Airway eosinophils: allergic inflammation recruited professional antigen-presenting cells

The capacity of airway eosinophils, potentially pertinent to allergic diseases of the upper and lower airways, to function as professional APCs, those specifically able to elicit responses from unprimed, Ag-naive CD4(+) T cells has been uncertain. We investigated whether airway eosinophils are capable of initiating naive T cell responses in vivo. Eosinophils, isolated free of other APCs from the spleens of IL-5 transgenic mice, following culture with GM-CSF expressed MHC class II and the costimulatory proteins, CD40, CD80, and CD86. Eosinophils, incubated with OVA Ag in vitro, were instilled intratracheally into wild-type recipient mice that adoptively received i.v. infusions of OVA Ag-specific CD4(+) T cells from OVA TCR transgenic mice. OVA-exposed eosinophils elicited activation (CD69 expression), proliferation (BrdU incorporation), and IL-4, but not IFN-gamma, cytokine production by OVA-specific CD4(+) T cells in paratracheal lymph nodes (LN). Exposure of eosinophils to lysosomotropic NH(4)Cl, which inhibits Ag processing, blocked each of these eosinophil-mediated activation responses of CD4(+) T cells. By three-color fluorescence microscopy, OVA Ag-loaded eosinophil APCs were physically interacting with naive OVA-specific CD4(+) T cells in paratracheal LN after eosinophil airway instillation. Thus, recruited luminal airway eosinophils are distinct allergic "inflammatory" professional APCs able to activate primary CD4(+) T cell responses in regional LNs.     

Cross presentation of antigen on MHC class II via the draining lymph node after corneal transplantation in mice

We investigated Ag trafficking from the cornea and T effector cell activation in secondary lymphoid tissue after corneal transplantation. In preliminary experiments, the central cornea was shown to contain a population of CD45(+), CD11b(+), CD11c- cells, with a few MHC class II(+) cells, and F4/80(+) cells. However, MHC class II(+) passenger leukocytes in donor cornea after allografting did not traffic to the draining lymph node. Instead, Ag (plasmid) delivered to the eye via the donor cornea during allograft was detected in host CD11c(+) and F4/80(+) APC in the draining lymph nodes and spleen. The earliest detection of APC-associated Ag was at 6 h in the draining lymph node and 24 h in the spleen. After 48 h Ag was not detected in the draining lymph node but was still present in the spleen. Ag applied to the donor corneal epithelium before allografting induced Ag-specific T cell activation and expansion in the draining lymph node with a peak response at 4-6 days, indicating that cross-presentation of Ag had occurred. We conclude therefore, that Ag is transported from the donor cornea within host APC and that this event occurs within hours after grafting. Ag is cross-presented to host CD4(+) T cells on MHC class II and leads to the activation of Ag-specific effector T cells and clonal expansion in the draining lymph node.     

Restricted aeroallergen access to airway mucosal dendritic cells in vivo limits allergen-specific CD4+ T cell proliferation during the induction of inhalation tolerance

Chronic innocuous aeroallergen exposure attenuates CD4(+) T cell-mediated airways hyperresponsiveness in mice; however, the mechanism(s) remain unclear. We examined the role of airway mucosal dendritic cell (AMDC) subsets in this process using a multi-OVA aerosol-induced tolerance model in sensitized BALB/c mice. Aeroallergen capture by both CD11b(lo) and CD11b(hi) AMDC and the delivery of OVA to airway draining lymph nodes by CD8α(-) migratory dendritic cells (DC) were decreased in vivo (but not in vitro) when compared with sensitized but nontolerant mice. This was functionally significant, because in vivo proliferation of OVA-specific CD4(+) T cells was suppressed in airway draining lymph nodes of tolerized mice and could be restored by intranasal transfer of OVA-pulsed and activated exogenous DC, indicating a deficiency in Ag presentation by endogenous DC arriving from the airway mucosa. Bone marrow-derived DC Ag-presenting function was suppressed in multi-OVA tolerized mice, and allergen availability to airway APC populations was limited after multi-OVA exposure, as indicated by reduced OVA and dextran uptake by airway interstitial macrophages, with diffusion rather than localization of OVA across the airway mucosal surface. These data indicate that inhalation tolerance limits aeroallergen capture by AMDC subsets through a mechanism of bone marrow suppression of DC precursor function coupled with reduced Ag availability in vivo at the airway mucosa, resulting in limited Ag delivery to lymph nodes and hypoproliferation of allergen-specific CD4(+) T cells.     

In situ analysis reveals physical interactions between CD11b+ dendritic cells and antigen-specific CD4 T cells after subcutaneous injection of antigen

In situ staining techniques were used to visualize physical interactions between dendritic cell subsets and naive Ag-specific CD4 T cells in the lymph node. Before injection of Ag, CD8(+) dendritic cells and naive OVA-specific CD4 T cells were uniformly distributed throughout the T cell-rich paracortex, whereas CD11b(+) dendritic cells were located mainly in the outer edges of the paracortex near the B cell-rich follicles. Many OVA-specific CD4 T cells were in contact with CD8(+) dendritic cells in the absence of OVA. Within 24 h after s.c. injection of soluble OVA, the OVA-specific CD4 T cells redistributed to the outer paracortex and interacted with CD11b(+), but not CD8(+) dendritic cells. This behavior correlated with the uptake of OVA and the presence of peptide-MHC complexes on the surface of CD11b(+) dendritic cells, and subsequent IL-2 production by the Ag-specific CD4 T cells. These results are consistent with the possibility that CD11b(+) dendritic cells play a central role in the activation of CD4 T cells in response to s.c. Ag.     

Inert 50-nm polystyrene nanoparticles that modify pulmonary dendritic cell function and inhibit allergic airway inflammation

Nanoparticles are being developed for diverse biomedical applications, but there is concern about their potential to promote inflammation, particularly in the lung. Although a variety of ambient, anthropogenic and man-made nanoparticles can promote lung inflammation, little is known about the long-term immunomodulatory effects of inert noninflammatory nanoparticles. We previously showed polystyrene 50-nm nanoparticles coated with the neutral amino acid glycine (PS50G nanoparticles) are not inflammatory and are taken up preferentially by dendritic cells (DCs) in the periphery. We tested the effects of such nanoparticles on pulmonary DC function and the development of acute allergic airway inflammation. Surprisingly, exposure to PS50G nanoparticles did not exacerbate but instead inhibited key features of allergic airway inflammation including lung airway and parenchymal inflammation, airway epithelial mucus production, and serum allergen-specific IgE and allergen-specific Th2 cytokines in the lung-draining lymph node (LN) after allergen challenge 1 mo later. PS50G nanoparticles themselves did not induce lung oxidative stress or cardiac or lung inflammation. Mechanistically, PS50G nanoparticles did not impair peripheral allergen sensitization but exerted their effect at the lung allergen challenge phase by inhibiting expansion of CD11c(+)MHCII(hi) DCs in the lung and draining LN and allergen-laden CD11b(hi)MHCII(hi) DCs in the lung after allergen challenge. PS50G nanoparticles further suppressed the ability of CD11b(hi) DCs in the draining LN of allergen-challenged mice to induce proliferation of OVA-specific CD4(+) T cells. The discovery that a defined type of nanoparticle can inhibit, rather than promote, lung inflammation via modulation of DC function opens the door to the discovery of other nanoparticle types with exciting beneficial properties.     

Cutting edge: Antigen is not required for the activation and maintenance of virus-specific memory CD8+ T cells in the lung airways

Respiratory virus infections establish a population of memory CD8(+) T cells in the lung airways that persist for months after infection. However, the relationship between Ag-specific memory T cells in the lung airways and the systemic memory T cell pool is not well understood. The majority of lung airway memory T cells express a highly activated phenotype (CD69(+)/CD127(-)), suggesting that recent Ag stimulation is required to drive T cell activation and recruitment to the lung airways. In this study, we demonstrate that the lung airway environment itself in the absence of cognate Ag alters the expression of acute activation markers such as CD69 and CD127 on memory CD8(+) T cells. Furthermore, the steady-state recruitment of virus-specific memory CD8(+) T cells to the lung airways from the circulation can occur without recent Ag stimulation. These findings alter the current perceptions concerning the contribution of Ag to the maintenance of peripheral T cell memory.     

The distribution of antigen in lymphoid tissues following its injection into the anterior chamber of the rat eye

Injection of Ag into the anterior chamber (AC) of the eye induces deviant immune responses. It has been proposed that Ag internalized by ocular APCs is presented in a tolerogenic fashion in the spleen. However, the nature and distribution of the Ag-bearing cells in the lymphoid organs remain unclear. Fluorescent-labeled Ag (dextran, BSA) injected into the AC of Lewis rats was detected in the subcapsular sinus of the right submandibular lymph nodes (LNs) and cervical LNs, the marginal zone of the spleen, and the medulla of the mesenteric LNs. In the spleen, Ag-bearing cells were CD1(+), CD11b(+), ED1(+), ED2(low), ED3(+), CD86(low), OX6(+), CD11c(-), ED5(-) and in the LNs were CD4(+), CD8(+), CD80(+), and OX41(+) suggesting these were lymphoid organ resident macrophages. These Ag-bearing macrophages were located adjacent to CD4(+) cells, CD8(+) cells, and NK cells in the LNs and spleen and to marginal zone B cells in the spleen. No interaction with gamma delta T cells was observed. The data demonstrates that Ag derived from the AC of the eye is mainly internalized by resident macrophages in the LNs and spleen which are ideally placed to interact with cells involved in the induction of deviant ocular immune responses. The extensive distribution of Ag in LNs draining the upper airway and gastrointestinal tracts, together with the phenotype of Ag-bearing cells in the lymphoid organs, suggests that Ag leaves the eye predominantly in a soluble form and implies other mechanisms of tolerance may contribute to ocular-specific immune responses.     

Rapid up-regulation of CXC chemokines in the airways after Ag-specific CD4+ T cell activation

Ag-specific activation of CD4(+) T cells is known to be causative for the cytokine production associated with lung allergy. Chemokine-induced leukocyte recruitment potentially represents a critical early event in Ag-induced lung inflammation. Whether Ag-specific, lung CD4(+) T cell activation is important in lung chemokine production is currently not clear. Using alphabeta-TCR transgenic BALB/c DO11.10 mice, we investigated the ability of Ag-specific CD4(+) T cell activation to induce lung chemokine production and leukocyte recruitment. Within 1 h of exposure of DO11. 10 mice to OVA aerosol, lung mRNA and protein for the neutrophil chemokines KC and macrophage inflammatory protein (MIP)-2 were greatly increased. Accordingly, neutrophils in the airways increased by >50-fold, and KC and MIP-2 proved to be functional because their neutralization significantly reduced airway neutrophilia. CD4(+) T cell activation was critical because CD4(+) but not CD8(+) T cell depletion reduced KC production, which correlated well with the previously observed inhibition of neutrophil influx after CD4(+) T cell depletion. In vitro studies confirmed that OVA-induced KC and MIP-2 production was conditional upon the interaction of CD4(+) T cells with APCs. A likely secondary mediator was TNF-alpha, and a probable source of these chemokines in the lung was alveolar macrophages. Thus, Ag-specific CD4(+) T cell activation in the lung leads to rapid up-regulation of neutrophil chemokines and the recruitment of neutrophils to the site of Ag exposure. This may be a key early event in the pathogenesis of Ag-induced lung inflammation.     

APCs in the anterior uveal tract do not migrate to draining lymph nodes

The migration of APCs from sites of infection and their maturation are critical elements in the generation of immune responses. However, the paths by which intraocular Ags migrate to draining lymph nodes are not known because the eye has limited lymphatic vessels. To date, only dendritic cells from the cornea and conjunctiva have been shown to emigrate. We demonstrate that phagocytic APCs in the anterior uveal tissues of the murine eye that ingest fluorescent latex beads do not migrate to regional lymph nodes. The beads are ingested in the uveal tract by cells expressing MHC class II, CD11c, or F4/80. Using intravital time-lapse videomicroscopy to monitor iris APC migration after anterior chamber injection of fluorescent Ag, fluorescently labeled APCs fail to move at multiple observation times, even in the presence of Ag and LPS. Whereas an as yet unidentified ocular nonphagocytic APC subset might migrate from the anterior uveal tissues, it is more probable that immune responses in the draining lymph nodes are engendered by soluble Ag escaping the eye through interstitial spaces. The inability of anterior uveal tissue APCs to migrate to lymph nodes may contribute to deviant immune responses that dominate after Ags are introduced into the anterior chamber.     

Dynamics of dendritic cell phenotype and interactions with CD4+ T cells in airway inflammation and tolerance

An emerging concept is that different types of dendritic cells (DCs) initiate different immune outcomes, such as tolerance vs inflammation. In this study, we have characterized the DCs from the lung draining lymph nodes of mice immunized for allergic airway inflammation or tolerance and examined their interactions with CD4(+) T cells. The DC population derived from tolerized mice was predominantly CD11c(+), B220(+), Gr-1(+), CD11b(-), and MHC class II(low), which resembled plasmacytoid-type DCs whereas DCs from the inflammatory condition were largely CD11c(+), B220(-), Gr-1(-), CD11b(+), and MHC class II(high) resembling myeloid-type DCs. The DCs from the tolerogenic condition were poor inducers of T cell proliferation. DCs from both conditions induced T cell IL-4 production but the T cells cultured with tolerogenic DCs were unresponsive to IL-4 as indicated by inhibition of STAT6 activation and expression of growth factor-independent 1, which has been recently shown to be important for STAT6-activated Th2 cell expansion. Our data suggest that airway tolerance vs inflammation is determined by the DC phenotype in lung draining lymph nodes.     

Airway eosinophils accumulate in the mediastinal lymph nodes but lack antigen-presenting potential for naive T cells

Asthma is characterized by infiltration of the airway wall with eosinophils. Although eosinophils are considered to be effector cells, recent studies have reported their ability to activate primed Th2 cells. In this study, we investigated whether eosinophils are capable of presenting Ag to unprimed T cells in draining lymph nodes (DLN) of the lung and compared this capacity with professional dendritic cells (DC). During development of eosinophilic airway inflammation in OVA-sensitized and challenged mice, CCR3(+) eosinophils accumulated in the DLN. To study their function, eosinophils were isolated from the bronchoalveolar lavage fluid of mice by sorting on CCR3(+)B220(-)CD3(-)CD11c(dim) low autofluorescent cells, avoiding contamination with other APCs, and were intratracheally injected into mice that previously received CFSE-labeled OVA TCR-transgenic T cells. Eosinophils did not induce divisions of T cells in the DLN, whereas DC induced on average 3.7 divisions in 45.7% of T cells. To circumvent the need for Ag processing or migration in vivo, eosinophils were pulsed with OVA peptide and were still not able to induce T cell priming in vitro, whereas DC induced vigorous proliferation. This lack of Ag-presenting ability was explained by the very weak expression of MHC class II on fresh eosinophils, despite expression of the costimulatory molecules CD80 and ICAM-1. This investigation does not support any role for airway eosinophils as APCs to naive T cells, despite their migration to the DLN at times of allergen exposure. DC are clearly superior in activating T cells in the DLN of the lung.     

Uptake of particulate antigens in a nonmammalian lung: phenotypic and functional characterization of avian respiratory phagocytes using bacterial or viral antigens

Major distinctive features of avian lungs are the absence of draining lymph nodes and alveoli and alveolar macrophages (MPhs). However, a large network of MPhs and dendritic cells (DCs) is present in the mucosa of the larger airways and in the linings of the parabronchi. For the modulation of respiratory tract immune responses, for example, by vaccination, a better understanding of Ag uptake in the chicken respiratory tract is needed. In this study, we provide detailed characterization of APCs in chicken lungs, including their functional in vivo activities as measured by the uptake of fluorescently labeled 1-μm beads that are coated with either LPS or inactivated avian influenza A virus (IAV) mimicking the uptake of bacterial or viral Ag. We identified different subsets of MPhs and DCs in chicken lungs, based on the expression of CD11, activation markers, and DEC205. In vivo uptake of LPS- and IAV-beads resulted in an increased percentage MHC class II(+) (MHC II(+)) cells and in the upregulation of CD40. The uptake of LPS-beads resulted in the upregulation of CD80 and MHC II on the cell surface, suggesting either uptake of LPS- and IAV-beads by different subsets of phagocytic cells or LPS-mediated differential activation. Differences in phagosomal acidification indicated that in chicken lungs the MHC II(+) and CD80(+) bead(+) cell population includes DCs and that a large proportion of beads was taken up by MPhs. LPS-bead(+) cells were present in BALT, suggesting local induction of immune responses. Collectively, we characterized the uptake of Ags by phagocytes in the respiratory tract of chickens.     

Lung CD25 CD4 regulatory T cells suppress type 2 immune responses but not bronchial hyperreactivity

To study the effects of chronic Ag deposition in the airway mucosa on CD4(+) T cell priming and subsequent airway disease, transgenic mice were generated that expressed OVA under the control of the surfactant protein C promoter. CD4 T cells from these mice were tolerant to OVA but this was overcome among spleen CD4 T cells by crossing to OVA-specific DO11.10 TCR-transgenic mice. Lungs from the double-transgenic mice developed lymphocytic infiltrates and modest mucus cell hyperplasia. Infiltrating cells were unaffected by the absence of either Rag-1 or Stat6, although the latter deficiency led to the disappearance of mucus. In the lung of double-transgenic mice, a large number of Ag-specific CD4 T cells expressed CD25 and functioned as regulatory T cells. The CD25(+) CD4 T cells suppressed proliferation of CD25(-) CD4 T cells in vitro and inhibited type 2 immune responses induced by aerosolized Ags in vivo. Despite their ability to suppress allergic type 2 immunity in the airways, however, CD25(+) CD4 regulatory T cells had no effect on the development of bronchial hyperreactivity.     

Cutting edge: effector memory CD8+ T cells in the lung airways retain the potential to mediate recall responses

Previous studies have shown that long-lived memory CD8(+) T cells persist in the lung airways following the resolution of a murine Sendai virus infection. These cells are CD11a(low), noncytolytic, and do not proliferate in the lung airways raising the possibility that they are "end stage" or terminally differentiated memory cells. In this current report, we investigated the functional characteristics of these cells by analyzing their capacity to respond to secondary viral infection outside of the lung environment. We show that, after transfer into the bloodstream, CD11a(low) memory T cells from the lung airways can return to the secondary lymphoid tissue and respond to a secondary viral challenge. Furthermore, these cells re-express CD11a, which may contribute to their migratory and proliferative capacity. These data demonstrate that lung airway memory CD8(+) T cells are not terminally differentiated cells and retain the capacity to mediate recall responses to infection.     

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.     

CD4+ and CD8+ T cells exhibit differential requirements for CCR7-mediated antigen transport during influenza infection

Upon encounter of viral Ags in an inflammatory environment, dendritic cells up-regulate costimulatory molecules and the chemokine receptor CCR7, with the latter being pivotal for their migration to the lymph node. By utilizing mice deficient in CCR7, we have examined the requirement of dendritic cell-mediated Ag transport from the lung to the draining lymph node for the induction of anti-influenza immune responses in vivo. We found that CCR7-mediated migration of dendritic cells was more crucial for CD8(+) T cell than CD4(+) T cell responses. While no specific CD8(+) T cell response could be detected in the airways or lymphoid tissues during the primary infection, prolonged infection in CCR7-deficient mice did result in a sustained inflammatory chemokine profile, which led to nonspecific CD8(+) T cell recruitment to the airways. The recruitment of influenza-specific CD4(+) T cells to the airways was also below levels of detection in the absence of CCR7 signaling, although a small influenza-specific CD4(+) T cell population was detectable in the draining lymph node, which was sufficient for the generation of class-switched anti-influenza Abs and a normal CD4(+) T cell memory population. Overall, our data show that CCR7-mediated active Ag transport is differentially required for CD4(+) and CD8(+) T cell expansion during influenza infection.     

Contribution of antigen-primed CD8+ T cells to the development of airway hyperresponsiveness and inflammation is associated with IL-13

The role of Th2/CD4 T cells, which secrete IL-4, IL-5, and IL-13, in allergic disease is well established; however, the role of CD8(+) T cells (allergen-induced airway hyperresponsiveness (AHR) and inflammation) is less clear. This study was conducted to define the role of Ag-primed CD8(+) T cells in the development of these allergen-induced responses. CD8-deficient (CD8(-/-)) mice and wild-type mice were sensitized to OVA by i.p. injection and then challenged with OVA via the airways. Compared with wild-type mice, CD8(-/-) mice developed significantly lower airway responsiveness to inhaled methacholine and lung eosinophilia, and exhibited decreased IL-13 production both in vivo, in the bronchoalveolar lavage (BAL) fluid, and in vitro, following Ag stimulation of peribronchial lymph node (PBLN) cells in culture. Reconstitution of sensitized and challenged CD8(-/-) mice with allergen-sensitized CD8(+) T cells fully restored the development of AHR, BAL eosinophilia, and IL-13 levels in BAL and in culture supernatants from PBLN cells. In contrast, transfer of naive CD8(+) T cells or allergen-sensitized CD8(+) T cells from IL-13-deficient donor mice failed to do so. Intracellular cytokine staining of lung as well as PBLN T cells revealed that CD8(+) T cells were a source of IL-13. These data suggest that Ag-primed CD8(+) T cells are required for the full development of AHR and airway inflammation, which appears to be associated with IL-13 production from these primed T cells.     

Activation, differentiation, and migration of naive virus-specific CD8+ T cells during pulmonary influenza virus infection

The low precursor frequency of individual virus-specific CD8(+) T cells in a naive host makes the early events of CD8(+) T cell activation, proliferation, and differentiation in response to viral infection a challenge to identify. We have therefore examined the response of naive CD8(+) T cells to pulmonary influenza virus infection with a murine adoptive transfer model using hemagglutinin-specific TCR transgenic CD8(+) T cells. Initial activation of CD8(+) T cells occurs during the first 3 days postinfection exclusively within the draining lymph nodes. Acquisition of CTL effector functions, including effector cytokine and granule-associated protease expression, occurs in the draining lymph nodes and differentially correlates with cell division. Division of activated CD8(+) T cells within the draining lymph nodes occurs in an asynchronous manner between days 3 and 4 postinfection. Despite the presence of Ag for several days within the draining lymph nodes, dividing T cells do not appear to maintain contact with residual Ag. After multiple cell divisions, CD8(+) T cells exit the draining lymph nodes and migrate to the infected lung. Activated CD8(+) T cells also disseminate throughout lymphoid tissue including the spleen and distal lymph nodes following their emigration from draining lymph nodes. These results demonstrate an important role for draining lymph nodes in orchestrating T cell responses during a local infection of a discrete organ to generate effector CD8(+) T cells capable of responding to infection and seeding peripheral lymphoid tissues.     

TNF receptor-associated factor 1 expressed in resident lung cells is required for the development of allergic lung inflammation

TNF is a major therapeutic target in a range of chronic inflammatory disorders, including asthma. TNFR-associated factor (TRAF)1 is an intracellular adaptor molecule important for signaling by TNFR. In this study, we investigated the role of TRAF1 in an adoptive transfer model of allergic lung inflammation. Mice deficient in TRAF1 (TRAF1(-/-)) and wild-type (WT) control animals were adoptively transferred with WT OVA-immune CD4(+) T cells, exposed to an aerosol of LPS-free OVA, and analyzed for the development of allergic lung inflammation. In contrast to WT mice, TRAF1(-/-) recipients failed to display goblet cell hyperplasia, eosinophilic inflammation, and airway hyperresponsiveness in this model of asthma. Neither T cell recruitment nor expression of the proinflammatory cytokines IL-4, IL-5, IL-13, or TNF occurred in the lungs of TRAF1(-/-) mice. Although purified myeloid TRAF1(-/-) dendritic cells (DCs) exhibited normal Ag-presenting function and transmigratory capacity in vitro and were able to induce OVA-specific immune responses in the lung draining lymph nodes (LNs) following adoptive transfer in vivo, CD11c(+)CD11b(+) DCs from airways of TRAF1(-/-) recipients were not activated, and purified draining LN cells did not proliferate in vitro. Moreover, transfer of WT or TRAF1(-/-) DCs failed to restore T cell recruitment and DC activation in the airways of TRAF1(-/-) mice, suggesting that the expression of TRAF1 in resident lung cells is required for the development of asthma. Finally, we demonstrate that T cell-transfused TRAF1(-/-) recipient mice demonstrated impaired up-regulation of ICAM-1 expression on lung cells in response to OVA exposure.