Direct inhibition of T-cell responses by the Cryptococcus capsular polysaccharide glucuronoxylomannan

The major virulence factor of the pathogenic fungi Cryptococcus neoformans and C. gattii is the capsule. Glucuronoxylomannan (GXM), the major component of the capsule, is a high-molecular-weight polysaccharide that is shed during cryptococcosis and can persist in patients after successful antifungal therapy. Due to the importance of T cells in the anticryptococcal response, we studied the effect of GXM on the ability of dendritic cells (DCs) to initiate a T-cell response. GXM inhibited the activation of cryptococcal mannoprotein-specific hybridoma T cells and the proliferation of OVA-specific OT-II T cells when murine bone marrow-derived DCs were used as antigen-presenting cells. Inhibition of OT-II T-cell proliferation was observed when either OVA protein or OVA323-339 peptide was used as antigen, indicating GXM did not merely prevent antigen uptake or processing. We found that DCs internalize GXM progressively over time; however, the suppressive effect did not require DCs, as GXM directly inhibited T-cell proliferation induced by anti-CD3 antibody, concanavalin A, or phorbol-12-myristate-13-acetate/ionomycin. Analysis of T-cell viability revealed that the reduced proliferation in the presence of GXM was not the result of increased cell death. GXM isolated from each of the four major cryptococcal serotypes inhibited the proliferation of human peripheral blood mononuclear cells stimulated with tetanus toxoid. Thus, we have defined a new mechanism by which GXM can impart virulence: direct inhibition of T-cell proliferation. In patients with cryptococcosis, this could impair optimal cell-mediated immune responses, thereby contributing to the persistence of cryptococcal infections.     

Bursopentin (BP5) from chicken bursa of fabricius attenuates the immune function of dendritic cells

Bursopentine (BP5), a novel pentapeptide isolated from chicken bursa of fabricius, has been proved to have immunomodulatory effects on B and T lymphocytes, anti-oxidative stress on macrophages, and antiproliferation on tumor cells. However, the effects of BP5 on the immune function exhibited by dendritic cells (DCs), which are regarded as a major target for immunomodulators, remain unknown. In this study, we examined the effects of BP5 on the activation and maturation of murine bone marrow-derived DCs. Our results showed that BP5 significantly suppressed the secretion of lipopolysaccharide (LPS)-induced pro-inflammatory (TNF-α, IL-1β, IL-6 and IL-12p70) and anti-inflammatory (IL-10) cytokines by DCs, and this impact was not due to its cytotoxicity. Besides, BP5 reversed the morphological changes and attenuated the expression of phenotypic markers (MHC II, CD40, CD80 and CD86 molecules) in LPS-induced DCs. Furthermore, BP5 restored the decreased FITC-dextran uptake in LPS-treated DCs, arrested the LPS-induced migration of DCs and abrogated the promoting ability of LPS-induced DCs for allogeneic T cell proliferation. These findings show a new immunopharmacological capability of BP5 and provide a novel approach in the prevention and therapy of chronic inflammation and autoimmunity via abolishing the immune function of DCs.     

Migration of CD4 T cells and dendritic cells toward sphingosine 1-phosphate (S1P) is mediated by different receptor subtypes: S1P regulates the functions of murine mature dendritic cells via S1P receptor type 3

Dendritic cells (DCs) and lymphocytes are known to show a migratory response to the phospholipid mediator, sphingosine 1-phosphate (S1P). However, it is unclear whether the same S1P receptor subtype mediates the migration of lymphocytes and DCs toward S1P. In this study, we investigated the involvement of S1P receptor subtypes in S1P-induced migration of CD4 T cells and bone marrow-derived DCs in mice. A potent S1P receptor agonist, the (S)-enantiomer of FTY720-phosphate [(S)-FTY720-P], at 0.1 nM or higher and a selective S1P receptor type 1 (S1P(1)) agonist, SEW2871, at 0.1 muM or higher induced a dose-dependent down-regulation of S1P(1). The pretreatment with these compounds resulted in a significant inhibition of mouse CD4 T cell migration toward S1P. Thus, it is revealed that CD4 T cell migration toward S1P is highly dependent on S1P(1). Mature DCs, when compared with CD4 T cells or immature DCs, expressed a relatively higher level of S1P(3) mRNA. S1P at 10-1000 nM induced a marked migration and significantly enhanced the endocytosis of FITC-dextran in mature but not immature DCs. Pretreatment with (S)-FTY720-P at 0.1 microM or higher resulted in a significant inhibition of S1P-induced migration and endocytosis in mature DCs, whereas SEW2871 up to 100 microM did not show any clear effect. Moreover, we found that S1P-induced migration and endocytosis were at an extremely low level in mature DCs prepared from S1P(3)-knockout mice. These results indicate that S1P regulates migration and endocytosis of murine mature DCs via S1P(3) but not S1P(1).     

Splenic dendritic cells induced by oral antigen administration are important for the transfer of oral tolerance in an experimental model of asthma

Peripheral tolerance can be induced after the feeding of Ag, which is referred to as oral tolerance. We demonstrated in this study that the oral administration of OVA induced tolerance in an experimental model of asthma in mice, and investigated which cells function as the regulatory cells in the transfer of this oral tolerance. In OVA-fed mice, the percentage of eosinophils in bronchoalveolar lavage fluid, serum IgE levels, airway hyperresponsiveness, and mRNA levels of IL-13 and eotaxin were significantly lower than found in nonfed mice. Histological examination of lung tissue showed a suppression of the accumulation of inflammatory cells in the peribronchial area of OVA-fed mice. Feeding after the first immunization or between the first and the second immunization suppressed these findings, whereas feeding just before the airway Ag challenge did not. The suppression of disease in OVA-fed mice was successfully transferred by injection of whole spleen cells of OVA-fed mice. When CD11c+ dendritic cells (DCs) were removed from splenocytes, this transfer of suppression was completely abolished. The injection of splenic DCs purified from OVA-fed mice alone transferred the suppression, whereas the injection of splenic DCs from naive mice that were cocultured with OVA in vitro did not. These data suggest that not only CD4+ T cells, but also CD11c+ DCs induced by Ag feeding are important for the active transfer of oral tolerance in this murine experimental model of asthma.     

Potent inhibition of dendritic cell differentiation and maturation by vitamin D analogs

We show that the immunosuppressive effects of 1alpha, 25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) are due, in part, to inhibition of the T cell stimulatory functions of dendritic cells (DCs). Addition of 10(-12) and 10(-8) M 1alpha,25(OH)(2)D(3) to murine DC cultures resulted in a concentration-dependent reduction in levels of class II MHC and the co-stimulatory ligands B7-1, B7-2, and CD40 without affecting the number of DCs generated. Higher concentrations of 1alpha,25(OH)(2)D(3) reduced DC yield. The capacity of DCs to induce proliferation of purified allogeneic T cells was reduced by 1alpha,25(OH)(2)D(3). The vitamin D(3) analog, 1alpha,25(OH)(2)-16-ene-23-yne-26,27-hexafluoro-19-nor -D(3), exerted identical effects at 100-fold lower concentrations. Inhibition of DC maturation and stimulatory function was absent in cultures from mice genetically lacking vitamin D receptors (VDR). Vitamin D analogs effectively reduce DC function via VDR-dependent pathways.     

Chlamydia infection induces ICOS ligand-expressing and IL-10-producing dendritic cells that can inhibit airway inflammation and mucus overproduction elicited by allergen challenge in BALB/c mice

Our previous study has shown that the adoptive transfer of dendritic cells (DCs) freshly isolated from Chlamydia-infected mice (iIDCs), unlike those from control naive mice (iNDCs), can inhibit systemic and cutaneous eosinophilia induced by OVA exposure. In the present study, we examined the mechanism by which iIDC inhibits allergen-specific Th2 cell differentiation in vitro and in vivo. The study revealed that iIDCs exhibited higher surface expression of CD8alpha and the ICOS ligand (ICOS-L), as well as higher IL-10 and IL-12 production than iNDCs. In vitro DC:CD4(+) T cell coculture experiments showed that iIDCs could inhibit allergen-specific Th2 cell differentiation and that the inhibitory effect could be abolished by the blockage of IL-10 or IL-12 activity. More interestingly, the coblockade of IL-10 and the ICOS-L showed synergistic effect in enhancing allergen-driven Th2 cytokine production. Furthermore, adoptive transfer of iIDCs, but not iNDCs, to OVA sensitized mice significantly inhibited airway eosinophilia and mucus overproduction following intranasal challenge with OVA. Overall, the data demonstrate a critical role played by ICOS-L-expressing and IL-10-producing DCs from Chlamydia-infected mice in the infection-mediated inhibition of allergic responses.     

Airway activation of formyl peptide receptors inhibits Th1 and Th17 cell responses via inhibition of mediator release from immune and inflammatory cells and maturation of dendritic cells

Formyl peptide receptors (FPRs) are chemoattractant receptors that mediate inflammatory cell responses to infection. Recent evidence indicates that noneosinophilic asthma phenotypes can be developed by both Th1 and Th17 cell responses when exposed to LPS-containing allergens. In this study, we evaluated the effects of airway activation of FPRs by their synthetic agonist, Trp-Lys-Tyr-Met-Val-D-Met (W-peptide), on the development of Th1 and Th17 cell responses in a noneosinophilic asthma mouse model. A noneosinophilic asthma mouse model was generated by intranasal sensitization with 10 μg of LPS plus 75 μg of OVA on days 0, 1, 2, and 7. Mice were then challenged with 50 μg of OVA alone on days 14, 15, 21, and 22. W-peptide was administered during the sensitization period, and immune and inflammatory responses were evaluated after OVA challenge. Lung inflammation after OVA challenge was partly abolished by airway activation of FPRs during sensitization. Maturation of dendritic cells (DCs) and migration of DCs from the lung to lung-draining lymph nodes were inhibited by FPR activation. In addition, airway activation of FPRs inhibited allergen-specific T cell proliferation in the lymph nodes. Production of IL-12 and IL-6 (Th1- and Th17-polarizing cytokines) from lung DCs was decreased by airway activation of FPRs. This effect resulted in the inhibition of allergen-specific Th1 and Th17 cell responses. Airway activation of FPRs during sensitization effectively prevents the development of Th1 and Th17 cell responses induced by LPS-containing allergens via multiple mechanisms, such as inhibition of DC maturation and migration and the production of Th1- and Th7-polarizing cytokines.     

Vascular endothelial growth factor impairs the functional ability of dendritic cells through Id pathways

Vascular endothelial growth factor (VEGF) is an angiogenic cytokine that plays an important role in tumor growth and progression. Recent evidence suggests an alternate, albeit indirect, role of VEGF on host immune response to tumors. VEGF appears to diminish host immunity by altering the function of major antigen-presenting cells such as dendritic cells (DCs) [D.I. Gabrilovich, T. Ishida, S. Nadaf, J.E. Ohm, D.P. Carbone, Antibodies to vascular endothelial growth factor enhance the efficacy of cancer immunotherapy by improving endogenous dendritic cell function, Clin. Cancer Res. 5 (1999) 2963-2970, D. Gabrilovich, T. Ishida, T. Oyama, S. Ran, V. Kravtsov, S. Nadaf, D.P. Carbone, Vascular endothelial growth factor inhibits the development of dendritic cells and dramatically affects the differentiation of multiple hematopoietic lineages in vivo, Blood 92 (1998) 4150-4166, T. Oyama, S. Ran, T. Ishida, S. Nadaf, L. Kerr, D.P. Carbone, D.I. Gabrilovich, Vascular endothelial growth factor affects dendritic cell maturation through the inhibition of nuclear factor-kappa B activation in hemopoietic progenitor cells, J. Immunol. 160 (1998) 1224-1232.]. DCs are prime initiators of host immunity as they are known to activate both primary as well as secondary immune responses [J. Banchereau, F. Briere, C. Caux, J. Davoust, S. Lebecque, Y.J. Liu, B. Pulendran, K. Palucka, Immunobiology of dendritic cells, Ann. Rev. Immunol. 18 (2000) 767-811.]. However, the exact nature of how VEGF suppresses DC function is not fully clear. In this report, we show that DCs cultured in the presence of VEGF are less potent in stimulating antigen-specific T-cells. Furthermore, by using DCs derived from Id1(-/-) mice that are defective in Flt-1 signaling, we demonstrated that the inhibitory function of VEGF on DC function is most likely mediated by Flt-1. Thus, the role of VEGF in downregulating host immunity may highlight a unique role of VEGF in the pathogenesis of cancer.     

Dendritic cells loaded with exogenous antigen by electroporation can enhance MHC class I–mediated antitumor immunity

To develop an efficient antitumor immunotherapy, we have examined if dendritic cells (DCs) loaded with soluble antigens by electroporation present more antigens via the MHC (major histocompatibility complex) class I pathway, which mediate a cytotoxic T-cell response. DCs loaded with ovalbumin (OVA) by electroporation presented more MHC class I–restricted determinants compared with DCs pulsed with OVA. When electroporated DCs were pulsed with OVA for additional times, both MHC class I– and II–restricted presentation of OVA were increased compared with each single procedure, including electroporation or simple pulse. Immunization with DCs loaded with OVA by electroporation induced higher cytotoxicity of splenocytes to E.G7 cells, a clone of EL4 cells transfected with an OVA cDNA, than immunization with DCs pulsed with OVA. In the animal study, immunization with DCs loaded with OVA or tumor cell lysates by electroporation induced an effective antitumor immunity against tumor of E.G7 cells or Lewis lung carcinoma cells, respectively. In addition, immunization with DCs loaded with antigen by combination of electroporation and pulse, completely protected mice from tumor formation, and prolonged survival, in both tumor models. These results demonstrated that electroporation would be a useful way to enhance MHC class I–mediated antitumor immunity without functional deterioration, and that the combination of electroporation and pulse could be a simple and efficient antigen-loading method and consequently lead to induction of strong antitumor immunity.Abbreviations DCs dendritic cells - MHC major histocompatibility complex - OVA ovalbumin - TAA tumor-associated antigen - CTL cytotoxic T lymphocyte - LDH lactate dehydrogenase     

CpG-DNA aided cross-priming by cross-presenting B cells

Covalent linkage of immunostimulatory CpG-DNA to OVA (CpG-OVA complex) results in CpG-DNA-aided cross-presentation of OVA by dendritic cells (DCs). In this study, we analyzed the thesis that CpG-OVA complexes may be cross-presented by B cells to route internalized Ag into the class I MHC presentation pathway. First, we describe that conjugation of CpG-DNA to OVA enhances up to 40-fold internalization of OVA by B cells, which in turn generate the CD8 T cell epitope SIINFEKL complexed to MHC class I, albeit less efficiently than DCs. Furthermore, upon internalization, CpG-DNA conjugated to OVA stimulates B cells to up-regulate costimulatory molecules and cytokines including IL-12. Adoptive transfer of CpG-OVA complex-loaded wild-type B cells cross-primes naive CD8 T cells both in wild-type mice and in MyD88-deficient mice. Overall, these findings disclose attributes of B cells, including cross-presentation of exogenous Ag and cross-priming of naive CD8 T cells that hitherto have been considered as hallmarks restricted to DCs.     

Lung effector memory and activated CD4+ T cells display enhanced proliferation in surfactant protein A-deficient mice during allergen-mediated inflammation

Although many studies have shown that pulmonary surfactant protein (SP)-A functions in innate immunity, fewer studies have addressed its role in adaptive immunity and allergic hypersensitivity. We hypothesized that SP-A modulates the phenotype and prevalence of dendritic cells (DCs) and CD4(+) T cells to inhibit Th2-associated inflammatory indices associated with allergen-induced inflammation. In an OVA model of allergic hypersensitivity, SP-A(-/-) mice had greater eosinophilia, Th2-associated cytokine levels, and IgE levels compared with wild-type counterparts. Although both OVA-exposed groups had similar proportions of CD86(+) DCs and Foxp3(+) T regulatory cells, the SP-A(-/-) mice had elevated proportions of CD4(+) activated and effector memory T cells in their lungs compared with wild-type mice. Ex vivo recall stimulation of CD4(+) T cell pools demonstrated that cells from the SP-A(-/-) OVA mice had the greatest proliferative and IL-4-producing capacity, and this capability was attenuated with exogenous SP-A treatment. Additionally, tracking proliferation in vivo demonstrated that CD4(+) activated and effector memory T cells expanded to the greatest extent in the lungs of SP-A(-/-) OVA mice. Taken together, our data suggested that SP-A influences the prevalence, types, and functions of CD4(+) T cells in the lungs during allergic inflammation and that SP deficiency modifies the severity of inflammation in allergic hypersensitivity conditions like asthma.     

The relative efficiency of acquisition of MHC:peptide complexes and cross-presentation depends on dendritic cell type

Intercellular exchange of MHC molecules has been reported between many cells, including professional and nonprofessional APCs. This phenomenon may contribute to T cell immunity to pathogens. In this study, we addressed whether the transfer of MHC class I:peptide complexes between cells plays a role in T cell responses and compare this to conventional cross-presentation. We observed that dsRNA-matured bone marrow-derived dendritic cells (BMDCs) acquired peptide:MHC complexes from other BMDCs either pulsed with OVA(257-264) peptide, soluble OVA, or infected with a recombinant adenovirus expressing OVA. In addition, BMDCs were capable of acquiring MHC:peptide complexes from epithelial cells. Spleen-derived CD8alpha(+) and CD8alpha(-) dendritic cells (DCs) also acquired MHC:peptide complexes from BMDCs pulsed with OVA(257-264) peptide. However, the efficiency of acquisition by these ex vivo derived DCs is much lower than acquisition by BMDC. In all cases, the acquired MHC:peptide complexes were functional in that they induced Ag-specific CD8(+) T cell proliferation. The efficiency of MHC transfer was compared with cross-presentation for splenic CD8alpha(+) and CD8alpha(-) as well as BMDCs. CD8alpha(+) DCs were more efficient at inducing T cell proliferation when they acquired Ag via cross-presentation, the opposite was observed for BMDCs and splenic CD8alpha(-) DCs. We conclude from these observations that the relative efficiency of MHC transfer vs cross-presentation differs markedly between different DC subsets.     

Real-time imaging reveals that P2Y2 and P2Y12 receptor agonists are not chemoattractants and macrophage chemotaxis to complement C5a is phosphatidylinositol 3-kinase (PI3K)- and p38 mitogen-activated protein kinase (MAPK)-independent

Adenosine 5'-triphosphate (ATP) has been implicated in the recruitment of professional phagocytes (neutrophils and macrophages) to sites of infection and tissue injury in two distinct ways. First, ATP itself is thought to be a chemotactic "find me" signal released by dying cells, and second, autocrine ATP signaling is implicated as an amplifier mechanism for chemotactic navigation to end-target chemoattractants, such as complement C5a. Here we show using real-time chemotaxis assays that mouse peritoneal macrophages do not directionally migrate to stable analogs of ATP (adenosine-5'-(γ-thio)-triphosphate (ATPγS)) or its hydrolysis product ADP (adenosine-5'-(β-thio)-diphosphate (ADPβS)). HPLC revealed that these synthetic P2Y(2) (ATPγS) and P2Y(12) (ADPβS) receptor ligands were in fact slowly degraded. We also found that ATPγS, but not ADPβS, promoted chemokinesis (increased random migration). Furthermore, we found that photorelease of ATP or ADP induced lamellipodial membrane extensions. At the cell signaling level, C5a, but not ATPγS, activated Akt, whereas both ligands induced p38 MAPK activation. p38 MAPK and Akt activation are strongly implicated in neutrophil chemotaxis. However, we found that inhibitors of phosphatidylinositol 3-kinase (PI3K; upstream of Akt) and p38 MAPK (or conditional deletion of p38α MAPK) did not impair macrophage chemotactic efficiency or migration velocity. Our results suggest that PI3K and p38 MAPK are redundant for macrophage chemotaxis and that purinergic P2Y(2) and P2Y(12) receptor ligands are not chemotactic. We propose that ATP signaling is strictly autocrine or paracrine and that ATP and ADP may act as short-range "touch me" (rather than long-range find me) signals to promote phagocytic clearance via cell spreading.     

CD4-8- dendritic cells prime CD4+ T regulatory 1 cells to suppress antitumor immunity

It is clear that dendritic cells (DCs) are essential for priming of T cell responses against tumors. However, the distinct roles DC subsets play in regulation of T cell responses in vivo are largely undefined. In this study, we investigated the capacity of OVA-presenting CD4-8-, CD4+8-, or CD4-8+ DCs (OVA-pulsed DC (DC(OVA))) in stimulation of OVA-specific T cell responses. Our data show that each DC subset stimulated proliferation of allogeneic and autologous OVA-specific CD4+ and CD8+ T cells in vitro, but that the CD4-8- DCs did so only weakly. Both CD4+8- and CD4-8+ DC(OVA) induced strong tumor-specific CD4+ Th1 responses and fully protective CD8+ CTL-mediated antitumor immunity, whereas CD4-8- DC(OVA), which were less mature and secreted substantial TGF-beta upon coculture with TCR-transgenic OT II CD4+ T cells, induced the development of IL-10-secreting CD4+ T regulatory 1 (Tr1) cells. Transfer of these Tr1 cells, but not T cells from cocultures of CD4-8- DC(OVA) and IL-10-/- OT II CD4+ T cells, into CD4-8+ DC(OVA)-immunized animals abrogated otherwise inevitable development of antitumor immunity. Taken together, CD4-8- DCs stimulate development of IL-10-secreting CD4+ Tr1 cells that mediated immune suppression, whereas both CD4+8- and CD4-8+ DCs effectively primed animals for protective CD8+ CTL-mediated antitumor immunity.     

Regulation of dendritic cell function by insulin/IGF-1/PI3K/Akt signaling through klotho expression

Insulin or insulin-like growth factor 1 (IGF-1) promotes the activation of phosphoinositide 3 kinase (PI3K)/Akt signaling in immune cells including dendritic cells (DCs), the most potent professional antigen-presenting cells for naive T cells. Klotho, an anti-aging protein, participates in the regulation of the PI3K/Akt signaling, thus the Ca²⁺-dependent migration is reduced in klotho-deficient DCs. The present study explored the effects of insulin/IGF-1 on DC function through klotho expression. To this end, the mouse bone marrow cells were isolated and cultured with GM-CSF to attain bone marrow-derived DCs (BMDCs). Cells were treated with insulin or IGF-1 and followed by stimulating with lipopolysaccharides (LPS). Tumor necrosis factor (TNF)-α formation was examined by enzyme-linked immunosorbent assay (ELISA). Phagocytosis was analyzed by FITC-dextran uptake assay. The expression of klotho was determined by quantitative PCR, immunoprecipitation and western blotting. As a result, treatment of the cells with insulin/IGF-1 resulted in reducing the klotho expression as well as LPS-stimulated TNF-α release and increasing the FITC-dextran uptake but unaltering reactive oxygen species (ROS) production in BMDCs. The effects were abolished by using pharmacological inhibition of PI3K/Akt with LY294002 and paralleled by transfecting DCs with klotho siRNA. In conclusion, the regulation of klotho sensitive DC function by IGF-1 or insulin is mediated through PI3K/Akt signaling pathway in BMDCs.     

Yersinia enterocolitica YopP inhibits MAP kinase-mediated antigen uptake in dendritic cells

Yersinia enterocolitica (Ye) targets mouse dendritic cells (DCs) and inhibits their ability to trigger T cell activation. Here we have investigated whether Ye might interfere with antigen presentation in DCs. Infection of DCs with the Ye wild-type strain reduced OVA uptake by DCs as demonstrated by flow cytometry and confocal laser scan microscopy. In contrast, DCs infected with Yersinia outer protein P (YopP)-deficient mutant strain rapidly internalized OVA. Furthermore, transfection of DCs with YopP, but not with a cysteine protease deficient YopP-C172A mutant, reduced uptake of OVA. This finding suggests that YopP, a virulence factor of Ye, inhibits OVA uptake by DCs. By the use of MAPK inhibitors we provide evidence that YopP mediates reduction of OVA uptake by its ability to block MAPK signalling pathways in host cells. Using transferrin (Tf) as specific marker for clathrin-mediated endocytosis (CME) and lucifer yellow (LY) as specific marker for macropinocytosis (MP) we could show that YopP inhibits CME, whereas other Yops inhibit MP. In keeping with these data, activation and proliferation of OVA-specific T cells was reduced when DCs were treated with MAPK inhibitors. Together, our data demonstrate that (i) MAPK play an important role in antigen uptake by CME in DCs, and (ii) that YopP inhibits this pathway of antigen uptake in DCs, which might contribute to evasion of adaptive immunity.     

CD39 is the dominant Langerhans cell-associated ecto-NTPDase: modulatory roles in inflammation and immune responsiveness

CD39, the endothelial ecto-nucleoside triphosphate diphosphohydrolase (NTPDase), regulates vascular inflammation and thrombosis by hydrolyzing ATP and ADP. Although ecto-NTPDase activities have been used as a marker of epidermal dendritic cells (DCs) known as Langerhans cells, the identity and function of these activities remain unknown. Here we report that Langerhans cells in CD39-/- mice express no detectable ecto-NTPDase activity. Irritant chemicals triggered rapid ATP and ADP release from keratinocytes and caused exacerbated skin inflammation in CD39-/- mice. Paradoxically, T cell-mediated allergic contact hypersensitivity was severely attenuated in CD39-/- mice. As to mechanisms, T cells increased pericellular ATP concentrations upon activation, and CD39-/- DCs showed ATP unresponsiveness (secondary to P2-receptor desensitization) and impaired antigen-presenting capacity. Our results show opposing outcomes of CD39 deficiency in irritant versus allergic contact dermatitis, reflecting its diverse roles in regulating extracellular nucleotide-mediated signaling in inflammatory responses to environmental insults and DC-T cell communication in antigen presentation.