Cigarette smoke disrupts VEGF165-VEGFR-2 receptor signaling complex in rat lungs and patients with COPD: morphological impact of VEGFR-2 inhibition

VEGF is fundamental in the development and maintenance of the vasculature. VEGF(165) signaling through VEGF receptor (VEGFR)-2/kinase insert domain receptor (KDR) is a highly regulated process involving the formation of a tertiary complex with glypican (GYP)-1 and neuropilin (NRP)-1. Both VEGF and VEGFR-2 expression are reduced in emphysematous lungs; however, the mechanism of regulation of VEGF(165) signaling through the VEGFR-2 complex in response to cigarette smoke exposure in vivo, and in smokers with and without chronic obstructive pulmonary disease (COPD), is still unknown. We hypothesized that cigarette smoke exposure disrupts the VEGF(165)-VEGFR-2 complex, a potential mechanism in the pathogenesis of emphysema. We show that cigarette smoke exposure reduces NRP-1 and GYP-1 as well as VEGF and VEGFR-2 levels in rat lungs and that VEGF, VEGFR-2, GYP-1, and NRP-1 expression in the lungs of both smokers and patients with COPD are also reduced compared with nonsmokers. Moreover, our data suggest that specific inhibition of VEGFR-2 alone with NVP-AAD777 would appear not to result in emphysema in the adult rat lung. As both VEGF(165) and VEGFR-2 expression are reduced in emphysematous lungs, decreased GYP-1 and NRP-1 expression may yet further disrupt VEGF(165)-VEGFR-2 signaling. Whether or not this by itself is critical for inducing endothelial cell apoptosis and decreased vascularization of the lung seen in emphysema patients is still unclear at present. However, targeted therapies to restore VEGF(165)-VEGFR-2 complex may promote endothelial cell survival and help to ameliorate emphysema.     

Inhibition of xanthine oxidase reduces hyperglycemia-induced oxidative stress and improves mitochondrial alterations in skeletal muscle of diabetic mice

Reactive oxygen species (ROS) have been widely implicated in the pathogenesis of diabetes and more recently in mitochondrial alterations in skeletal muscle of diabetic mice. However, so far the exact sources of ROS in skeletal muscle have remained elusive. Aiming at better understanding the causes of mitochondrial alterations in diabetic muscle, we designed this study to characterize the sites of ROS production in skeletal muscle of streptozotocin (STZ)-induced diabetic mice. Hyperglycemic STZ mice showed increased markers of systemic and muscular oxidative stress, as evidenced by increased circulating H(2)O(2) and muscle carbonylated protein levels. Interestingly, insulin treatment reduced hyperglycemia and improved systemic and muscular oxidative stress in STZ mice. We demonstrated that increased oxidative stress in muscle of STZ mice is associated with an increase of xanthine oxidase (XO) expression and activity and is mediated by an induction of H(2)O(2) production by both mitochondria and XO. Finally, treatment of STZ mice, as well as high-fat and high-sucrose diet-fed mice, with oxypurinol reduced markers of systemic and muscular oxidative stress and prevented structural and functional mitochondrial alterations, confirming the in vivo relevance of XO in ROS production in diabetic mice. These data indicate that mitochondria and XO are the major sources of hyperglycemia-induced ROS production in skeletal muscle and that the inhibition of XO reduces oxidative stress and improves mitochondrial alterations in diabetic muscle.     

Smooth muscle-specific expression of calcium-independent phospholipase A2β (iPLA2β) participates in the initiation and early progression of vascular inflammation and neointima formation

Whether group VIA phospholipase A(2) (iPLA(2)β) is involved in vascular inflammation and neointima formation is largely unknown. Here, we report that iPLA(2)β expression increases in the vascular tunica media upon carotid artery ligation and that neointima formation is suppressed by genetic deletion of iPLA(2)β or by inhibiting its activity or expression via perivascular delivery of bromoenol lactone or of antisense oligonucleotides, respectively. To investigate whether smooth muscle-specific iPLA(2)β is involved in neointima formation, we generated transgenic mice in which iPLA(2)β is expressed specifically in smooth muscle cells and demonstrate that smooth muscle-specific expression of iPLA(2)β exacerbates ligation-induced neointima formation and enhanced both production of proinflammatory cytokines and vascular infiltration by macrophages. With cultured vascular smooth muscle cell, angiotensin II, arachidonic acid, and TNF-α markedly induce increased expression of IL-6 and TNF-α mRNAs, all of which were suppressed by inhibiting iPLA(2)β activity or expression with bromoenol lactone, antisense oligonucleotides, and genetic deletion, respectively. Similar suppression also results from genetic deletion of 12/15-lipoxygenase or inhibiting its activity with nordihydroguaiaretic acid or luteolin. Expression of iPLA(2)β protein in cultured vascular smooth muscle cells was found to depend on the phenotypic state and to rise upon incubation with TNF-α. Our studies thus illustrate that smooth muscle cell-specific iPLA(2)β participates in the initiation and early progression of vascular inflammation and neointima formation and suggest that iPLA(2)β may represent a novel therapeutic target for preventing cardiovascular diseases.     

The SGLT2 inhibitor Empagliflozin attenuates interleukin-17A-induced human aortic smooth muscle cell proliferation and migration by targeting TRAF3IP2/ROS/NLRP3/Caspase-1-dependent IL-1β and IL-18 secretion

Chronic inflammation and persistent oxidative stress contribute to the development and progression of vascular proliferative diseases. We hypothesized that the proinflammatory cytokine interleukin (IL)-17A induces oxidative stress and amplifies inflammatory signaling in human aortic smooth muscle cells (SMC) via TRAF3IP2-mediated NLRP3/caspase-1-dependent mitogenic and migratory proinflammatory cytokines IL-1β and IL-18. Further, we hypothesized that these maladaptive changes are prevented by empagliflozin (EMPA), an SGLT2 (Sodium/Glucose Cotransporter 2) inhibitor. Supporting our hypotheses, exposure of cultured SMC to IL-17A promoted proliferation and migration via TRAF3IP2, TRAF3IP2-dependent superoxide and hydrogen peroxide production, NLRP3 expression, caspase-1 activation, and IL-1β and IL-18 secretion. Furthermore, NLRP3 knockdown, caspase-1 inhibition, and pretreatment with IL-1β and IL-18 neutralizing antibodies and IL-18BP, each attenuated IL-17A-induced SMC migration and proliferation. Importantly, SMC express SGLT2, and pre-treatment with EMPA attenuated IL-17A/TRAF3IP2-dependent oxidative stress, NLRP3 expression, caspase-1 activation, IL-1β and IL-18 secretion, and SMC proliferation and migration. Importantly, silencing SGLT2 attenuated EMPA-mediated inhibition of IL-17A-induced cytokine secretion and SMC proliferation and migration. EMPA exerted these beneficial antioxidant, anti-inflammatory, anti-mitogenic and anti-migratory effects under normal glucose conditions and without inducing cell death. These results suggest the therapeutic potential of EMPA in vascular proliferative diseases.     

Neuropilin-1 forms complexes with vascular endothelial growth factor receptor-2 during megakaryocytic differentiation of UT-7/TPO cells

We investigated whether the gene expression of vascular endothelial growth factor (VEGF) and its receptors (VEGFR and neuropilin-1 [NRP-1]) could be specifically regulated during the megakaryocytic differentiation of human thrombopoietin (TPO)-dependent UT-7/TPO cells. Undifferentiated UT-7/TPO cells expressed a functional VEGFR-2, leading to VEGF binding and VEGF₁₆₅-induced tyrosine phosphorylation, cell proliferation, and apoptosis inhibition. The megakaryocytic differentiation of UT-7/TPO cells on treatment with phorbol myristate acetate (PMA) was accompanied by a marked up-regulation of NRP-1 mRNA and protein expression and by an increase in VEGF-binding activity, which was mainly mediated by VEGFR-2. VEGF₁₆₅ promoted the formation of complexes containing NRP-1 and VEGFR-2 in undifferentiated UT-7/TPO cells in a dose-dependent manner. Unlike human umbilical vein endothelial cells, PMA-differentiated UT-7/TPO cells exhibited complex formation between NRP-1 and VEGFR-2 even in the absence of VEGF₁₆₅. These findings suggest that NRP-1-VEGFR-2-complex formation may contribute to effective cellular functions mediated by VEGF₁₆₅ in megakaryocytic cells.     

Role of macrophages in inflammatory lymphangiogenesis: Enhanced production of vascular endothelial growth factor C and D through NF-kappaB activation

The close association of inflammation, angiogenesis and cancer progression is now highlighted, and in this study we especially focused on a close association of inflammation and lymphangiogenesis. We found that proinflammatory cytokine, interleukin-1β (IL-1β), could induce lymphangiogenesis in mouse cornea through enhanced production of potent lymphangiogenic factors, VEGF-A, VEGF-C and VEGF-D. IL-1β-induced lymphangiogenesis, but not angiogenesis, was inhibited by administration of a selective anti-VEGF receptor-3 (VEGFR-3) neutralizing antibody. And in mouse cornea we observed recruitment of monocyte/macrophages and neutrophils by IL-1β implanted cornea. Depletion of macrophages by a bisphosphonate encapsulated in liposomes inhibited this IL-1β-induced lymphangiogenesis and also up-regulation of VEGF-A, VEGF-C, and VEGF-D. Furthermore, IL-1β-induced lymphangiogenesis and angiogenesis were suppressed by NF-κB inhibition with marked suppression of VEGF-A, VEGF-C, and VEGF-D expression.     

Notch, IL-1 and leptin crosstalk outcome (NILCO) is critical for leptin-induced proliferation, migration and VEGF/VEGFR-2 expression in breast cancer

High levels of pro-angiogenic factors, leptin, IL-1, Notch and VEGF (ligands and receptors), are found in breast cancer, which is commonly correlated with metastasis and lower survival of patients. We have previously reported that leptin induces the growth of breast cancer and the expression of VEGF/VEGFR-2 and IL-1 system. We hypothesized that Notch, IL-1 and leptin crosstalk outcome (NILCO) plays an essential role in the regulation of leptin-mediated induction of proliferation/migration and expression of pro-angiogenic molecules in breast cancer. To test this hypothesis, leptin's effects on the expression and activation of Notch signaling pathway and VEGF/VEGFR-2/IL-1 were determined in mouse (4T1, EMT6 and MMT) breast cancer cells. Remarkably, leptin up-regulated Notch1-4/JAG1/Dll-4, Notch target genes: Hey2 and survivin, together with IL-1 and VEGF/VEGFR-2. RNA knockdown and pharmacological inhibitors of leptin signaling significantly abrogated activity of reporter gene-luciferase CSL (RBP-Jk) promoter, showing that it was linked to leptin-activated JAK2/STAT3, MAPK, PI-3K/mTOR, p38 and JNK signaling pathways. Interestingly, leptin upregulatory effects on cell proliferation/migration and pro-angiogenic factors Notch, IL-1 and VEGF/VEGFR-2 were abrogated by a γ-secretase inhibitor, DAPT, as well as siRNA against CSL. In addition, blockade of IL-1R tI inhibited leptin-induced Notch, Hey2 and survivin as well as VEGF/VEGFR-2 expression. These data suggest leptin is an inducer of Notch (expression/activation) and IL-1 signaling modulates leptin effects on Notch and VEGF/VEGFR-2. We show for the first time that a novel unveiled crosstalk between Notch, IL-1 and leptin (NILCO) occurs in breast cancer. Leptin induction of proliferation/migration and upregulation of VEGF/VEGFR-2 in breast cancer cells were related to an intact Notch signaling axis. NILCO could represent the integration of developmental, pro-inflammatory and pro-angiogenic signals critical for leptin-induced cell proliferation/migration and regulation of VEGF/VEGFR-2 in breast cancer. Targeting NILCO might help to design new pharmacological strategies aimed at controlling breast cancer growth and angiogenesis.     

Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.     

New molecular mechanisms of the unexpectedly complex role of VEGF in ulcerative colitis

The effects of VEGF on endothelial cells are mediated by different intracellular signaling cascades (e.g., Erk1/2, Akt, Src). VEGF plays a recently recognized role in ulcerative colitis (UC) pathogenesis, mostly by increasing vascular permeability and promoting the infiltration of inflammatory cells. We hypothesized that the excessive activation of signal transduction pathways, which is responsible for VEGF/VEGFR-2-mediated endothelial permeability (Src, Akt), is a new element in the pathogenesis of chronic UC. We demonstrated increased expression of pro-angiogenic growth factor VEGF and its receptor VEGFR-2 in colonic tissue during acute 6% iodoacetamide-induced UC in rats and chronic spontaneously developed UC in IL-10 knockout mice (IL-10 KO). Development of acute 6% iodoacetamide-induced UC in rats was accompanied by activation of Erk1/2 and Src kinase, while expression of total proteins Erk1/2 and Src was unchanged. During chronic colitis phosphorylation (i.e., activation) of Erk1/2 was significantly decreased in IL-10 KO mice vs. wild-type mice. Levels of total Erk1/2 proteins were unchanged, but the expression of total Src protein as well as its phosphorylated form was significantly increased in IL-10 KO vs. wild-type mice. There were no changes in total Akt proteins, while levels of activated Akt (pAkt) were slightly increased in IL-10 KO vs. wild-type mice. We conclude that VEGF/VEGFR-2-associated signal transduction pathways, that mediate increased vascular permeability (Src, Akt), might play a central role in perpetuation of chronic experimental UC.     

Central role of endogenous Toll-like receptor-2 activation in regulating inflammation, reactive oxygen species production, and subsequent neointimal formation after vascular injury

Background

It is now evident that inflammation after vascular injury has significant impact on the restenosis after revascularization procedures such as angioplasty, stenting, and bypass grafting. However, the mechanisms that regulate inflammation and repair after vascular injury are incompletely understood. Here, we report that vascular injury-mediated cytokine expression, reactive oxygen species (ROS) production, as well as subsequent neointimal formation requires Toll-like receptor-2 (TLR-2) mediated signaling pathway in vivo.

Methods and results

Vascular injury was induced by cuff-placement around the femoral artery in non-transgenic littermates (NLC) and TLR-2 knockout (TLR-2KO) mice. After cuff-placement in NLC mice, expression of TLR-2 was significantly increased in both smooth muscle medial layer and adventitia. Interestingly, we found that inflammatory genes expression such as tumor necrosis factor-α, interleukin-1β (IL-1β), IL-6, and monocyte chemoattractant protein-1 were markedly decreased in TLR-2KO mice compared with NLC mice. In addition, ROS production after vascular injury was attenuated in TLR-2KO mice compared with NLC mice. Since we observed the significant role of endogenous TLR-2 activation in regulating inflammatory responses and ROS production after vascular injury, we determined whether inhibition of endogenous TLR-2 activation can inhibit neointimal proliferation after vascular injury. Neointimal hyperplasia was markedly suppressed in TLR-2KO mice compared with WT mice at both 2 and 4 weeks after vascular injury.

Conclusions

These findings suggested that endogenous TLR-2 activation might play a central role in the regulation of vascular inflammation as well as subsequent neointimal formation in injured vessels.     

Interleukin-1β and mitochondria damage, and the development of diabetic retinopathy

Mitochondrial dysfunction is considered to play an important role in the development of diabetic retinopathy. Recent evidence has also shown many similarities between diabetic retinopathy and a low grade chronic inflammatory disease. The aim of this study is to understand the interrelationship between proinflammtory mediator, IL-1β and mitochondrial dysfunction in the accelerated loss of capillary cells in the retina. Using IL-1β receptor gene knockout (IL-1R1^?/^?) diabetic mice, we have investigated the effect of regulation of IL-1β on mitochondrial dysfunction and mtDNA damage, and increased retinal capillary cell apoptosis and the development of retinopathy. Retinal mitochondrial dysfunction and mtDNA damage were significantly ameliorated in IL-1R1^?/^? mice, diabetic for ~10 months, compared to the wild-type diabetic mice. This was accompanied by protection of accelerated capillary cell apoptosis and the development of acellular capillaries, histopathology associated with diabetic retinopathy. Thus, mitochondrial damage could be one of the key events via which increased inflammation contributes to the activation of the apoptotic machinery resulting in the development of diabetic retinopathy, and the possible mechanism via which inflammation contributes to the development of diabetic retinopathy includes continuous fueling of the vicious cycle of mitochondrial damage, which could be disrupted by inhibitors of inflammatory mediators.     

Soluble DPP4 induces inflammation and proliferation of human smooth muscle cells via protease-activated receptor 2

DPP4 is an ubiquitously expressed cell-surface protease that is shedded to the circulation as soluble DPP4 (sDPP4). We recently identified sDPP4 as a novel adipokine potentially linking obesity to the metabolic syndrome. The aim of this study was to investigate direct effects of sDPP4 on human vascular smooth muscle cells (hVSMCs) and to identify responsible signaling pathways. Using physiological concentrations of sDPP4, we could observe a concentration-dependent activation of ERK1/2 (3-fold) after 6 h, which remained stable for up to 24 h. Additionally, sDPP4 treatment induced a 1.5-fold phosphorylation of the NF-κB subunit p65. In accordance with sDPP4-induced stress and inflammatory signaling, sDPP4 also stimulates hVSMC proliferation. Furthermore we could observe an increased expression and secretion of pro-inflammatory cytokines like interleukin (IL)-6, IL-8 and MCP-1 (2.5-, 2.4- and 1.5-fold, respectively) by the sDPP4 treatment. All direct effects of sDPP4 on signaling, proliferation and inflammation could completely be prevented by DPP4 inhibition. Bioinformatic analysis and signaling signature induced by sDPP4 suggest that sDPP4 might be an agonist for PAR2. After the silencing of PAR2, the sDPP4-induced ERK activation as well as the proliferation was totally abolished. Additionally, the sDPP4-induced upregulation of IL-6 and IL-8 could completely be prevented by the PAR2 silencing. In conclusion, we show for the first time that sDPP4 directly activates the MAPK and NF-κB signaling cascade involving PAR2 and resulting in the induction of inflammation and proliferation of hVSMC. Thus, our in vitro data might extend the current view of sDPP4 action and shed light on cardiovascular effects of DPP4-inhibitors.     

NLRP3/caspase-1-independent IL-1beta production mediates diesel exhaust particle-induced pulmonary inflammation

Inhalation of diesel exhaust particles (DEP) induces an inflammatory reaction in the lung; however, the mechanisms are largely unclear. IL-1β/IL-1RI signaling is crucial in several lung inflammatory responses. Typically, caspase-1 is activated within the NLRP3 inflammasome that recognizes several damage-associated molecular patterns, which results in cleavage of pro-IL-1β into mature IL-1β. In this study, we hypothesized that the NLRP3/caspase-1/IL-1β pathway is critical in DEP-induced lung inflammation. Upon DEP exposure, IL-1RI knockout mice had reduced pulmonary inflammation compared with wild-type mice. Similarly, treatment with rIL-1R antagonist (anakinra) and IL-1β neutralization impaired the DEP-induced lung inflammatory response. Upon DEP exposure, NLRP3 and caspase-1 knockout mice, however, showed similar IL-1β levels and comparable pulmonary inflammation compared with wild-type mice. In conclusion, these data show that the DEP-induced pulmonary inflammation acts through the IL-1β/IL-1RI axis. In addition, DEP initiates inflammation independent of the classical NLRP3/caspase-1 pathway, suggesting that other proteases might be involved.     

Curcumin ameliorates CKD-induced mitochondrial dysfunction and oxidative stress through inhibiting GSK-3β activity

Curcumin has been reported to attenuate muscle atrophy. However, the underling mechanism remains unclear. The aim of this study was to investigate whether curcumin could improve chronic kidney disease (CKD)-induced muscle atrophy and mitochondrial dysfunction by inhibiting glycogen synthase kinase-3β (GSK-3β) activity. The sham and CKD mice were fed either a control diet or an identical diet containing 0.04% curcumin for 12 weeks. The C2C12 myotubes were treated with H₂O₂ in the presence or absence of curcumin. In addition, wild-type and muscle-specific GSK-3β knockout (KO) CKD model mice were made by 5/6 nephrectomy, and the sham was regarded as control. Curcumin could exert beneficial effects, including weight maintenance and improved muscle function, increased mitochondrial biogenesis, alleviated mitochondrial dysfunction by increasing adenosine triphosphate levels, activities of mitochondrial electron transport chain complexes and basal mitochondrial respiration and suppressing mitochondrial membrane potential. In addition, curcumin modulated redox homeostasis by increasing antioxidant activity and suppressed mitochondrial oxidative stress. Moreover, the protective effects of curcumin had been found to be mediated via inhibiting GSK-3β activity in vitro and in vivo. Importantly, GSK-3β KO contributed to improved mitochondrial function, attenuated mitochondrial oxidative damage and augmented mitochondrial biogenesis in muscle of CKD. Overall, this study suggested that curcumin alleviated CKD-induced mitochondrial oxidative damage and mitochondrial dysfunction via inhibiting GSK-3β activity in skeletal muscle.     

坏死细胞释放IL-1β对血管平滑肌细胞侵袭和迁移的影响及机制研究

目的研究坏死血管平滑肌细胞释放IL-1β对周围正常细胞侵袭和迁移的影响,并探讨其可能的机制。方法无血清低糖低氧条件下培养细胞,建立细胞坏死模型,收集坏死细胞培养上清液,用于干预正常血管平滑肌细胞。实验设坏死上清组（NCS）、IL-1β组、NCS＋IL-1RA组和对照组（Control）。Tran-swell小室实验和细胞划痕实验检测各组细胞侵袭和迁徙能力,RT-PCR和Western印迹检测各组MMP-2和MMP-9的表达,Western印迹检测各组NF-κB的激活情况。结果NCS组和IL-1β组细胞侵袭和迁移能力均显著高于对照组（P〈0．05）,NCS＋IL-1RA组细胞侵袭和迁移能力显著低于NCS组和IL-1组（P〈0．05）;对照组和NCS＋IL．1RA组NF-κB、MMP-2和MMP-9均显著低于NCS组和IL-1β组（P〈0．05）,IκB显著高于NCS组和IL-1β组（P〈0．05）。使用NF-κB特异性抑制剂处理后,NCS组和IL-1β组细胞侵袭和迁移能力显著性降低（P〈0．01）;MMP-2和MMP-9的表达也显著性减少（P〈0．01）。结论坏死血管平滑肌细胞能够上调MMP-2和MMP-9的表达,促进正常细胞的侵袭和迁移,且这种促进作用与IL-1β的大量释放诱导NF-κB的活化有关。     

Distinct roles of vascular endothelial growth factor receptor-1- and receptor-2-mediated signaling in T cell priming and Th17 polarization to lipopolysaccharide-containing allergens in the lung

Vascular endothelial growth factor (VEGF) is a key mediator in the development of airway immune dysfunction to inhaled allergens. However, the exact role of its receptors-mediated signaling is controversial. In this study, we evaluated the role of VEGF receptor (VEGFR)-1- and VEGFR-2-mediated signaling in T cell priming and polarization in the context of inhalation of LPS-containing allergens. A murine asthma model of mixed Th1 and Th17 cell responses was generated using intranasal sensitization with LPS-containing allergens. Pharmacologic intervention was performed during sensitization. In vivo production of VEGF and Th1- and Th17-polarizing cytokines (IL-12p70 and IL-6, respectively) were upregulated by airway exposure to LPS. Pharmacological intervention with a VEGFR-2-neutralizing Ab (anti-Flk1 mAb) abolished the production of IL-6 (but not IL-12p70) and the subsequent development of allergen-specific Th17 cell response. On the other hand, blocking VEGFR-1 signaling with a VEGFR-1 antagonist (anti-Flt1 hexapeptide) did not affect the production of IL-12p70 and IL-6. However, blocking VEGFR-1 signaling resulted in T cell tolerance rather than priming, mainly by inhibiting the maturation of lung dendritic cells, and their migration into lung-draining lymph nodes. These results suggest that T cell priming to LPS-containing allergens depends on VEGFR-1-mediated signaling, and the subsequent Th17 polarization depends on VEGFR-2 signaling.