced by type I alveolar epithelial cells. The mRNA expression of mouse Eotaxin is not restricted to Th2 T cells in vitro and is independent of the development of a Th2-type response during N. brasiliensis infection, in vivo.

Activation of the Fas receptor on lung eosinophils leads to apoptosis and the resolution of eosinophilic inflammation of the airways

While considerable progress has been made in understanding the events by which eosinophils accumulate in various pathophysiological conditions, the mechanisms controlling the resolution of eosinophilic inflammation are poorly understood. In the present study, we demonstrate that lung eosinophils obtained by bronchoalveolar lavage (BAL) after aerosol allergen provocation of immunized mice expressed the Fas receptor. Stimulation of purified eosinophils in vitro with a monoclonal anti-Fas mAb (1 ng-1 microg/ml) induced a dose/time dependent loss of cell viability from 24-72 h. Measurement of DNA fragmentation with propidium iodide confirmed that anti-Fas induced eosinophil death by apoptosis. While incubation with IL-3, IL-5, or GM-CSF prevented spontaneous apoptosis, these factors failed to prevent anti-Fas induced apoptosis. Administration of anti-Fas mAb to the lungs after the induction of a lung eosinophilia increased the number of peroxidase positive macrophages in BAL fluid 4-12 h later which was followed by a marked reduction in the number of eosinophils in the airways. Importantly, Fas-mediated resolution of eosinophilic inflammation occurred in the absence of any overt secondary inflammatory changes in the lungs. We speculate that defects in this pathway may at least in part explain the chronic eosinophilic inflammation often observed in the lungs of asthmatic individuals.

Interleukin-4 is required for the induction of lung Th2 mucosal immunity

Aerosol antigen challenge of ovalbumin-sensitized mice induced an eosinophilic airway inflammation that was dependent on interleukin (IL)-5 and CD4+, but not CD8+, T lymphocytes. The involvement of the Th2 phenotype of CD4+ T cells was supported by demonstrating that FACS-sorted purified lung T cells from sensitized, but not control, mice produced IL-4, IL-5, and IL-10 after activation of the CD3/TCR complex. To determine the role of IL-4 in this process, we used mice in which the gene for IL-4 was deleted by homologous recombination. Antigen challenge of IL-4 gene-targeted mice resulted in a marked attenuation of eosinophilic inflammation and IL-5 secretion. To more fully understand the time when IL-4 was involved, we administered a neutralizing anti-IL-4 antibody (11B11) either immediately before antigen challenge or during immunization. Inhibition of IL-4 before antigen challenge had little effect on antigen-induced eosinophil infiltration. However, when 11B11 was administered during immunization, there was a marked reduction in eosinophil infiltration. Cross-linking of the CD3/TCR complex of FACS-sorted lung T cells revealed that only when anti-IL-4 was administered during immunization was there an inhibition of T cell-derived IL-5 and IgE production. These results suggest that IL-4 is central both to the induction of a local Th2 response and to the development of eosinophilic inflammation of the lung. Moreover, we suggest a sequential involvement of IL-4 and IL-5, with IL-4 committing naive T cells to a Th2 phenotype which upon activation by aerosol provocation secrete IL-5, resulting in eosinophil accumulation.

Human eosinophil-granule major basic protein and synthetic polycations induce airway hyperresponsiveness in vivo dependent on bradykinin generation

In the current series of experiments we investigated the role of bradykinin in airway hyperresponsiveness induced by human eosinophil-granule major basic protein (MBP). Bronchoalveolar lavage was performed after intratracheal instillation of MBP or poly-L-lysine in anesthetized, intubated rats, and levels of immunoreactive kinins and kallikrein-like activity were determined. Both MBP and poly-L-lysine induced a three- and eightfold increase in levels of kallikrein-like activity and i-kinins, respectively. To determine whether kinin production is required for the development of airway hyperresponsiveness induced by cationic proteins, dose-response curves to methacholine were constructed before and 1 h after intratracheal instillation of either MBP or poly-L-lysine (100 micrograms). MBP and poly-L-lysine induced an increase in airway responsiveness, which was inhibited by pretreatment with a selective BK-2 receptor antagonist, NPC 17713 (250 micrograms/ml). Our results demonstrate that MBP and poly-L-lysine activate kallikrein and stimulate the generation of i-kinins in vivo, an effect that may be related to the cationic charge of these proteins. Furthermore, the ability of these proteins to increase airway responsiveness appears to be dependent on the generation of i-kinins.

Tight bounds on the sensitivity of generalised semi-Markov processes with a single generally distributed lifetime

There are some generalised semi-Markov processes (GSMP) which are insensitive, that is the value of some performance measures for the system depend only on the mean value of lifetimes and not on their actual distribution. In most cases this is not true and a performance measure can take on a number of values depending on the lifetime distributions. In this paper we present a method for finding tight bounds on the sensitivity of performance measures for the class of GSMPs with a single generally distributed lifetime. Using this method we can find upper and lower bounds for the value of a function of the stationary distribution as the distribution of the general lifetime ranges over a set of distributions with fixed mean. The method is applied to find bounds on the average queue length of the Engset queue and the time congestion in the GI/M/n/n queueing system.