Specificity of CD200/CD200R pathway in LPS-induced lung inflammation

Introduction

At lung mucosal surfaces, immune cells must initiate inflammatory response against pathogen without inducing tissue damage. Loss of this equilibrium can lead to acute respiratory distress syndrome (ARDS), a severe lung inflammatory disease characterized by excessive inflammation and dysregulation of anti-inflammatory pathways.

Methods

To investigate the role of anti-inflammatory pathway CD200/CD200R in lung inflammatory response, we administered LPS intratracheally in CD200 KO and wild type (WT) rats. Inflammation was evaluated using bronchoalveolar lavage (BAL) cellularity. Lung injury was measured by total protein level in BAL fluid, and levels of proinflammatory cytokines (TNF, IL-6) and chemokines (CXCL2, CCL2) were determined in BAL supernatants. In a second series of experiments, recombinant CD200Fc was administered to KO rats to restore the anti-inflammatory response.

Results

At baseline, CD200 KO rats did not show sign of inflammation, however KO rats had lower number of alveolar macrophages. In addition, LPS administration induced greater pulmonary edema in CD200 KO rats. This was accompanied with a higher recruitment of neutrophils as well as levels of TNF, IL-6, CXCL2, and CCL2 in BAL compared to WT rats. CD200Fc administration in KO rats reduced neutrophil accumulation and TNF and CXCL2 levels in BAL. Interestingly, the increased inflammatory response of CD200 KO rats could be attributed to greater activation potential of alveolar macrophages with higher levels of ERK and P-ERK MAPK.

Conclusion

This study shows that lung inflammatory response is exacerbated in absence of CD200 in an experimental model of ARDS in rats. In addition, CD200/CD200R pathway shows selective regulation of acute lung inflammation and cannot completely abrogate the complex LPS-induced inflammatory response. However, addition of CD200 agonist in a multi-target therapy strategy could have beneficial impacts.

Exposure to the Gram-Negative Bacteria Pseudomonas aeruginosa Influences the Lung Dendritic Cell Population Signature by Interfering With CD103 Expression

Lung dendritic cells (DCs) are divided into two major populations, which include CD103⁺XCR1⁺ cDC1s and CD11b⁺Sirpα⁺ cDC2s. The maintenance of their relative proportions is dynamic and lung inflammation, such as caused by exposure to lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, can have a significant impact on the local cDC signature. Alterations in the lung cDC signature could modify the capacity of the immune system to respond to various pathogens. We consequently aimed to assess the impact of the Gram-negative bacteria Pseudomonas aeruginosa on lung cDC1 and cDC2 populations, and to identify the mechanisms leading to alterations in cDC populations. We observed that exposure to P. aeruginosa decreased the proportions of CD103⁺XCR1⁺ cDC1s, while increasing that of CD11b⁺ DCs. We identified two potential mechanisms involved in this modulation of lung cDC populations. First, we observed an increase in bone marrow pre-DC IRF4 expression suggesting a higher propensity of pre-DCs to differentiate towards the cDC2 lineage. This observation was combined with a reduced capacity of lung XCR1⁺ DC1s to express CD103. In vitro, we demonstrated that GM-CSF-induced CD103 expression on cDCs depends on GM-CSF receptor internalization and RUNX1 activity. Furthermore, we observed that cDCs stimulation with LPS or P. aeruginosa reduced the proportions of intracellular GM-CSF receptor and decreased RUNX1 mRNA expression. Altogether, these results suggest that alterations in GM-CSF receptor intracellular localization and RUNX1 signaling could be involved in the reduced CD103 expression on cDC1 in response to P. aeruginosa. To verify whether the capacity of cDCs to express CD103 following P. aeruginosa exposure impacts the immune response, WT and Cd103^-/- mice were exposed to P. aeruginosa. Lack of CD103 expression led to an increase in the number of neutrophils in the airways, suggesting that lack of CD103 expression on cDC1s could favor the innate immune response to this bacterium.

High FA2H and UGT8 transcript levels predict hydroxylated hexosylceramide accumulation in lung adenocarcinoma

Lung cancer causes more deaths than any other cancer. Sphingolipids encompass metabolically interconnected species whose balance has pivotal effects on proliferation, migration, and apoptosis. In this study, we paralleled quantification of sphingolipid species with quantitative (q)PCR analyses of metabolic enzymes in order to identify dysregulated routes of sphingolipid metabolism in different subtypes of lung cancers. Lung samples were submitted to histopathological reexamination in order to confirm cancer type/subtype, which included adenocarcinoma histological subtypes and squamous cell and neuroendocrine carcinomas. Compared with benign lesions and tumor-free parenchyma, all cancers featured decreased sphingosine-1-phosphate and SMs. qPCR analyses evidenced differential mechanisms leading to these alterations between cancer types, with neuroendocrine carcinomas upregulating SGPL1, but CERT1 being downregulated in adenocarcinomas and squamous cell carcinomas. 2-Hydroxyhexosylceramides (2-hydroxyHexCers) were specifically increased in adenocarcinomas. While UDP-glycosyltransferase 8 (UGT8) transcript levels were increased in all cancer subtypes, fatty acid 2-hydroxylase (FA2H) levels were higher in adenocarcinomas than in squamous and neuroendocrine carcinomas. As a whole, we report differing mechanisms through which all forms of lung cancer achieve low SM and lysosphingolipids. Our results also demonstrate that FA2H upregulation is required for the accumulation of 2-hydroxyHexCers in lung cancers featuring high levels of UGT8.

A sphingosine-1-phosphate receptor 1 agonist inhibits tertiary lymphoid tissue reactivation and hypersensitivity in the lung

Hypersensitivity pneumonitis is characterized by pulmonary accumulation of B-cell-rich tertiary lymphoid tissues (TLTs), which are alleged sites of amplification for antigen-specific responses. The sphingosine-1-phosphate receptor 1 (S1P₁) regulates key mechanisms underlying lymphoid tissue biology and its chemical modulation causes lymphocyte retention in lymph nodes. Given the putative immunopathogenic impact of lymphocyte accumulation in TLTs, we investigated whether or not chemical modulation of S1P₁ caused lymphocyte retention within TLTs in a model of hypersensitivity pneumonitis. Mice were exposed subchronically to Methanosphaera stadtmanae (MSS) in order to induce an hypersensitivity pneumonitis-like disease. MSS exposure induced B-cell-rich TLTs surrounded by S1P₁-positive microvessels. Upon MSS rechallenge, the S1P₁ agonist RP001 prevented the pulmonary increase of CXCL13, a chief regulator of B-cell recruitment in lymphoid tissues. This was associated with a complete inhibition of MSS rechallenge-induced TLT enlargement and with a 2.3-fold reduction of MSS-specific antibody titers in the lung. Interference with TLT reactivation was associated with a 77% reduction of neutrophil accumulation and with full inhibition of protein-rich leakage in the airways. Thus, an S1P₁ agonist hinders TLT enlargement upon antigenic rechallenge and inhibits key pathognomonic features of experimental hypersensitivity pneumonitis.

Amplification of Adipogenic Commitment by VSTM2A

Despite progress in our comprehension of the mechanisms regulating adipose tissue development, the nature of the factors that functionally characterize adipose precursors is still elusive. Defining the early steps regulating adipocyte development is needed for the generation of tools to control adipose tissue size and function. Here, we report the discovery of V-set and transmembrane domain containing 2A (VSTM2A) as a protein expressed and secreted by committed preadipocytes. VSTM2A expression is elevated in the early phases of adipogenesis in vitro and adipose tissue development in vivo. We show that VSTM2A-producing cells associate with the vasculature and express the common surface markers of adipocyte progenitors. Overexpression of VSTM2A induces adipogenesis, whereas its depletion impairs this process. VSTM2A controls preadipocyte determination at least in part by modulating BMP signaling and PPARγ2 activation. We propose a model in which VSTM2A is produced to preserve and amplify the adipogenic capability of adipose precursors.

FTY720 promotes pulmonary fibrosis when administered during the remodelling phase following a bleomycin-induced lung injury

Fibrosis complicates numerous pathologies including interstitial lung diseases. Sphingosine analogs such as FTY720 can alleviate lung injury-induced fibrosis in murine models. Contradictorily, FTY720 also promotes in vitro processes normally leading to fibrosis and high doses in vivo foster lung fibrosis by enhancing vascular leakage into the lung. The goal of this study was to determine the effect of low doses of FTY720 on lung fibrosis triggered by an acute injury in mice. We first defined the time-boundaries delimiting the inflammatory and remodelling phases of an injury elicited by bleomycin based on neutrophil counts, total lung capacity and lung stiffness. Thereafter, FTY720 (0.1 mg/kg) was delivered during either the inflammatory or the remodelling phases of bleomycin-induced injury. While FTY720 decreased fibrosis by 60% and lung stiffness by 28% when administered during the inflammatory phase, it increased fibrosis (2.1-fold) and lung stiffness (1.7-fold) when administered during the remodelling phase. FTY720-induced worsening of fibrosis was associated with an increased expression of connective tissue growth factor, but not with vascular leakage into the lung. Thus, the timing of FTY720 delivery following a bleomycin-induced lung injury determines pro-vs anti-fibrotic outcomes.

A Phosphorylatable Sphingosine Analog Induces Airway Smooth Muscle Cytostasis and Reverses Airway Hyperresponsiveness in Experimental Asthma

In asthma, excessive bronchial narrowing associated with thickening of the airway smooth muscle (ASM) causes respiratory distress. Numerous pharmacological agents prevent experimental airway hyperresponsiveness (AHR) when delivered prophylactically. However, most fail to resolve this feature after disease is instated. Although sphingosine analogs are primarily perceived as immune modulators with the ability to prevent experimental asthma, they also influence processes associated with tissue atrophy, supporting the hypothesis that they could interfere with mechanisms sustaining pre-established AHR. We thus assessed the ability of a sphingosine analog (AAL-R) to reverse AHR in a chronic model of asthma. We dissected the pharmacological mechanism of this class of agents using the non-phosphorylatable chiral isomer AAL-S and the pre-phosphorylated form of AAL-R (AFD-R) in vivo and in human ASM cells. We found that a therapeutic course of AAL-R reversed experimental AHR in the methacholine challenge test, which was not replicated by dexamethasone or the non-phosphorylatable isomer AAL-S. AAL-R efficiently interfered with ASM cell proliferation in vitro, supporting the concept that immunomodulation is not necessary to interfere with cellular mechanisms sustaining AHR. Moreover, the sphingosine-1-phosphate lyase inhibitor SM4 and the sphingosine-1-phosphate receptor antagonist VPC23019 failed to inhibit proliferation, indicating that intracellular accumulation of sphingosine-1-phosphate or interference with cell surface S1P₁/S1P₃ activation, are not sufficient to induce cytostasis. Potent AAL-R-induced cytostasis specifically related to its ability to induce intracellular AFD-R accumulation. Thus, a sphingosine analog that possesses the ability to be phosphorylated in situ interferes with cellular mechanisms that beget AHR.

Pulmonary CD103 expression regulates airway inflammation in asthma

Although CD103(+) cells recently emerged as key regulatory cells in the gut, the role of CD103 ubiquitous expression in the lung and development of allergic airway disease has never been studied. To answer this important question, we evaluated the response of Cd103(-/-) mice in two separate well-described mouse models of asthma (ovalbumin and house dust mite extract). Pulmonary inflammation was assessed by analysis of bronchoalveolar lavage content, histology, and cytokine response. CD103 expression was analyzed on lung dendritic cells and T cell subsets by flow cytometry. Cd103(-/-) mice exposed to antigens developed exacerbated lung inflammation, characterized by increased eosinophilic infiltration, severe tissue inflammation, and altered cytokine response. In wild-type mice exposed to house dust mite, CD103(+) dendritic cells are increased in the lung and an important subset of CD4(+) T cells, CD8(+) T cells, and T regulatory cells express CD103. Importantly, Cd103(-/-) mice presented a deficiency in the resolution phase of inflammation, which supports an important role for this molecule in the control of inflammation severity. These results suggest an important role for CD103 in the control of airway inflammation in asthma.

Treatment with a sphingosine analog after the inception of house dust mite-induced airway inflammation alleviates key features of experimental asthma

Background

In vivo phosphorylation of sphingosine analogs with their ensuing binding and activation of their cell-surface sphingosine-1-phosphate receptors is regarded as the main immunomodulatory mechanism of this new class of drugs. Prophylactic treatment with sphingosine analogs interferes with experimental asthma by impeding the migration of dendritic cells to draining lymph nodes. However, whether these drugs can also alleviate allergic airway inflammation after its onset remains to be determined. Herein, we investigated to which extent and by which mechanisms the sphingosine analog AAL-R interferes with key features of asthma in a murine model during ongoing allergic inflammation induced by Dermatophagoides pteronyssinus.

Methods

BALB/c mice were exposed to either D. pteronyssinus or saline, intranasally, once-daily for 10 consecutive days. Mice were treated intratracheally with either AAL-R, its pre-phosphorylated form AFD-R, or the vehicle before every allergen challenge over the last four days, i.e. after the onset of allergic airway inflammation. On day 11, airway responsiveness to methacholine was measured; inflammatory cells and cytokines were quantified in the airways; and the numbers and/or viability of T cells, B cells and dendritic cells were assessed in the lungs and draining lymph nodes.

Results

AAL-R decreased airway hyperresponsiveness induced by D. pteronyssinus by nearly 70%. This was associated with a strong reduction of IL-5 and IL-13 levels in the airways and with a decreased eosinophilic response. Notably, the lung CD4⁺ T cells were almost entirely eliminated by AAL-R, which concurred with enhanced apoptosis/necrosis in that cell population. This inhibition occurred in the absence of dendritic cell number modulation in draining lymph nodes. On the other hand, the pre-phosphorylated form AFD-R, which preferentially acts on cell-surface sphingosine-1-phosphate receptors, was relatively impotent at enhancing cell death, which led to a less efficient control of T cell and eosinophil responses in the lungs.

Conclusion

Airway delivery of the non-phosphorylated sphingosine analog, but not its pre-phosphorylated counterpart, is highly efficient at controlling the local T cell response after the onset of allergic airway inflammation. The mechanism appears to involve local induction of lymphocyte apoptosis/necrosis, while mildly affecting dendritic cell and T cell accumulation in draining lymph nodes.

Gene expression profiling distinguishes radiation-induced fibrosing alveolitis from alveolitis in mice

Thoracic cavity radiotherapy is limited by the development of alveolitis and fibrosis in susceptible patients. To define the response to 18 Gy pulmonary irradiation in mice at the gene expression level and to identify pathways that may influence the alveolitis and fibrosis phenotypes, expression profiling was undertaken. Male mice of three strains, A/J (late alveolitis response), C3H/HeJ (C3H, early alveolitis response) and C57BL/6J (B6, fibrosis response), were exposed to thoracic radiation and euthanized when moribund, and lung tissue gene expression was assessed with microarrays. The responses of A/J and C3H mice were more similar to each other (60% of differentially expressed genes detected in both strains) than to that of B6 mice (17% overlap). Pathway analysis revealed the expression of complement and of B-cell proliferation and activation genes to distinguish fibrosis from the alveolitis response and cytokine interactions and intracellular signaling differed between A/J and C3H mice. A genomic approach was used to identify specific pathways that likely contribute to the lung response to radiation as fibrosis or alveolitis in mice.

Radiation-induced lung response of AcB/BcA recombinant congenic mice

The genetic factors that influence the development of radiotherapy-induced lung disease are largely unknown. Herein we identified a strain difference in lung response to radiation wherein A/J mice developed alveolitis with increased levels of pulmonary mast cells and cells in bronchoalveolar lavage while the phenotype in C57BL/6J mice was fibrosis with fewer inflammatory cells. To identify genomic loci that may influence these phenotypes, we assessed recombinant congenic (RC) mice derived from the A/J and C57BL/6J strains for their propensity to develop alveolitis or fibrosis after 18 Gy whole-thorax irradiation. Mouse survival, lung histopathology and bronchoalveolar lavage cell types were recorded. Informative strains for each of mast cell influx, bronchoalveolar cell numbers, alveolitis and fibrosis were identified. In mice with the A/J strain background, the severity of alveolitis correlated with increased mast cell numbers while in C57BL/6J background strain mice fibrosis was correlated with the percentage of neutrophils in lavage. The data for RC mice support the association of specific inflammatory cells with the development of radiation-induced lung disease and provide informative strains with which to dissect the genetic basis of these complex traits.

Modulation of Kir4.2 rectification properties and pHi-sensitive run-down by association with Kir5.1

Inwardly rectifying K+ channels (Kir) comprise seven subfamilies that can be subdivided further on the basis of cytosolic pH (pHi) sensitivity, rectification strength and kinetics, and resistance to run-down. Although distinct residues within each channel subunit define these properties, heteromeric association with other Kir subunits can modulate them. We identified such an effect in the wild-type forms of Kir4.2 and Kir5.1 and used this to further understand how the functional properties of Kir channels relate to their structures. Kir4.2 and a Kir4.2-Kir5.1 fusion protein were expressed in HEK293 cells. Inward currents from Kir4.2 were stable over 10 min and pHi-insensitive (pH 6 to 8). Conversely, currents from Kir4.2-Kir5.1 exhibited a pHi-sensitive run-down at slightly acidic pHi. At pHi 7.2, currents in response to voltage steps positive to EK were essentially time independent for Kir4.2 indicating rapid block by Mg2+. Coexpression with Kir5.1 significantly increased the blocking time constant, and increased steady-state outward current characteristic of weak rectifiers. Recovery from blockade at negative potentials was voltage dependent and 2 to 10 times slower in the homomeric channel. These results show that Kir5.1 converts Kir4.2 from a strong to a weak rectifier, rendering it sensitive to pHi, and suggesting that Kir5.1 plays a role in fine-tuning Kir4.2 activity.

Loss of Kv and MaxiK currents associated with increased MRP1 expression in small cell lung carcinoma

Regulatory volume decrease and exocrine secretion studies suggest a functional relationship between K+ and organic anion efflux. To test the hypothesis that the expression of K+ channels and MRP1 is reciprocally related, we employed the patch clamp and RT-PCR techniques on weakly (H69) and strongly MRP1-expressing (H69AR) small cell lung cancer cells. H69AR cells do not express the time- and voltage-dependent delayed rectifying K+ current (Kv) reported earlier in H69 cells and confirmed here. About 80% of the Kv current in H69 cells inactivated at 0 mV, allowing us to identify other K+ currents present in these cells. Whole-cell currents from cells dialyzed and bathed in K-gluconate as the major ions exhibited inward rectification in both cell types. Inwardly rectifying (Kir) currents in both H69 and H69AR cells showed time-dependent activation and slow inactivation at large negative potentials. H69 cells also express a threefold larger Ca2+ -stimulated K+ -selective and iberiotoxin-sensitive current relative to H69AR cells. In excised inside-out patches exposed to 145 mM symmetrical K+ solutions, H69 cells expressed a voltage- and Ca2+ -sensitive large conductance (128 +/- 5 pS) K+ channel (MaxiK). MaxiK-like currents were not observed at the whole-cell or single-channel level in H69AR cells. RT-PCR identified MaxiKalpha transcripts in H69 but not H69AR cells. These results indicate that two K+ currents (MaxiK and Kv) and the organic anion transporter MRP1 are reciprocally expressed in H69 and H69AR cells.

Bleomycin-induced pulmonary fibrosis susceptibility genes in AcB/BcA recombinant congenic mice

The genetic basis of susceptibility to pulmonary fibrosis is largely unknown. Initially, in this study, loci regulating the response of bleomycin-induced pulmonary fibrosis were mapped using a set of recombinant congenic strains bred from pulmonary fibrosis-resistant A/J and susceptible C57BL/6J (B6) mice. Linkage was identified (logarithm of the odds score = 4.9) on chromosome 9, and other suggestive loci were detected. The putative loci included alleles from both the B6 and A/J strains as increasing the fibrosis response of congenic mice. Gene expression analysis with microarrays revealed 3,304 genes or expressed sequence tags to be differentially expressed (P < 0.01) in lung tissue between bleomycin-treated B6 and A/J mice, and 246 of these genes mapped to potential susceptibility loci. Pulmonary genes differentially expressed between bleomycin-treated B6 and A/J mice included those of heparin binding and extracellular matrix deposition pathways. A review of available genomic sequences revealed 809 (43% of total) genes in the linkage intervals to have variations predicted to alter the encoded proteins or their regulation, 68 (8.4%) of which were also differentially expressed. Genomic approaches were combined to produce a set of candidate genes that may influence susceptibility to bleomycin-induced pulmonary fibrosis in the A/J:B6 mouse model.

Contribution of a time-dependent and hyperpolarization-activated chloride conductance to currents of resting and hypotonically shocked rat hepatocytes

Hepatocellular Cl- flux is integral to maintaining cell volume and electroneutrality in the face of the many transport and metabolic activities that describe the multifaceted functions of these cells. Although a significant volume-regulated Cl- current (VRAC) has been well described in hepatocytes, the Cl- channels underlying the large resting anion conductance have not been identified. We used a combination of electrophysiological and molecular approaches to describe potential candidates for this conductance. Anion currents in rat hepatocytes and WIF-B and HEK293T cells were measured under patch electrode-voltage clamp. With K+-free salts of Cl- comprising the major ions externally and internally, hyperpolarizing steps between -40 and -140 mV activated a time-dependent inward current in hepatocytes. Steady-state activation was half-maximal at -63 mV and 28-38% of maximum at -30 to -45 mV, previously reported hepatocellular resting potentials. Gating was dependent on cytosolic Cl-, shifting close to 58 mV/10-fold change in Cl- concentration. Time-dependent inward Cl- currents and a ClC-2-specific RT-PCR product were also observed in WIF-B cells but not HEK293T cells. All cell types exhibited typical VRAC in response to dialysis with hypertonic solutions. DIDS (0.1 mM) inhibited the hepatocellular VRAC but not the inward time-dependent current. Antibodies against the COOH terminus of ClC-2 reacted with a protein between 90 and 100 kDa in liver plasma membranes. The results demonstrate that rat hepatocytes express a time-dependent inward Cl- channel that could provide a significant depolarizing influence in the hepatocyte.

Cutting edge: MHC class II-restricted peptides containing the inflammation-associated marker 3-nitrotyrosine evade central tolerance and elicit a robust cell-mediated immune response

Nitrotyrosine is widely recognized as a surrogate marker of up-regulated inducible NO synthase expression at sites of inflammation. However, the potential immunogenicity of autologous proteins containing nitrotyrosine has not previously been investigated. Herein, we used the I-E(K)-restricted T cell epitope of pigeon/moth cytochrome c (PCC/MCC(88-103)) to assess the ability of T cells to recognize ligands containing nitrotyrosine. Substitution of the single tyrosine (Y97) in PCC/MCC(88-103) with nitrotyrosine abrogates recognition by the MCC(88-103)-specific T cell hybridoma 2B4. CBA (H2(K)) mice immunized with MCC(88-103) or nitrated MCC(88-103) peptides produce T cell responses that are mutually exclusive. Transgenic mice that constitutively express PCC under the control of an MHC class I promoter are tolerant toward immunization with MCC(88-103), but exhibited a robust immune response against nitrated MCC(88-103). Analysis of T cell hybridomas specific for nitrated-MCC(88-103) indicated that subtle differences in TCR VDJ gene usage are sufficient to allow nitrotyrosine-specific T cells to escape the processes of central tolerance.

"Bystander polarization" of CD4+ T cells: activation with high-dose IL-2 renders naive T cells responsive to IL-12 and/or IL-18 in the absence of TCR ligation

Responsiveness of CD4+ T cells to the IFN-gamma-inducing cytokines IL-12 and IL-18 is generally thought to be acquired only after stimulation via the TCR. We report herein that stimulation of naive CD4+ T cells with high-dose IL-2 (1000 U/ml) renders these cells responsive to IL-12 and/or IL-18 without a requirement for TCR ligation. Naive CD4+CD62L+ Tcells from normal C57BL/6 mice or from DO11.10/Rag2(-/- )OVA-specific TCR-transgenic mice secreted substantial amounts of IFN-gamma when stimulated concurrently with high-dose IL-2 plus IL-12 or IL-18. mRNA encoding both chains of the IL-12 and the IL-18 receptors was expressed by CD4+ T cells after stimulation with high-dose IL-2. Furthermore, anti-CD3-induced IL-12/IL-18 responsiveness was fully abrogated in the presence of cyclosporin A whereas IL-2-induced IL-12/IL-18 responsiveness was not, reminiscent of the previously reported IL-12+IL-18 innate pathway of T cell activation. Lastly, after stimulation with IL-2+IL-12, naive CD4+ T cells from DO11.10/Rag2(-/- )mice exhibited polarization towards a Th1 phenotype (high IFN-gamma but no IL-4) during secondary stimulation with immobilized anti-CD3. We have coined the term "bystander polarization" to describe this phenomenon and we speculate that bystander polarization of naive CD4+ T cells may occur in vivo during strong antigen-specific immune responses.

Cytokine expression by murine DX5+ cells in response to IL-12, IL-18, or the combination of IL-12 and IL-18

In this study we analyzed the response of DX5+ NK and NK T cells to in vitro stimulation with IL-12 or IL-18. Production of IFN-gamma in response to either IL-12 or IL-18 was dependent upon costimulation with either IL-2 or IL-15. DX5+ splenocytes showed a rapid (6 h) and sustained (6-72 h) accumulation of IFN-gamma transcripts followed by a delayed (12-24 h) up-regulation of IL-10 or IL-13 expression in response to IL-2 + IL-12 or IL-2 + IL-18, respectively. Incubation of DX5+ splenocytes with the combination of IL-2 + IL-12 + IL-18 resulted in up-regulation of IFN-gamma and IL-13 transcripts but down-regulation of IL-10 expression. Furthermore, two distinct populations of cells producing differing amounts of IFN-gamma were observed by intracellular staining after stimulation with IL-2 + IL-12 + IL-18. Last, we demonstrate that DX5+ cells respond to IL-18 independently of IL-12, as cells from both wild-type and IL-12Rbeta2KO mice produce IFN-gamma and IL-13 in response to IL-2 + IL-18.