NOD2 Signaling Circuitry during Allergen Sensitization Does Not Worsen Experimental Neutrophilic Asthma but Promotes a Th2/Th17 Profile in Asthma Patients but Not Healthy Subjects.

Nucleotide-binding oligomerization domain 2 (NOD2) recognizes pathogens associated with the development of asthma. Moreover, NOD2 adjuvants are used in vaccine design to boost immune responses. Muramyl di-peptide (MDP) is a NOD2 ligand, which is able to promote Th2/Th17 responses. Furthermore, polymorphisms of the NOD2 receptor are associated with allergy and asthma development. This study aimed to evaluate if MDP given as an adjuvant during allergen sensitization may worsen the development of Th2/Th17 responses. We used a mouse model of Th2/Th17-type allergic neutrophil airway inflammation (AAI) to dog allergen, with in vitro polarization of human naive T cells by dendritic cells (DC) from healthy and dog-allergic asthma subjects. In the mouse model, intranasal co-administration of MDP did not modify the AAI parameters, including Th2/Th17-type lung inflammation. In humans, MDP co-stimulation of allergen-primed DC did not change the polarization profile of T cells in healthy subjects but elicited a Th2/Th17 profile in asthma subjects, as compared with MDP alone. These results support the idea that NOD2 may not be involved in the infection-related development of asthma and that, while care has to be taken in asthma patients, NOD2 adjuvants might be used in non-sensitized individuals.

Natural Killer Cells from Allergic Donors Are Defective in Their Response to CCL18 Chemokine.

Natural killer (NK) cells were originally described as cytolytic effector cells, but since then have been recognized to possess regulatory functions on immune responses. Chemokines locate NK cells throughout the body in homeostatic and pathological conditions. They may also directly stimulate immune cells. CCL18 is a constitutive and inducible chemokine involved in allergic diseases. The aim of this study was to evaluate CCL18's effect on NK cells from allergic and nonallergic donors in terms of both chemotactic and immune effects. Results showed that CCL18 was able to induce migration of NK cells from nonallergic donors in a G-protein-dependent manner, suggesting the involvement of a classical chemokine receptor from the family of seven-transmembrane domain G-protein-coupled receptors. In contrast, NK cells from allergic patients were unresponsive. Similarly, CCL18 was able to induce NK cell cytotoxicity only in nonallergic subjects. Purified NK cells did not express CCR8, one of the receptors described to be involved in CCL18 functions. Finally, the defect in CCL18 response by NK cells from allergic patients was unrelated to a defect in CCL18 binding to NK cells. Overall, our results suggest that some NK cell functions may be defective in allergic diseases.

NOD1 sensing of house dust mite-derived microbiota promotes allergic experimental asthma.

BACKGROUND: Asthma severity has been linked to exposure to gram-negative bacteria from the environment that are recognized by NOD1 receptor and are present in house dust mite (HDM) extracts. NOD1 polymorphism has been associated with asthma. OBJECTIVE: We sought to evaluate whether either host or HDM-derived microbiota may contribute to NOD1-dependent disease severity. METHODS: A model of HDM-induced experimental asthma was used and the effect of NOD1 deficiency was evaluated. Contribution of host microbiota was evaluated by fecal transplantation. Contribution of HDM-derived microbiota was assessed by 16S ribosomal RNA sequencing, mass spectrometry analysis, and peptidoglycan depletion of the extracts. RESULTS: In this model, loss of the bacterial sensor NOD1 and its adaptor RIPK2 improved asthma features. Such inhibitory effect was not related to dysbiosis caused by NOD1 deficiency, as shown by fecal transplantation of Nod1-deficient microbiota to wild-type germ-free mice. The 16S ribosomal RNA gene sequencing and mass spectrometry analysis of HDM allergen, revealed the presence of some muropeptides from gram-negative bacteria that belong to the Bartonellaceae family. While such HDM-associated muropeptides were found to activate NOD1 signaling in epithelial cells, peptidoglycan-depleted HDM had a decreased ability to instigate asthma in vivo. CONCLUSIONS: These data show that NOD1-dependent sensing of HDM-associated gram-negative bacteria aggravates the severity of experimental asthma, suggesting that inhibiting the NOD1 signaling pathway may be a therapeutic approach to treating asthma.

Innate lymphoid cells contribute to allergic airway disease exacerbation by obesity.

BACKGROUND: Epidemiologic and clinical observations identify obesity as an important risk factor for asthma exacerbation, but the underlying mechanisms remain poorly understood. Type 2 innate lymphoid cells (ILC2s) and type 3 innate lymphoid cells (ILC3s) have been implicated, respectively, in asthma and adipose tissue homeostasis and in obesity-associated airway hyperresponsiveness (AHR). OBJECTIVE: We sought to determine the potential involvement of innate lymphoid cells (ILCs) in allergic airway disease exacerbation caused by high-fat diet (HFD)-induced obesity. METHODS: Obesity was induced by means of HFD feeding, and allergic airway inflammation was subsequently induced by means of intranasal administration of house dust mite (HDM) extract. AHR, lung and visceral adipose tissue inflammation, humoral response, cytokines, and innate and adaptive lymphoid populations were analyzed in the presence or absence of ILCs. RESULTS: HFD feeding exacerbated allergic airway disease features, including humoral response, airway and tissue eosinophilia, AHR, and TH2 and TH17 pulmonary profiles. Notably, nonsensitized obese mice already exhibited increased lung ILC counts and tissue eosinophil infiltration compared with values in lean mice in the absence of AHR. The numbers of total and cytokine-expressing lung ILC2s and ILC3s further increased in HDM-challenged obese mice compared with those in HDM-challenged lean mice, and this was accompanied by high IL-33 and IL-1ß levels and decreased ILC markers in visceral adipose tissue. Furthermore, depletion of ILCs with an anti-CD90 antibody, followed by T-cell reconstitution, led to a profound decrease in allergic airway inflammatory features in obese mice, including TH2 and TH17 infiltration. CONCLUSION: These results indicate that HFD-induced obesity might exacerbate allergic airway inflammation through mechanisms involving ILC2s and ILC3s.

Protein Kinase C-Mediated Phosphorylation of BCL11B at Serine 2 Negatively Regulates Its Interaction with NuRD Complexes during CD4+ T-Cell Activation.

The transcription factor BCL11B/CTIP2 is a major regulatory protein implicated in various aspects of development, function and survival of T cells. Mitogen-activated protein kinase (MAPK)-mediated phosphorylation and SUMOylation modulate BCL11B transcriptional activity, switching it from a repressor in naive murine thymocytes to a transcriptional activator in activated thymocytes. Here, we show that BCL11B interacts via its conserved N-terminal MSRRKQ motif with endogenous MTA1 and MTA3 proteins to recruit various NuRD complexes. Furthermore, we demonstrate that protein kinase C (PKC)-mediated phosphorylation of BCL11B Ser2 does not significantly impact BCL11B SUMOylation but negatively regulates NuRD recruitment by dampening the interaction with MTA1 or MTA3 (MTA1/3) and RbAp46 proteins. We detected increased phosphorylation of BCL11B Ser2 upon in vivo activation of transformed and primary human CD4(+) T cells. We show that following activation of CD4(+) T cells, BCL11B still binds to IL-2 and Id2 promoters but activates their transcription by recruiting P300 instead of MTA1. Prolonged stimulation results in the direct transcriptional repression of BCL11B by KLF4. Our results unveil Ser2 phosphorylation as a new BCL11B posttranslational modification linking PKC signaling pathway to T-cell receptor (TCR) activation and define a simple model for the functional switch of BCL11B from a transcriptional repressor to an activator during TCR activation of human CD4(+) T cells.

Apical Organelle Secretion by Toxoplasma Controls Innate and Adaptive Immunity and Mediates Long-Term Protection.

Apicomplexan parasites have unique apical rhoptry and microneme secretory organelles that are crucial for host infection, although their role in protection against Toxoplasma gondii infection is not thoroughly understood. Here, we report a novel function of the endolysosomal T. gondii sortilin-like receptor (TgSORTLR), which mediates trafficking to functional apical organelles and their subsequent secretion of virulence factors that are critical to the induction of sterile immunity against parasite reinfection. We further demonstrate that the T. gondii armadillo repeats-only protein (TgARO) mutant, which is deficient only in apical secretion of rhoptries, is also critical in mounting protective immunity. The lack of TgSORTLR and TgARO proteins completely inhibited T-helper 1-dependent adaptive immunity and compromised the function of natural killer T-cell-mediated innate immunity. Our findings reveal an essential role for apical secretion in promoting sterile protection against T. gondii and provide strong evidence for rhoptry-regulated discharge of antigens as a key effector for inducing protective immunity.

Polycyclic aromatic hydrocarbons reciprocally regulate IL-22 and IL-17 cytokines in peripheral blood mononuclear cells from both healthy and asthmatic subjects.

Pollution, including polycyclic aromatic hydrocarbons (PAH), may contribute to increased prevalence of asthma. PAH can bind to the Aryl hydrocarbon Receptor (AhR), a transcription factor involved in Th17/Th22 type polarization. These cells produce IL17A and IL-22, which allow neutrophil recruitment, airway smooth muscle proliferation and tissue repair and remodeling. Increased IL-17 and IL-22 productions have been associated with asthma. We hypothesized that PAH might affect, through their effects on AhR, IL-17 and IL-22 production in allergic asthmatics. Activated peripheral blood mononuclear cells (PBMCs) from 16 nonallergic nonasthmatic (NA) and 16 intermittent allergic asthmatic (AA) subjects were incubated with PAH, and IL-17 and IL-22 productions were assessed. At baseline, activated PBMCs from AA exhibited an increased IL-17/IL-22 profile compared with NA subjects. Diesel exhaust particle (DEP)-PAH and Benzo[a]Pyrene (B[a]P) stimulation further increased IL-22 but decreased IL-17A production in both groups. The PAH-induced IL-22 levels in asthmatic patients were significantly higher than in healthy subjects. Among PBMCs, PAH-induced IL-22 expression originated principally from single IL-22- but not from IL-17- expressing CD4 T cells. The Th17 transcription factors RORA and RORC were down regulated, whereas AhR target gene CYP1A1 was upregulated. IL-22 induction by DEP-PAH was mainly dependent upon AhR whereas IL-22 induction by B[a]P was dependent upon activation of PI3K and JNK. Altogether, these data suggest that DEP-PAH and B[a]P may contribute to increased IL22 production in both healthy and asthmatic subjects through mechanisms involving both AhR -dependent and -independent pathways.

Kinetic of NO2 uptake by Phleum pratense pollen: chemical and allergenic implications.

Phleum pratense pollen was exposed to NO(2) in a reactor allowing a continuous analysis of NO(2) concentration by FTIR. The uptake coefficient of NO(2) on pollen was calculated postulating a first order kinetic reaction and a value of (1.1 ± 0.1) x 10(-7) was determined. NO(2) uptake was faster when the pollen water content was increased and when the pollen was pre-treated with ozone. The effect of NO(2) exposure on pollen allergic properties was investigated by quantifying Th2- and Th1-associated chemokines in a model of human dendritic cells. Cellular analysis clearly showed that cells exposed to fumigated pollen favored the production of chemokines known to promote Th2-cell responses. Altogether these data demonstrate that NO(2) uptake by pollen directly correlates with increased Th2 response in human cells,and are in favor of the involvement of NO(2) pollution in the increase of allergic diseases.

Natural killer cells induce eosinophil activation and apoptosis.

Eosinophils are potent inflammatory cells with numerous immune functions, including antigen presentation and exacerbation of inflammatory responses through their capacity to release a range of largely preformed cytokines and lipid mediators. Thus, timely regulation of eosinophil activation and apoptosis is crucial to develop beneficial immune response and to avoid tissue damage and induce resolution of inflammation. Natural Killer (NK) cells have been reported to influence innate and adaptive immune responses by multiple mechanisms including cytotoxicity against other immune cells. In this study, we analyzed the effect of the interaction between NK cells and eosinophils. Co-culture experiments revealed that human NK cells could trigger autologous eosinophil activation, as shown by up-regulation of CD69 and down-regulation of CD62L, as well as degranulation, evidenced by increased CD63 surface expression, secretion of eosinophil cationic protein (ECP) and eosinophil derived neurotoxin (EDN). Moreover, NK cells significantly and dose dependently increased eosinophil apoptosis as shown by annexin V and propidium iodide (PI) staining. Direct contact was necessary for eosinophil degranulation and apoptosis. Increased expression of phosphorylated extracellular signal-regulated kinase (ERK) in cocultured eosinophils and inhibition of eosinophil CD63 expression by pharmacologic inhibitors suggest that MAPK and PI3K pathways are involved in NK cell-induced eosinophil degranulation. Finally, we showed that NK cells increased reactive oxygen species (ROS) expression by eosinophils in co-culture and that mitochondrial inhibitors (rotenone and antimycin) partially diminished NK cell-induced eosinophil apoptosis, suggesting the implication of mitochondrial ROS in NK cell-induced eosinophil apoptosis. Pan-caspase inhibitor (ZVAD-FMK) only slightly decreased eosinophil apoptosis in coculture. Altogether, our results suggest that NK cells regulate eosinophil functions by inducing their activation and their apoptosis.

CCL17 production by dendritic cells is required for NOD1-mediated exacerbation of allergic asthma.

RATIONALE: Pattern recognition receptors are attractive targets for vaccine adjuvants, and polymorphisms of the innate receptor NOD1 have been associated with allergic asthma. OBJECTIVES: To elucidate whether NOD1 agonist may favor allergic asthma in humans through activation of dendritic cells, and to evaluate the mechanisms involved using an in vivo model. METHODS: NOD1-primed dendritic cells from allergic and nonallergic donors were characterized in vitro on their phenotype, cytokine secretion, and Th2 polarizing ability. The in vivo relevance was examined in experimental allergic asthma, and the mechanisms were assessed using transfer of NOD1-conditioned dendritic cells from wild-type or CCL17-deficient mice. MEASUREMENTS AND MAIN RESULTS: NOD1 priming of human dendritic cells promoted a Th2 polarization profile that involved the production of CCL17 and CCL22 in nonallergic subjects but only CCL17 in allergic patients, without requiring allergen costimulation. Moreover, NOD1-primed dendritic cells from allergic donors exhibited enhanced maturation that led to abnormal CCL22 and IL-10 secretion compared with nonallergic donors. In mice, systemic NOD1 ligation exacerbated allergen-induced experimental asthma by amplifying CCL17-mediated Th2 responses in the lung. NOD1-mediated sensitization of purified murine dendritic cells enhanced production of CCL17 and CCL22, but not of thymic stromal lymphopoietin and IL-33, in vitro. Consistently, adoptive transfer of NOD1-conditioned dendritic cells exacerbated the Th2 pulmonary response in a CCL17-dependent manner in vivo. CONCLUSIONS: Data from this study unveil a deleterious role of NOD1 in allergic asthma through direct induction of CCL17 by dendritic cells, arguing for a need to address vaccine formulation safety issues related to allergy.

Pulmonary CCL18 recruits human regulatory T cells.

CCL18 is both a constitutively expressed and an inducible chemokine, whose role in the inflammatory reaction is poorly known. The aim of this study was to evaluate whether CCL18 has the capacity to attract human T cells with a regulatory function (regulatory T cells [Treg]). Results from chemotaxis assays performed on different types of Treg showed that CD4(+)CD25(+)CD127(low) cells, but neither T regulatory type 1 clones nor Treg differentiated in vitro with anti-CD3/CD46 mAbs, were recruited by CCL18 in a dose-dependent manner. CCL18-recruited memory CD4(+) T cells were enriched in CD25(high), CD25(+)CD127(low), latency-associated peptide/TGF-ß1, and CCR4-expressing T cells, whereas there was no enrichment in Foxp3(+) cells as compared with controls. Stimulated CCL18-recruited memory T cells produced significantly increased amounts of the regulatory cytokines IL-10 and TGF-ß1, as well as IL-4, but not IFN-γ and IL-17. Cell surface CCL18 binding was found predominantly on IL-10(+) (26.3 ± 5.8%) and on a few latency-associated peptide/TGF-ß1(+) (18.1 ± 1.9%) and IL-4(+) (14.5 ± 2.9%) memory T cells. In an in vivo model of SCID mice grafted with human skin and reconstituted with autologous PBMCs, the intradermal injection of CCL18 led to the cutaneous recruitment of CD4(+), CD25(+), and IL-10(+) cells, but not Foxp3(+) cells. Furthermore, CCL18-recruited memory T cells inhibited the proliferation of CD4(+)CD25(-) effector T cells through an IL-10-dependent mechanism. These data suggest that CCL18 may contribute to maintaining tolerance and/or suppressing deleterious inflammation by attracting memory Tregs into tissues, particularly in the lung, where it is highly and constitutively expressed.

CCL18 differentiates dendritic cells in tolerogenic cells able to prime regulatory T cells in healthy subjects.

The aim of this study was to evaluate the nonchemotactic function of CCL18 on human dendritic cells (DCs). In different protocols of DC differentiation, CCL18 was highly produced, suggesting that it may constitute a mandatory mediator of the differentiation process. Differentiation of monocytes from healthy subjects in the presence of granulocyte-macrophage colony-stimulating factor and CCL18 led to the development of DCs with a semimature phenotype, with intermediate levels of costimulatory and MHC class II molecules, increased CCR7 expression, which induced, in coculture with allogenic naive T cells, an increase in IL-10 production. The generated T cells were able to suppress the proliferation of effector CD4(+)CD25(-) cells, through a cytokine-dependent mechanism, and exhibited characteristics of type 1 T regulatory cells. The generation of tolerogenic DCs by CCL18 was dependent on the production of indoleamine 2,3-dioxigenase through an interleukin-10-mediated mechanism. Surprisingly, when DCs originated from allergic patients, the tolerogenic effect of CCL18 was lost in relation with a decreased binding of CCL18 to its putative receptor. This study is the first to define a chemokine able to generate tolerogenic DCs. However, this function was absent in allergic donors and may participate to the decreased tolerance observed in allergic diseases.

The chemokine CCL18 generates adaptive regulatory T cells from memory CD4+ T cells of healthy but not allergic subjects.

The purpose of this study was to assess the direct effect of CCL18, a chemokine elevated in allergic diseases and induced by Th2 cytokines, on the polarization of human CD4(+) T cells. Purified human T cells from healthy subjects were pretreated or not with CCL18, and evaluated for cytokine production. CCL18-pretreated memory but not naive CD4(+) T cells exhibited an increased production of IL-10 (12.3 ± 2.6 vs. 5.6 ± 0.9 ng/ml for medium) and TGF-ß1 but not IL-4, IFN-γ, and IL-17 compared with control cells. Pretreatment of highly purified CD4(+)CD25(-) memory T cells with CCL18 led to their conversion to CD4(+)CD25(+)Foxp3(+) regulatory T cells able to inhibit the proliferation of CD4(+)CD25(-) effector T cells by both cytokine and cell contact-dependent mechanisms. However, this regulatory effect of CCL18 was lost when T cells originated from allergic subjects in relation with a decreased binding of CCL18 to these cells [0.7 ± 0.3 mean fluorescence intensity (MFI)] as compared to those from healthy subjects (6.0 ± 1.7 MFI). This study is the first to define a chemokine that generates adaptive regulatory T cells from CD4(+)CD25(-) memory T cells. This mechanism appears defective in allergic patients and may underlie the decreased tolerance observed in allergic diseases.

Role of CCL17 in the generation of cutaneous inflammatory reactions in Hu-PBMC-SCID mice grafted with human skin.

CCL17 may be of interest in skin inflammation, because it mainly attracts T cells expressing the cutaneous homing receptor and binds the chemokine receptor CCR4, preferentially expressed on Th-2 cells. We evaluated the in vivo effect of CCL17 injection in a humanized mouse model. (125)I-CCL17 injection into human skin grafted on severe combined immunodeficient (SCID) mice reconstituted with peripheral blood mononuclear cells resulted in a rapid transportation of CCL17 from the skin to the homolateral lymph nodes, followed 3 hours later by a lymph node infiltration of human memory CD4+ cells and dendritic cells. Intradermal injection of CCL17 resulted 24 hours later in a cutaneous recruitment of human memory CD4+ cells, monocytes, and basophils, but also murine eosinophils. In SCID mice reconstituted with polarized Th-1 or Th-2 cells, intradermal injection of CCL17 resulted in the recruitment of IL-4+ Th-2 cells but not of IFN-gamma+ Th-1 cells, whereas CCL17 was able to recruit both subsets in vitro. These results suggest that, in a humanized in vivo model, CCL17 is sufficient per se to induce a lymph node recruitment of memory CD4+ and dendritic cells and a cutaneous recruitment of Th-2-type cells, stressing it as an important actor in the initiation and development of Th-2-associated skin inflammation.

Diesel exhaust exposure favors TH2 cell recruitment in nonatopic subjects by differentially regulating chemokine production.

BACKGROUND: The prevalence of allergic diseases has increased in the last 20 years, and a number of studies have shown that diesel exhaust particle-associated polyaromatic hydrocarbons can exacerbate the allergic reaction. Much less is known about their potential capacity to generate a T(H)2-type allergic reaction in nonatopic subjects. OBJECTIVE: The aim of this study was to test the hypothesis that diesel exhaust exposure might favor, in nonatopic donors, T(H)2-type cell recruitment, either through increased production of T(H)2-attracting chemokines or decreased production of T(H)1-attracting chemokines. METHODS: PBMCs from nonatopic donors were incubated with diesel exhaust particle-polyaromatic hydrocarbons, and the supernatants were evaluated for the presence of pro-T(H)1 chemokines (IFN-gamma-induced protein 10 and monokine Induced by IFN-gamma) and pro-T(H)2 chemokines (macrophage-derived chemokine, I-309, and pulmonary and activation-regulated chemokine) by means of ELISA. The functional effect was evaluated by using chemotaxis assays with polarized T(H)1 and T(H)2 cells. RESULTS: Diesel exhaust exposure of PBMCs from nonatopic donors induced a late increase after 48 hours in pulmonary and activation-regulated chemokine mediated by IL-13 and a decrease in IFN-gamma-induced protein 10 levels selectively at both the protein and mRNA levels. The functional effect of these chemokine variations resulted in an enhanced chemotaxis of T(H)2, but not T(H)1, cells. CONCLUSION: These findings show that diesel exhaust exposure might be involved in the genesis of allergic diseases by differentially regulating chemokines favoring the recruitment of T(H)2 cells in nonatopic subjects. CLINICAL IMPLICATIONS: Environmental factors, especially air pollution, might favor the genesis of allergic diseases.

CCR5 usage by CCL5 induces a selective leukocyte recruitment in human skin xenografts in vivo.

CCR5 is one of the major inflammatory chemokine receptors with potential therapeutical applications in humans. However, the redundancy of chemokines and their receptors, and the species specificity of chemokine receptor antagonists pose challenges to understanding of the role they play in pharmacological situations. To address this question, we used a humanized severe combined immunodeficient mouse model grafted with human skin and autologous leukocytes, and evaluated the effect of a blocking antibody against human CCR5, on CCL5-induced cutaneous leukocyte recruitment in vivo. At baseline, CCL5 induced a significant recruitment of T cells mainly of the memory phenotype, of monocytes/macrophages, eosinophils, and IFN-gamma(+) but not IL-4(+) and IL-5(+) cells. In vivo, anti-CCR5 antibody was able to almost completely inhibit the recruitment of monocytes/macrophages and T-helper (Th)1-type cells to inhibit partially the attraction of memory T cells, but had no effect on eosinophil infiltration, although all these cell types express other CCL5 binding chemokine receptors than CCR5. These results indicate that the in vivo environment regulates target cell specificity of CCL5 leading to differential cell recruitment, suggesting that antagonizing CCR5 receptor may be of therapeutic value in diseases such as acquired immuno deficiency syndrome, where CCL5/CCR5, monocytes, and Th1-type cells play a predominant role.

Involvement of CCL18 in allergic asthma.

Allergic asthma is associated with a pulmonary recruitment of Th type 2 cells, basophils, and eosinophils, mainly linked to chemokine production. CCL18 is a chemokine preferentially expressed in the lung, secreted by APCs, induced by Th2-type cytokines, and only present in humans. Therefore, CCL18 may be involved in allergic asthma. PBMC from asthmatics allergic to house dust mite cultured in the presence of Dermatophagoides pteronyssinus 1 (Der p 1) allergen secreted CCL18, 48 and 72 h after stimulation, whereas those from healthy donors did not. Part of CCL18 was directly derived from Der p 1-stimulated plasmacytoid dendritic cells, whereas the other part was linked to monocyte activation by IL-4 and IL-13 produced by Der p 1-stimulated T cells. In bronchoalveolar lavages from untreated asthmatic allergic patients, CCL18 was highly increased compared with controls. Functionally, CCL18 preferentially attracted in vitro-polarized Th2 cells and basophils, but not eosinophils and Th1 cells, and induced basophil histamine and intracellular calcium release. These data show a new function for CCL18, i.e., the recruitment of Th2 cells and basophils, and suggest that CCL18 may play a predominant role in allergic asthma.

Effect of diesel on chemokines and chemokine receptors involved in helper T cell type 1/type 2 recruitment in patients with asthma.

The objective of this study was to evaluate if diesel exhausts could favor helper T cell type (Th) 2-associated allergic reactions either through an increased production of Th2-associated chemokines and of their associated receptors or through a decrease of Th1-attracting chemokines and chemokine receptors. Diesel but not allergen exposure of peripheral blood mononuclear cells from subjects with allergy induced a release of I-309, whereas both diesel and Der p 1 induced an early but transient release of monokine induced by IFN-gamma and a late release of pulmonary and activation-regulated chemokine. Although both Th1- and Th2-attracting chemokines were induced, the resulting effect was an increased chemotactic activity on Th2 but not Th1 cells. Surprisingly, diesel induced a late increase in the expression of the Th1-associated CXC receptor 3 and CC receptor 5. T cell CXC receptor 3 upregulation was not associated with an increased migration to its ligands. These two antagonistic effects have been previously reported as a scavenger mechanism to clear chemokines. Altogether, these results suggest that diesel, even without allergen, may amplify a type 2 immune response but that it can also increase late Th1-associated chemokine receptor expression, perhaps as a scavenger mechanism to clear pro-Th1 chemokines and promote the Th2 pathway.

CCR3-blocking antibody inhibits allergen-induced eosinophil recruitment in human skin xenografts from allergic patients.

Eosinophil, basophil, and T helper 2 (TH2) cell recruitment into tissues is a characteristic feature of allergic diseases. These cells have in common the expression of the chemokine receptor CCR3, which may represent a specific pathway for their accumulation in vivo. Although animal models of allergic reactions are available, findings cannot always be extrapolated to man. To overcome these limitations, we have developed a humanized mouse model of allergic cutaneous reaction using severe combined immunodeficiency mice engrafted with skin and autologous peripheral blood mononuclear cells from allergic donors. Intradermal injection of the relevant allergen into human skin xenografts from allergic individuals induced a significant recruitment of human CD4(+) T cells, basophils, and TH2-type cytokine mRNA-expressing cells, as well as murine eosinophils. Human skin xenografts, atopic status, and autologous peripheral blood mononuclear cell reconstitution were all mandatory to induce the allergic reaction. Next, we addressed the role of CCR3 in the endogenous mechanisms involved in the inflammatory cell recruitment in this experimental model of allergic cutaneous reaction. In vivo administration of an anti-human CCR3-blocking antibody selectively reduced accumulation of eosinophils but not that of CD4(+) cells, basophils, or cells expressing mRNA for TH2-type cytokines. These findings establish a new in vivo model of humanized allergic reaction and suggest that eosinophil migration is mediated mainly through CCR3. Finally, these results suggest that this model might be useful to test human-specific antiallergic modulators.