Platelet-activating factor stimulates interleukin-6 production by human endothelial cells and synergizes with tumor necrosis factor for enhanced production of granulocyte-macrophage colony stimulating factor

Associations between healthy food groups and platelet-activating factor, lipoprotein-associated phospholipase A2 and C-reactive protein: a cross-sectional study

PURPOSE

To investigate the association between pro-inflammatory markers platelet-activating factor (PAF), lipoprotein-associated phospholipase A2 (Lp-PLA2), hsCRP, and intake of core food groups including fruit, cruciferous and other vegetables, grains, meat and poultry, fish and seafood, nuts and legumes, and dairy.

METHODS

A cross-sectional study was conducted. 100 adults (49 ± 13 years, 31% male) with variable cardiovascular disease risk were recruited. Data were collected in 2021 and 2022. Fasting PAF, Lp-PLA2 activity, hsCRP and usual dietary intake (via a validated food frequency questionnaire) were measured. Intake of foods were converted into serves and classified into food groups. Correlations and multiple regressions were performed with adjustment for confounders.

RESULTS

A one-serve increase in cruciferous vegetables per day was associated with 20-24% lower PAF levels. An increase of one serve per day of nuts and legumes was associated with 40% lower hsCRP levels. There were small correlations with PAF and Lp-PLA2 and cheese, however, these were not significant at the Bonferroni-adjusted P < 0.005 level.

CONCLUSION

The lack of associations between PAF and Lp-PLA2 and other healthy foods may be due to confounding by COVID-19 infection and vaccination programs which prevents any firm conclusion on the relationship between PAF, Lp-PLA2 and food groups. Future research should aim to examine the relationship with these novel markers and healthy food groups in a non-pandemic setting.

Interrelationships among platelet-activating factor and lipoprotein-associated phospholipase A2 activity and traditional cardiovascular risk factors

Traditionally cardiovascular disease (CVD) risk has been assessed through blood lipids and inflammatory marker C-reactive protein (hsCRP). Recent clinical interest in novel pro-inflammatory markers platelet-activating factor (PAF) and lipoprotein-associated phospholipase A₂ (Lp-PLA₂ ) recognizes that vascular damage can exist in the absence of traditional risk factors. This cross-sectional study investigated the potential relationship between circulating PAF, Lp-PLA₂ , hsCRP, and traditional risk factors for CVD. One hundred adults (49 ± 13 years, 31% male) with variable CVD risk were recruited. Fasting inflammatory markers PAF, Lp-PLA₂ and hsCRP and total, high-density lipoprotein (HDL), low-density lipoprotein (LDL) cholesterol, and triglycerides were measured. Blood pressure, body mass index, and waist circumference were measured. Medical and physical activity data were self-reported. Linear and multiple regressions were performed. PAF, Lp-PLA₂ , and hsCRP independently correlated with several CVD risk factors. PAF was correlated significantly with risk factors in an unexpected way; there was a medium positive correlation between PAF and HDL cholesterol (r = 0.394, p < 0.001) and medium negative correlations with Total:HDL cholesterol; (r = -0.436, p < 0.001) systolic blood pressure; (r = -0.307, p = 0.001); BMI (r = -0.381, p < 0.001); and waist circumference (r = -0.404, p < 0.001). There were large positive correlations between Lp-PLA₂ and LDL (r = 0.525, p < 0.001) and non-HDL cholesterol (r = 0.508, p < 0.001). There were large positive correlations between hsCRP and Total:HDL cholesterol (r = 0.524, p < 0.001); BMI (r = 0.668, p < 0.001); and waist circumference (r = 0.676, p < 0.001). PAF, Lp-PLA₂ , and hsCRP are implicated in the pathophysiology of inflammation in CVD; however, the relationships between each marker and traditional risk factors were different suggesting they may be involved in different atherogenic pathways.

The association between dietary patterns and the novel inflammatory markers platelet-activating factor and lipoprotein-associated phospholipase A2: a systematic review

CONTEXT

Atherosclerosis is a disease of chronic inflammation. Recent research has identified 2 novel inflammatory biomarkers: platelet-activating factor (PAF) and lipoprotein-associated phospholipase A2 (Lp-PLA2). Diet has been proposed as a mediator of inflammation, but to date, the focus for these novel biomarkers has been on individual foods and nutrients rather than overall dietary patterns.

OBJECTIVE

To systematically review the literature on the association between dietary patterns and PAF and Lp-PLA2.

DATA SOURCES

The PubMed, Embase, CINAHL, and Cochrane CENTRAL literature databases were searched.

DATA ANALYSIS

Study quality was evaluated using the Quality Criteria Checklist. Sixteen studies (n = 4 observational and n = 12 interventional) were included and assessed for associations between dietary patterns and PAF and Lp-PLA2.

CONCLUSION

Study quality varied from neutral (n = 10) to positive (n = 6). Mediterranean, heart healthy, and vegetarian dietary patterns were associated with improved levels of PAF and Lp-PLA2. Conversely, Western dietary patterns were less favorable. A range of well-established, healthier dietary patterns may lower inflammation and the risk of atherosclerosis. More well-designed studies are needed to confirm these findings and identify other dietary patterns that improve inflammation.

Regulation of platelet-activating factor-mediated interleukin-6 promoter activation by the 48 kDa but not the 45 kDa isoform of protein tyrosine phosphatase non-receptor type 2

Background

An underlying state of inflammation is thought to be an important cause of cardiovascular disease. Among cells involved in the early steps of atherosclerosis, monocyte-derived dendritic cells (Mo-DCs) respond to inflammatory stimuli, including platelet-activating factor (PAF), by the induction of various cytokines, such as interleukin 6 (IL-6). PAF is a potent phospholipid mediator involved in both the onset and progression of atherosclerosis. It mediates its effects by binding to its cognate G-protein coupled receptor, PAFR. Activation of PAFR-induced signaling pathways is tightly coordinated to ensure specific cell responses.

Results

Here, we report that PAF stimulated the phosphatase activity of both the 45 and 48 kDa isoforms of the protein tyrosine phosphatase non-receptor type 2 (PTPN2). However, we found that only the 48 kDa PTPN2 isoform has a role in PAFR-induced signal transduction, leading to activation of the IL-6 promoter. In luciferase reporter assays, expression of the 48 kDa, but not the 45 kDa, PTPN2 isoform increased human IL-6 (hIL-6) promoter activity by 40% after PAF stimulation of HEK-293 cells, stably transfected with PAFR (HEK-PAFR). Our results suggest that the differential localization of the PTPN2 isoforms and the differences in PAF-induced phosphatase activation may contribute to the divergent modulation of PAF-induced IL-6 promoter activation. The involvement of PTPN2 in PAF-induced IL-6 expression was confirmed in immature Mo-DCs (iMo-DCs), using siRNAs targeting the two isoforms of PTPN2, where siRNAs against the 48 kDa PTPN2 significantly inhibited PAF-stimulated IL-6 mRNA expression. Pharmacological inhibition of several signaling pathways suggested a role for PTPN2 in early signaling events. Results obtained by Western blot confirmed that PTPN2 increased the activation of the PI3K/Akt pathway via the modulation of protein kinase D (PKD) activity. WT PKD expression counteracted the effect of PTPN2 on PAF-induced IL-6 promoter transactivation and phosphorylation of Akt. Using siRNAs targeting the individual isoforms of PTPN2, we confirmed that these pathways were also active in iMo-DCs.

Conclusion

Taken together, our data suggest that PTPN2, in an isoform-specific manner, could be involved in the positive regulation of PI3K/Akt activation, via the modulation of PKD activity, allowing for the maximal induction of PAF-stimulated IL-6 mRNA expression.

Regulation of platelet-activating factor-mediated protein tyrosine phosphatase 1B activation by a Janus kinase 2/calpain pathway

Atherosclerosis is a pro-inflammatory condition underlying many cardiovascular diseases. Platelet-activating factor (PAF) and interleukin 6 (IL-6) are actively involved in the onset and progression of atherosclerotic plaques. The involvement of monocyte-derived macrophages is well characterized in the installation of inflammatory conditions in the plaque, but less is known about the contribution of monocyte-derived dendritic cells (Mo-DCs). In the same way, the involvement of calcium, phospholipase C and A2 in PAF-induced IL-6 production, in different cells types, has been shown; however, the importance of the Jak/STAT pathway and its regulation by protein-tyrosine phosphatases in this response have not been addressed. In this study, we report that PAF stimulates PTP1B activity via Jak2, thereby modulating PAF-induced IL-6 production. Using HEK 293 cells stably transfected with the PAF receptor in order to discriminate the pathway components, our results suggest that Jak2 modulates PAF-induced IL-6 production via both positive and negative pathways. Jak2 kinase activity was necessary for maximal transactivation of the IL-6 promoter, as seen by luciferase assays, whereas the same kinase also downregulated this promoter transactivation through the activation of a calcium/calpain/PTP1B pathway. The same pathways were operational in monocyte-derived dendritic cells, since PAF-induced PTP1B activation negatively regulated PAF-induced IL-6 mRNA production and, in addition, Jak2 activated calpain, one of the components involved in PAF-induced PTP1B activation. Results obtained in this study indicate that Jak2 activation is important for maximal IL-6 promoter transactivation by PAF and that PTP1B is involved in the negative regulation of this transactivation. However, PTP1B does not directly regulate Jak2 activation, but rather Jak2 regulates PAF-induced PTP1B activation.

Feed-Forward Reciprocal Activation of PAFR and STAT3 Regulates Epithelial-Mesenchymal Transition in Non-Small Cell Lung Cancer

Platelet-activating factor receptor (PAFR), a G-protein-coupled receptor, has been implicated in tumorigenesis, but its contributions to metastatic progression have not been investigated. Here, we show that PAFR is overexpressed in non-small cell lung cancer (NSCLC) as well as in breast, colorectal, and gastric carcinomas. Expression of PAFR correlates closely with clinical stages, survival time, and distant metastasis. In human NSCLC cells, activation of the PAF/PAFR signaling axis accentuated malignant character, including by stimulating epithelial-mesenchymal transition (EMT). In contrast, silencing PAFR in aggressive NSCLC cells inhibited these effects. Mechanistic investigations showed that PAFR stimulated EMT by activating STAT3 via upregulation of G-protein-dependent SRC or JAK2 kinase activity. Notably, STAT3 transcriptionally elevated PAFR expression. Thus, activation of PAFR in NSCLC cells initiated a forward feedback loop responsible for mediating the aggressive malignant character of NSCLC cells in vitro and in vivo. Reinforcing this reciprocal activation loop, PAF/PAFR signaling also upregulated IL6 expression and thereby STAT3 activation. Overall, our results elucidated an important role for PAFR dysregulation in the pathogenicity of NSCLC and unraveled a forward feedback loop between PAFR and STAT3 that acts to drive the malignant progression of NSCLC.

pH of drinking water influences the composition of gut microbiome and type 1 diabetes incidence

Nonobese diabetic (NOD) mice spontaneously develop type 1 diabetes (T1D), progression of which is similar to that in humans, and therefore are widely used as a model for understanding the immunological basis of this disease. The incidence of T1D in NOD mice is influenced by the degree of cleanliness of the mouse colony and the gut microflora. In this report, we show that the T1D incidence and rate of disease progression are profoundly influenced by the pH of drinking water, which also affects the composition and diversity of commensal bacteria in the gut. Female NOD mice that were maintained on acidic pH water (AW) developed insulitis and hyperglycemia rapidly compared with those on neutral pH water (NW). Interestingly, forced dysbiosis by segmented filamentous bacteria (SFB)-positive fecal transfer significantly suppressed the insulitis and T1D incidence in mice that were on AW but not in those on NW. The 16S rDNA-targeted pyrosequencing revealed a significant change in the composition and diversity of gut flora when the pH of drinking water was altered. Importantly, autoantigen-specific T-cell frequencies in the periphery and proinflammatory cytokine response in the intestinal mucosa are significantly higher in AW-recipient mice compared with their NW counterparts. These observations suggest that pH of drinking water affects the composition of gut microflora, leading to an altered autoimmune response and T1D incidence in NOD mice.

Immunoregulatory protein profiles of necrotizing enterocolitis versus spontaneous intestinal perforation in preterm infants

Necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP) are the most common acute surgical emergencies associated with high morbidity and mortality in preterm infants. We aimed to compare the profiles of immunoregulatory proteins and identify novel mediators in plasma of NEC and SIP infants. We also investigated the expression of target genes in resected intestinal tissues and an enterocyte cell line. Using Cytokine Antibody Array assay, we reported the first comparative profiles of immunoregulatory proteins in plasma of NEC and SIP infants, and showed that dysregulated proteins belonged to functionally diversified categories, including pro- and anti-inflammation, angiogenesis, cell growth, wound healing, anti-apoptosis, cell adhesion and extracellular matrix reorganization. Validation by ELISA confirmed significantly higher concentrations of interleukin (IL)-6, angiopoietin (Ang)-2, soluble type II interleukin-1 receptor (sIL-1RII), and soluble urokinase-type plasminogen activator receptor (suPAR) in NEC infants compared with gestational age-matched control, and a lower level of an epidermal growth factor receptor, secreted form of receptor tyrosine-protein kinase ErbB3 (sErbB3), compared with SIP infants. mRNA expressions of IL1-RII and uPAR were up-regulated in resected bowel tissues from NEC infants, indicating that immunoregulation also occurred at the cellular level. In FHs-74 Int cells, Ang-2, IL1-RII and uPAR mRNA expressions were significantly induced by the combined treatment with lipopolysaccharide (LPS) and platelet activating factor (PAF). Our study provided plasmatic signatures of immunoregulatory proteins in NEC and SIP infants, and demonstrated involvement of multiple functional pathways. The magnitude of changes in these proteins was significantly more extensive in NEC infants, reflecting the different nature of injury and/or severity of inflammation. We speculate that dysregulation of IL-6, Ang-2, IL-1RII and uPAR occurred at both systemic and cellular levels, and probably mediated via LPS and endogeneous PAF signals. Such exaggerated immunologic responses may account for the high morbidity and mortality in NEC compared with SIP patients.

Barrier protective effects of withaferin A in HMGB1-induced inflammatory responses in both cellular and animal models

Withaferin A (WFA), an active compound from Withania somnifera, is widely researched for its anti-inflammatory, cardioactive and central nervous system effects. In this study, we first investigated the possible barrier protective effects of WFA against pro-inflammatory responses in human umbilical vein endothelial cells (HUVECs) and in mice induced by high mobility group box 1 protein (HMGB1) and the associated signaling pathways. The barrier protective activities of WFA were determined by measuring permeability, leukocytes adhesion and migration, and activation of pro-inflammatory proteins in HMGB1-activated HUVECs. We found that WFA inhibited lipopolysaccharide (LPS)-induced HMGB1 release and HMGB1-mediated barrier disruption, expression of cell adhesion molecules (CAMs) and adhesion/transendothelial migration of leukocytes to human endothelial cells. WFA also suppressed acetic acid-induced hyperpermeability and carboxymethylcellulose-induced leukocytes migration in vivo. Further studies revealed that WFA suppressed the production of interleukin 6, tumor necrosis factor-α (TNF-α) and activation of nuclear factor-κB (NF-κB) by HMGB1. Collectively, these results suggest that WFA protects vascular barrier integrity by inhibiting hyperpermeability, expression of CAMs, adhesion and migration of leukocytes, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Ecklonia cava extracts inhibit lipopolysaccharide induced inflammatory responses in human endothelial cells

Ecklonia cava (EC) is a brown alga that evidences radical scavenging, bactericidal, tyrosinase inhibitory and protease inhibitory activities. However, the antiinflammatory effects in human endothelial cells and its molecular mechanism remain poorly understood. In this study, we attempted to determine whether pretreatment with EC extracts induce a significant inhibition of antiinflammatory activities in lipopolysaccharide (LPS) induced human endothelial cells. We found that each EC extract inhibits LPS induced barrier permeability, expression of cell adhesion molecules, monocytes adhesion, and transendothelial migration to human endothelial cells. Further studies revealed that EC extracts suppress the production of tumor necrosis factor-alpha (TNF-alpha) and activation of nuclear factor-kappa B (NF-kappaB). Particularly, the antiinflammatory effects of ethyl acetate (EtOAc) and butanol (n-BuOH) extracts were better than those of other extracts. Collectively, these results suggest that EC extracts possess barrier integrity activity, inhibitory activity on cell adhesion and migration to endothelial cells by blocking the activation of NF-kappaB expression and production of TNF-alpha, thereby endorsing its usefulness as therapy for vascular inflammatory diseases.

Aspirin resistance is more common in lacunar strokes than embolic strokes and is related to stroke severity

The aim of this study was to investigate the relationship between aspirin resistance, ischaemic stroke subtype, stroke severity, and inflammatory cytokines. Aspirin resistance was assessed by thrombelastography in 45 people with ischaemic stroke and 25 controls. Plasma interleukin (IL)-6 was measured. Stroke severity was assessed using the modified Rankin scale and National Institute of Health Stroke Score within 72 h of stroke. Aspirin resistance was more common in the stroke than the control group (67% versus 40%, P=0.028), and within the stroke group the aspirin-resistant group had a higher Rankin score (4.0 versus 2.0, P=0.013). Aspirin resistance was greater in lacunar than embolic strokes (platelet activation 79% versus 59%, P=0.020). The stroke aspirin-resistant group had higher levels of IL-6 than the stroke aspirin-sensitive group (2.4+/-1 versus 1.8+/-0.9 ng/mL, P=0.037). Using multivariate analysis, we examined the interrelationships between aspirin resistance, IL-6, and stroke severity. These analyses showed that IL-6 was independently associated with stroke severity as the outcome (B=3.738, P=0.036), and aspirin resistance was independently associated with IL-6 (B=0.765, P=0.005) as the outcome. In conclusion, aspirin resistance is related to stroke severity and aspirin resistance is more common in lacunar strokes than embolic strokes.

HCl-induced inflammatory mediators in cat esophageal mucosa and inflammatory mediators in esophageal circular muscle in an in vitro model of esophagitis

Platelet-activating factor (PAF) and interleukin-6 (IL-6) are produced in the esophagus in response to HCl and affect ACh release, causing changes in esophageal motor function similar to esophagitis (Cheng L, Cao W, Fiocchi C, Behar J, Biancani P, and Harnett KM. Am J Physiol Gastrointest Liver Physiol 289: G418-G428, 2005). We therefore examined HCl-activated mechanisms for production of PAF and IL-6 in cat esophageal mucosa and circular muscle. A segment of normal mucosa was tied at both ends, forming a mucosal sac (Cheng L, Cao W, Fiocchi C, Behar J, Biancani P, and Harnett KM. Am J Physiol Gastrointest Liver Physiol 289: G860-G869, 2005) that was filled with acidic Krebs buffer (pH 5.8) or normal Krebs buffer (pH 7.0) as control and kept in oxygenated Krebs buffer for 3 h. The supernatant of the acidic sac (MS-HCl) abolished contraction of normal muscle strips in response to electric field stimulation. The inhibition was reversed by the PAF antagonist CV3988 and by IL-6 antibodies. PAF and IL-6 levels in MS-HCl and mucosa were significantly elevated over control. IL-6 levels in mucosa and supernatant were reduced by CV3988, suggesting that formation of IL-6 depends on PAF. PAF-receptor mRNA levels were not detected by RT-PCR in normal mucosa, but were significantly elevated after exposure to HCl, indicating that HCl causes production of PAF and expression of PAF receptors in esophageal mucosa and that PAF causes production of IL-6. PAF and IL-6, produced in the mucosa, are released to affect the circular muscle layer. In the circular muscle, PAF causes production of additional IL-6 that activates NADPH oxidase to induce production of H(2)O(2). H(2)O(2) causes formation of IL-1beta that may induce production of PAF in the muscle, possibly closing a self-sustaining cycle of production of inflammatory mediators.

PAF antagonist treatment reduces pro-inflammatory cytokine mRNA after spinal cord injury

Platelet-activating factor (PAF) is a pro-inflammatory molecule which contributes to secondary damage after spinal cord injury (SCI). To test if PAF contributes to cytokine induction following SCI, female Long-Evans rats were pretreated with the PAF antagonist WEB 2170 prior to receiving a contusion injury at spinal cord level T10 using the NYU impactor. RNase protection assay (RPA) analysis revealed that IL-1alpha mRNA peaked at I h post-injury while IL-1beta and IL-6 mRNA levels were higher and peaked at 6 h.TNF-alpha mRNA was almost undetectable. All mRNA levels approached baseline by 24 h. Treatment with WEB 2170 (1 mg/kg, i.p.) 15 min prior to injury significantly decreased mRNA levels for all three cytokines at 6 h post-injury, but not at I h post-injury. These results demonstrate a role for PAF in proinflammatory cytokine induction after SCI.

Anti-inflammatory effects of peripheral benzodiazepine receptor ligands in two mouse models of inflammation

In vivo treatment of mice with peripheral benzodiazepine receptor ligands exerts an inhibitory effect on the inflammatory response in two models of acute inflammation. In the first model, pretreatment of the animals (24 h) with 1-(2-chlorophenyl)-N-methyl-N(1-methylpropyl)-3-isoquinoline carboxamide (PK11195) and 7-chloro-5-(4-Chlorophenyl)-1, 3-dihydro-1-methyl-2-H-1,4-benzodiazepin-2 (Ro5-4864), at different doses (0.00001-10 mg/kg, i.p.) dose dependently inhibited the formation of mouse paw oedema induced by carrageenan with mean ID(50s) of 0.009 (95% confidence limits=0.0076-0.013) and 0.04 (95% confidence limits=0.025-0.0086) mg/kg, respectively. Both ligands (0. 1 mg/kg, i.p.) inhibited in the same way the mouse paw oedema induced by carrageenan in animals with and without adrenal glands. PK11195 and Ro5-4864 (0.1 mg/kg, i.p.) inhibited the mouse paw oedema induced by several inflammatory mediators. In the second model, the pretreatment (24 h) with peripheral benzodiazepine receptor ligands (0.1 mg/kg, i.p.) exerted an inhibitory effect on neutrophil influx and produce a marked inhibition of carrageenan-produced interleukin-13 and interleukin-6 in pleural exudation. Our results extend previous findings that peripheral benzodiazepine receptor is involved in the inflammatory response, and suggest that this action may be linked to the action of different inflammatory mediators, probably mainly by the inhibition of the release of pro-inflammatory cytokines.

Detection of Functional Platelet-Activating Factor Receptors on Human Tonsillar B Lymphocytes

Although platelet-activating factor (PAF) receptors have been found on B lymphoblastoid cell lines, the action of PAF on freshly isolated human B cells has not been clearly demonstrated. Using a sensitive semiquantitative reverse-transcriptase PCR, we have found PAF receptor mRNA expressed by tonsillar B lymphocytes, but little in T lymphocytes. Examination of Percoll-fractionated tonsillar B cells indicated that the low density (primarily germinal center cells) and medium density fractions had approximately twofold more PAF receptor mRNA relative to the high density fraction. PAF (10−7 M) stimulated increases in intracellular Ca2+ that were consistently higher in the low and medium density B lymphocytes compared with high density cells. The PAF receptor antagonist Web 2170 inhibited this. Addition of PAF, but not lyso- or enantio-PAF, induced four- to sixfold greater synthesis of IgM and IgG in low and medium density cells compared with unstimulated controls, but had little effect on Ig production by high density cells. To investigate how PAF may influence Ig synthesis, PAF-stimulated B cells were examined for production of the Th2-type cytokines IL-4 and IL-13. PAF induced IL-4 and IL-13 mRNA expression in 17% of CD20+ cells, and IL-4 was detected in cell supernatants after 48–72 h of culture. Together, these data strongly suggest that functional PAF receptors are expressed on B cells in tonsils.

Vascular Endothelial Growth Factor Inhibits the Development of Dendritic Cells and Dramatically Affects the Differentiation of Multiple Hematopoietic Lineages In Vivo

Defective function of dendritic cells (DC) in cancer has been recently described and may represent one of the mechanisms of tumor evasion from immune system control. We have previously shown in vitro that vascular endothelial growth factor (VEGF), produced by almost all tumors, is one of the tumor-derived factors responsible for the defective function of these cells. In this study, we investigated whether in vivo infusion of recombinant VEGF could reproduce the observed DC dysfunction. Continuous VEGF infusion, at rates as low as 50 ng/h (resulting in serum VEGF concentrations of 120 to 160 pg/mL), resulted in a dramatic inhibition of dendritic cell development, associated with an increase in the production of B cells and immature Gr-1+ myeloid cells. Infusion of VEGF was associated with inhibition of the activity of the transcription factor NF-κB in bone marrow progenitor cells. Experiments in vitro showed that VEGF itself, and not factors released by VEGF-activated endothelial cells, affected polypotent stem cells resulting in the observed abnormal hematopoiesis. These data suggest that VEGF, at pathologically relevant concentrations in vivo, may exert effects on pluripotent stem cells that result in blocked DC development as well as affect many other hematopoietic lineages.

Vascular Endothelial Growth Factor Inhibits the Development of Dendritic Cells and Dramatically Affects the Differentiation of Multiple Hematopoietic Lineages In Vivo

Defective function of dendritic cells (DC) in cancer has been recently described and may represent one of the mechanisms of tumor evasion from immune system control. We have previously shown in vitro that vascular endothelial growth factor (VEGF), produced by almost all tumors, is one of the tumor-derived factors responsible for the defective function of these cells. In this study, we investigated whether in vivo infusion of recombinant VEGF could reproduce the observed DC dysfunction. Continuous VEGF infusion, at rates as low as 50 ng/h (resulting in serum VEGF concentrations of 120 to 160 pg/mL), resulted in a dramatic inhibition of dendritic cell development, associated with an increase in the production of B cells and immature Gr-1+ myeloid cells. Infusion of VEGF was associated with inhibition of the activity of the transcription factor NF-κB in bone marrow progenitor cells. Experiments in vitro showed that VEGF itself, and not factors released by VEGF-activated endothelial cells, affected polypotent stem cells resulting in the observed abnormal hematopoiesis. These data suggest that VEGF, at pathologically relevant concentrations in vivo, may exert effects on pluripotent stem cells that result in blocked DC development as well as affect many other hematopoietic lineages.