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.     

Airway inflammation and IgE production induced by dust mite allergen-specific memory/effector Th2 cell line can be effectively attenuated by IL-35

CD4(+) memory/effector T cells play a central role in orchestrating the rapid and robust immune responses upon re-encounter with specific Ags. However, the immunologic mechanism(s) underlying these responses are still not fully understood. To investigate this, we generated an allergen (major house dust mite allergen, Blo t 5)-specific murine Th2 cell line that secreted IL-4, IL-5, IL-10, and IL-13, but not IL-9 or TNF-α, upon activation by the cognate Ag. These cells also exhibited CD44(high)CD62L(-) and CD127(+) (IL-7Rα(+)) phenotypes, which are characteristics of memory/effector T cells. Experiments involving adoptive transfer of this Th2 cell line in mice, followed by three intranasal challenges with Blo t 5, induced a dexamethasone-sensitive eosinophilic airway inflammation. This was accompanied by elevation of Th2 cytokines and CC- and CXC-motif chemokines, as well as recruitment of lymphocytes and polymorphic mononuclear cells into the lungs. Moreover, Blo t 5-specific IgE was detected 4 d after the last intranasal challenge, whereas elevation of Blo t 5-specific IgG1 was found at week two. Finally, pulmonary delivery of the pVAX-IL-35 DNA construct effectively downregulated Blo t 5-specific allergic airway inflammation, and i.m. injection of pVAX-IL-35 led to long-lasting suppression of circulating Blo t 5-specific and total IgE. This model provides a robust research tool to elucidate the immunopathogenic role of memory/effector Th2 cells in allergic airway inflammation. Our results suggested that IL-35 could be a potential therapeutic target for allergic asthma through its attenuating effects on allergen-specific CD4(+) memory/effector Th2 cell-mediated airway inflammation.     

Differential regulatory function of resting and preactivated allergen-specific CD4+ CD25+ regulatory T cells in Th2-type airway inflammation

Although CD4(+)CD25(+) regulatory T (Treg) cells are known to suppress Th1 cell-mediated immune responses, their effect on Th2-type immune responses remains unclear. In this study we examined the role of Treg cells in Th2-type airway inflammation in mice. Depletion and reconstitution experiments demonstrated that the Treg cells of naive mice effectively suppressed the initiation and development of Th2-driven airway inflammation. Despite effective suppression of Th2-type airway inflammation in naive mice, adoptively transferred, allergen-specific Treg cells were unable to suppress airway inflammation in allergen-presensitized mice. Preactivated allergen-specific Treg cells, however, could suppress airway inflammation even in allergen-presensitized mice by accumulating in the lung, where they reduced the accumulation and proliferation of Th2 cells. Upon activation, allergen-specific Treg cells up-regulated CCR4, exhibited enhanced chemotactic responses to CCR4 ligands, and suppressed the proliferation of and cytokine production by polarized Th2 cells. Collectively, these results demonstrated that Treg cells are capable of suppressing Th2-driven airway inflammation even in allergen-presensitized mice in a manner dependent on their efficient migration into the inflammatory site and their regulation of Th2 cell activation and proliferation.     

Priming of CTLs by lymphocytic choriomeningitis virus depends on dendritic cells

Appropriate activation of naive CD8(+) T cells depends on the coordinated interaction of these cells with professional APC that present antigenic peptides in the context of MHC class I molecules. It is accepted that dendritic cells (DC) are efficient in activating naive T cells and are unique in their capacity to prime CD8(+) T cell responses against exogenous cell-associated Ags. Nevertheless, it is unclear whether epitopes, derived from endogenously synthesized proteins and presented by MHC class I molecules on the surface of other APC including B cells and macrophages, can activate naive CD8(+) T cells in vivo. By infecting transgenic CD11c-DTR/GFP mice that allow conditional depletion of DC with lymphocytic choriomeningitis virus (LCMV), which infects all types of APC and elicits a vigorous CTL response, we unambiguously show that priming of LCMV-specific CD8(+) T cells is crucially dependent on DC, despite ample presence of LCMV-infected macrophages and B cells in secondary lymphoid organs.     

Attenuation of allergen-induced responses in CCR6-/- mice is dependent upon altered pulmonary T lymphocyte activation

We have established a defect in CCR6-/- mice in response to a cockroach allergen airway challenge characterized by decreased IL-5 production, reduced CD4+ T and B cells as well as decreased eosinophil accumulation. To determine the nature of the defect in CCR6-/- mice T lymphocyte populations from allergen-sensitized wild-type mice were transferred into sensitized CCR6-/- mice. The reconstituted response was characterized by an increase in IL-5 levels, eosinophil accumulation, and serum IgE levels in recipient CCR6-/- mice. Analysis of lymphocytes from draining lymph nodes of CCR6+/+ and CCR6-/- sensitized or challenged mice demonstrated a significant decrease in IL-5 and IL-13 production in CCR6-/- mice. In contrast, the systemic response in allergen-rechallenged spleen cells demonstrated no significant alteration in allergen-induced cytokine production. Transfer of isolated splenic T lymphocytes from sensitized CCR6+/+ mice induced airway hyperresponsiveness in wild-type but not CCR6-/- naive mice, suggesting that T cells alone were not sufficient to induce airway hyperresponsiveness in CCR6-/- mice. Additional analysis demonstrated decreased CD11c+, CD11b+ and CD11c, and B220 subsets of dendritic cells in the lungs of CCR6-/- mice after allergen challenge. Using in vitro cell mixing studies with isolated pulmonary CD4+ T cells and CD11c+ cells from CCR6+/+ or CCR6-/- mice, we demonstrate alterations in both CCR6-/- T cells and CCR6-/- pulmonary APCs to elicit IL-5 responses. Altogether, the defect in CCR6-/- mice appears to be primarily due to an alteration in T cell activation, but also appears to include local pulmonary APC defects.     

Tissue localization and frequency of antigen-specific effector CD4 T cells determines the development of allergic airway inflammation

Previous activation of effector Th2 cells is central to the development of allergic inflammatory responses. We have observed that priming of allergen-specific Th2 cells in C57BL/6 or B10.A mice with allergen delivered via the i.p. or s.c. routes results in very different outcomes following subsequent airway exposure to the same allergen. Systemic allergen immunization (via the i.p. route) resulted in the formation of a lung-resident population of allergen-specific T cells, and mice developed severe allergic airway inflammation in response to inhaled allergen. The localization of cells to the lung did not require the presence of antigen at this site, but reflected a large pool of circulating activated allergen-specific T cells. In contrast, localized immunization (via the s.c. route) resulted in a small T-cell response restricted to the draining lymph node, and mice were not responsive to inhaled allergen. These data indicate that prior sensitization to an allergen alone was not sufficient for the induction of allergic inflammation; rather, responsiveness was largely determined by precursor frequency and tissue localization of the allergen-specific effector Th2 cells.     

A CD91-positive subset of CD11c+ blood dendritic cells: characterization of the APC that functions to enhance adaptive immune responses against CD91-targeted antigens

Dendritic cells (DC) and other APCs rely on a number of specialized receptors to facilitate the uptake and intracellular accumulation of Ags. In this capacity, APCs use receptor-mediated endocytosis to enhance Ag presentation and the stimulation of Ag-specific T cells. Studies have demonstrated that the targeted delivery of Ags in vivo to CD91/the low-density lipoprotein receptor-related protein (CD91/LRP) induces enhanced activation of the adaptive immune system. However, the APC that mediates these augmented, Ag-specific responses remains to be characterized. In this study, we show that a subset of CD11c(+) lineage-negative (lin(-)) DC expresses the scavenger receptor CD91/LRP and that these rare APC are primarily responsible for the T cell activation that occurs following CD91/LRP-mediated Ag uptake in whole blood. The targeting of Ags to CD91/LRP results in enhanced receptor-mediated uptake within both lin(-) DCs and monocytes, and this uptake results in markedly increased T cell activation. Finally, purified cellular populations were used to demonstrate that CD11c(+) lin(-) DC, but not monocytes, are capable of stimulating T cell activation following CD91/LRP-mediated Ag uptake. Therefore, CD11c(+) lin(-) DC use CD91/LRP to facilitate the uptake and subsequent presentation of an array of Ags complexed within the CD91/LRP ligand, the activated form of alpha2-macroglobulin (alpha2M*).     

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: in vitro-generated tolerogenic APC induce CD8+ T regulatory cells that can suppress ongoing experimental autoimmune encephalomyelitis

APC exposed to TGFbeta2 and Ag (tolerogenic APC) promote peripheral Ag-specific tolerance via the induction of CD8(+) T regulatory cells capable of suppressing Th1 and Th2 immunity. We postulated that tolerogenic APC might reinstate tolerance toward self-neuronal Ags and ameliorate ongoing experimental autoimmune encephalomyelitis (EAE). Seven days after immunization with myelin basic protein (MBP), mice received MBP-specific tolerogenic APC, and EAE was evaluated clinically. To test for the presence and the phenotype of T regulatory cells, CD4 and/or CD8 T cells from tolerogenic APC-treated mice were transferred to naive mice before their immunization with MBP. The MBP-specific tolerogenic APC decreased both the severity and incidence of ongoing EAE. Tolerance to self-neuronal Ags was induced in naive recipient mice via adoptive transfer of CD8(+), but not CD4(+) T cells. Rational use of in vitro-generated tolerogenic APC may lead to novel therapy for autoimmune disease.     

Functional specializations of intestinal dendritic cell and macrophage subsets that control Th17 and regulatory T cell responses are dependent on the T cell/APC ratio, source of mouse strain, and regional localization

Although several subsets of intestinal APCs have been described, there has been no systematic evaluation of their phenotypes, functions, and regional localization to date. In this article, we used 10-color flow cytometry to define the major APC subsets in the small and large intestine lamina propria. Lamina propria APCs could be subdivided into CD11c(+)CD11b(-), CD11c(+)CD11b(+), and CD11c(dull)CD11b(+) subsets. CD11c(+)CD11b(-) cells were largely CD103(+)F4/80(-) dendritic cells (DCs), whereas the CD11c(+)CD11b(+) subset comprised CD11c(+)CD11b(+)CD103(+)F4/80(-) DCs and CD11c(+)CD11b(+)CD103(-)F4/80(+) macrophage-like cells. The majority of CD11c(dull)CD11b(+) cells were CD103(-)F4/80(+) macrophages. Although macrophages were more efficient at inducing Foxp3(+) regulatory T (T(reg)) cells than DCs, at higher T cell/APC ratios, all of the DC subsets efficiently induced Foxp3(+) T(reg) cells. In contrast, only CD11c(+)CD11b(+)CD103(+) DCs efficiently induced Th17 cells. Consistent with this, the regional distribution of CD11c(+)CD11b(+)CD103(+) DCs correlated with that of Th17 cells, with duodenum > jejunum > ileum > colon. Conversely, CD11c(+)CD11b(-)CD103(+) DCs, macrophages, and Foxp3(+) T(reg) cells were most abundant in the colon and scarce in the duodenum. Importantly, however, the ability of DC and macrophage subsets to induce Foxp3(+) T(reg) cells versus Th17 cells was strikingly dependent on the source of the mouse strain. Thus, DCs from C57BL/6 mice from Charles River Laboratories (that have segmented filamentous bacteria, which induce robust levels of Th17 cells in situ) were more efficient at inducing Th17 cells and less efficient at inducing Foxp3(+) T(reg) cells than DCs from B6 mice from The Jackson Laboratory. Thus, the functional specializations of APC subsets in the intestine are dependent on the T cell/APC ratio, regional localization, and source of the mouse strain.     

Transfer of the enhancing effect of respiratory syncytial virus infection on subsequent allergic airway sensitization by T lymphocytes.

In mice, respiratory syncytial virus (RSV) infection enhances allergic airway sensitization, resulting in lung eosinophilia and in airway hyperresponsiveness (AHR). The mechanisms by which RSV contributes to development of asthma and its effects on allergic airway sensitization in mice are not known. We tested whether these consequences of RSV infection can be adoptively transferred by T cells and whether depletion of T cell subsets prevents the effects of RSV infection on subsequent airway sensitization. Mononuclear cells, T lymphocytes, or CD4 or CD8 T cells from peribronchial lymph nodes (PBLN) of RSV-infected mice were transferred into naive BALB/c mice which were then exposed to OVA via the airways. Additionally, RSV-infected mice were depleted of CD4 or CD8 T cells following acute RSV infection but prior to airway sensitization. Following sensitization, airway responsiveness to inhaled methacholine, numbers of lung eosinophils, and levels of IFN-gamma, IL-4, and IL-5 in PBLN cell cultures were monitored. Transfer of T cells from RSV-infected mice resulted in increased eosinophil influx into the lungs, increased IL-5 production, and development of AHR following airway sensitization to allergen. Transfer of CD8 but not CD4 T cells from the PBLN of RSV-infected mice also resulted in AHR following 10 days of OVA exposure. Further, depletion of CD8 T cells prevented these consequences of RSV infection while CD4 T cell depletion reduced them. We conclude that T cells, in particular CD8 T cells, are critical in mediating RSV-induced development of lung eosinophilia and AHR following allergic airway sensitization.     

Multiple chemokine receptors, including CCR6 and CXCR3, regulate antigen-induced T cell homing to the human asthmatic airway

Human allergic asthma is a chronic inflammatory disease of the airways thought to be driven by allergen-specific Th2 cells, which are recruited into the lung in response to inhaled allergen. To identify chemoattractant receptors that control this homing pattern, we used endobronchial segmental allergen challenge in human atopic asthmatics to define the pattern of chemoattractant receptor expression on recruited T cells as well as the numbers of recruited CD1d-restricted NKT cells and levels of chemokines in the bronchoalveolar (BAL) fluid. CD1d-restricted NKT cells comprised only a small minority of BAL T cells before or after Ag challenge. BAL T cells were enriched in their expression of specific chemoattractant receptors compared with peripheral blood T cells prechallenge, including CCR5, CCR6, CXCR3, CXCR4, and BLT1. Surprisingly, following segmental allergen challenge, no chemoattractant receptor was specifically increased. However, CCR6 and CXCR3, which were expressed on virtually all CD4(+) BAL T cells prechallenge, were markedly decreased on all recruited BAL T cells following Ag challenge, suggesting that these receptors were internalized following encounter with ligand in the airway. Our data therefore suggests a role for CCR6 and CXCR3, in conjunction with other chemoattractant receptors, in the recruitment of inflammatory T cells into the BAL during the allergic asthmatic response.     

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.     

IL-10-producing B220+CD11c- APC in mouse spleen

APC acting at the early stages of an immune response can shape the nature of that response. Such APC will include dendritic cells (DCs) but may also include populations of B cells such as marginal zone B cells in the spleen. In this study, we analyze APC populations in mouse spleen and compare the phenotype and function of B220(+)CD11c(-) populations with those of CD11c(+) spleen DC subsets. Low-density B220(+) cells had morphology similar to DCs and, like DCs, they could stimulate naive T cells, and expressed high levels of MHC and costimulatory molecules. However, the majority of the B220(+) cells appeared to be of B cell lineage as demonstrated by coexpression of CD19 and surface Ig, and by their absence from RAG-2(-/-) mice. The phenotype of these DC-like B cells was consistent with that of B cells in the marginal zone of the spleen. On bacterial stimulation, they preferentially produced IL-10 in contrast to the DCs, which produced IL-12. Conventional B cells did not produce IL-10. The DC-like B cells could be induced to express low levels of the DC marker CD11c with maturational stimuli. A minority of the B220(+)CD11c(-) low-density cells did not express CD19 and surface Ig and may be a DC subset; this population also produced IL-10 on bacterial stimulation. B220(+) APC in mouse spleen that stimulate naive T cells and preferentially produce IL-10 may be involved in activating regulatory immune responses.     

Allergen-specific CTL require perforin expression to suppress allergic airway inflammation

Allergen-specific CTL have a protective effect on allergic airway inflammation, a function thought to be mediated by cytokines, especially IFN-γ. However, the contribution of cytotoxic function to this protective effect has not been investigated. We examined the contribution of cytotoxic function to the therapeutic effect of allergen-specific CTL in allergic airway inflammation. We used a murine model of allergic airway inflammation in which mice were sensitized to OVA and then challenged with the same Ag via the intranasal route. CTL were elicited in these mice by immunization with dendritic cells (DC) or by adoptive transfer of in vitro-activated CD8(+) T cells. Hallmark features of allergic asthma, such as infiltration of eosinophils in the bronchoalveolar lavage fluid and mucus production, were assessed. Suppression of allergic airway inflammation by allergen-specific CTL was critically dependent on the expression of perforin, a key component of the cytotoxic machinery. Both perforin-sufficient and perforin-deficient allergen-specific CTL were recovered from the lungs of allergen-sensitized mice and upregulated CD69 expression and secreted the cytokines IFN-γ and TNF-α upon intranasal allergen challenge. However, only perforin-sufficient CTL inhibited eosinophil infiltration in the airway, mucus production, and cytokine accumulation in the bronchoalveolar lavage fluid. Treatment with allergen-specific CTL, but not their perforin-deficient counterparts, was also associated with a decrease in the number of DC in the mediastinal lymph node. Our data suggest that the cytotoxic function of allergen-specific CD8(+) T cells is critical to their ability to moderate allergic airway inflammation.     

TGF-beta-producing CD4+ mediastinal lymph node cells obtained from mice tracheally tolerized to ovalbumin (OVA) suppress both Th1- and Th2-induced cutaneous inflammatory responses to OVA by different mechanisms

Advances in the treatment of allergic disorders require elucidation of the autoregulatory immune systems induced in averting detrimental inflammatory responses against invading foreign Ags. We previously reported that excessive Ags intruding through the airway mucosa induce a subset of regulatory CD4+ T cells secreting TGF-beta in the regional mediastinal lymph nodes (MLNs), which inhibits Th2 cells and subsequent eosinophilic inflammation in the trachea. In the present experiments we examined whether and in what mechanisms TGF-beta-secreting CD4+ T cells in the MLNs regulate Th cell-mediated skin inflammation using a previously established murine model. Th1 or Th2 cells injected s.c. into ear lobes of naive mice induced swelling, whereas the concomitant local injection of MLN cells suppressed the inflammation. The suppressor activities of MLN cells were markedly neutralized by anti-TGF-beta mAb and were mimicked by rTGF-beta. The MLN cell- and rTGF-beta-induced inhibition was reversed by anti-IL-10 mAb significantly in Th1-induced inflammation and only partially in Th2-induced inflammation. rIL-10 reduced Th-induced ear swelling, although higher doses of rIL-10 were required in Th2-induced one. Thus, allergen-specific TGF-beta-producing CD4+ T cells induced in the respiratory tract controlled cutaneous inflammatory responses by Th1 or Th2 cells either directly by TGF-beta or indirectly through IL-10 induction. From a clinical standpoint, these observations might explain the mechanism of spontaneous regression in some patients with atopic dermatitis, which exhibits both Th1- and Th2-mediated skin inflammation in response to airborne protein Ags.     

Gastrointestinal dendritic cells promote Th2 skewing via OX40L

Mice can be sensitized to food proteins by oral administration with the adjuvant cholera toxin (CT), such that they undergo anaphylaxis when rechallenged with the sensitizing allergen. In contrast, feeding of Ags alone leads to oral tolerance. Our aim was to define the mechanisms by which gastrointestinal dendritic cells (DCs) participate in the deviation of tolerance to allergic sensitization in the gut in response to CT. BALB/c mice were fed with CT or PBS. The impact of CT on DC subsets in the mesenteric lymph node (MLN) was assessed by flow cytometry. Ag presentation assays were performed with DCs isolated from the MLN of PBS- or CT-fed mice, using OVA-specific CD4(+) T cells as responder cells. Gene expression in MLN DCs was determined by real-time PCR, and neutralizing Abs were used to test the function of OX40 ligand (OX40L) in Th2 skewing. Oral administration of CT induced an increase in the total CD11c(+) population in the MLN. CT induced a selective increase in migration of the CD11c(+)CD11b(-)CD8alpha(-) DC subset and the maturation of all DC subsets. Maturation of DCs in vivo enhanced T cell proliferation and cytokine secretion. Oral CT induced up-regulation of Jagged-2 and OX40L by MLN DCs. Neutralizing anti-OX40L Abs completely abrogated the CT-induced Th2 cytokine response. We show that oral CT induces selective DC migration, maturation, and T cell priming activity in the MLN. Th2 skewing is mediated by OX40L, and we speculate that this molecule may be an important inducer of allergic sensitization to food allergens.     

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.     

Both Memory and CD45RA+/CD62L+ Naive CD4+ T Cells Are Infected in Human Immunodeficiency Virus Type 1-Infected Individuals

Cellular activation is critical for the propagation of human immunodeficiency virus type 1 (HIV-1) infection. It has been suggested that truly naive CD4(+) T cells are resistant to productive HIV-1 infection because of their constitutive resting state. Memory and naive CD4(+) T-cell subsets from 11 HIV-1-infected individuals were isolated ex vivo by a combination of magnetic bead depletion and fluorescence-activated cell sorting techniques with stringent criteria of combined expression of CD45RA and CD62L to identify naive CD4(+) T-cell subsets. In all patients HIV-1 provirus could be detected within naive CD45RA+/CD62L+ CD4(+) T cells; in addition, replication-competent HIV-1 was isolated from these cells upon CD4(+) T-cell stimulation in tissue cultures. Memory CD4(+) T cells had a median of fourfold more replication-competent virus and a median of sixfold more provirus than naive CD4(+) T cells. Overall, there was a median of 16-fold more integrated provirus identified in memory CD4(+) T cells than in naive CD4(+) T cells within a given patient. Interestingly, there was a trend toward equalization of viral loads in memory and naive CD4(+) T-cell subsets in those patients who harbored CXCR4-using (syncytium-inducing) viruses. Within any given patient, there was no selective usage of a particular coreceptor by virus isolated from memory versus naive CD4(+) T cells. Our findings suggest that naive CD4(+) T cells may be a significant viral reservoir for HIV, particularly in those patients harboring CXCR4-using viruses.