VPAC1 receptor expression in peripheral blood mononuclear cells in a human endotoxemia model
© Storka et al.; licensee BioMed Central Ltd. 2013
Received: 16 October 2012
Accepted: 29 April 2013
Published: 7 May 2013
Vasoactive intestinal peptide (VIP) exerts immune-modulatory actions mainly via VPAC1 receptor stimulation. VPAC1 may be a treatment target of inflammatory diseases, but little is known about the receptor expression profile in immune-competent cells in vivo.
Material and methods
20 male healthy subjects received a single intravenous bolus of 2ng/kg body weight Escherichia coli endotoxin (LPS). Receptor status was evaluated in peripherial blood cells before and 3, 6 and 24 h after LPS by FACS analysis and q-PCR. VIP plasma concentrations were measured by ELISA.
Granulocytes accounted for 51% of leukocytes at baseline and 58 ± 37% were positive for VPAC1. The granulocyte population increased 2.6 fold after LPS, and a transient down-regulation of VPAC1 to 28 ± 23% was noted at 3 h (p < 0.001), which returned to baseline at 24 hours. Baseline VPAC1 expression was low in lymphocytes (6.3 ± 3.2%) and monocytes (11 ± 9.6%). In these cells, LPS up-regulated VPAC1 at 6 h (13.2 ± 4.9%, p < 0.001) and 24 h (31.6 ± 20.5%, p = 0.001), respectively. Consistent changes were noted for the VIP-receptors VPAC2 and PAC1. VPAC1, VPAC2 and PAC1 mRNA levels were unchanged in peripheral blood mononuclear cells (PBMC). VIP plasma concentration increased from 0.5 ± 0.3 ng/ml to 0.7 ± 0.4 ng/ml at 6 h after LPS (p < 0.05) and returned to baseline within 24 h.
The time profile of VPAC receptor expression differs in granulocytes, monocytes and lymphocytes after LPS challenge in humans. Changes in circulating VIP concentrations may reflect innate immune responses.
Vasoactive intestinal peptide (VIP) has a broad range of biological actions such as dilatation of smooth muscle cells including broncho- and vasodilation, insulin releasing properties, influence on intestinal motility, and neuroprotective capacities [1–8]. VIP is also known as a potent immunomodulator [9–11]. Down-regulation of tumor necrosis factor α (TNFα) , IL-6 , IL-8, IL-12 , inducible nitric oxide synthase (i-NOS) , and enhanced production of anti-inflammatory cytokines such as IL-10 and IL-1RN  have all been described to contribute to the direct anti-inflammatory action of VIP.
These functions are mediated via three different G-protein coupled receptors, VPAC1, VPAC2 and PAC1, which are localized on immune-competent cells and on other mesenchymal and endothelial tissues in humans [17–20]. For the anti-inflammatory signaling, VPAC1 has been identified as the most important receptor .
Since VIP and VPAC-1 receptor agonists appear to affect synthesis and release of multiple cytokines, they might provide an efficient therapeutic alternative to the use of specific cytokine antibodies or antagonists as immune modulatory agents. Previous reports showed that administration of VIP attenuates the deleterious consequences of septic shock and has been successfully used in various animal models of rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease [22–26]. However, studies characterizing the expression of VPAC1 receptors on immune-competent cells and their regulation following immunological stimulation in humans are not available.
This study has therefore addressed VPAC receptor expression profiles in peripheral venous blood following systemic LPS administration in healthy human subjects. Small doses of intravenously administered LPS cause an acute inflammatory response, qualitatively similar to that occurring during the early stages of sepsis. Transient changes in systemic hemodynamics, endothelial function, permeability, pulmonary gas exchange and ventricular function can be induced within 3 hours of intravenous administration of LPS to healthy subjects. The results of this study may help to clarify to which extend the VIP receptors are involved in the systemic inflammatory response in humans.
Material and methods
The study was approved by the Ethics Committee of the Medical University Vienna (EK 725/2007) and conforms to the principles outlined in the Declaration of Helsinki, including current revisions and the Good Clinical Practice guidelines. 20 healthy male subjects aged from 18 to 45 years were included. Following a complete health examination, including physical examination, electrocardiogram, and laboratory screening subjects received intravenously 2 ng/kg body weight of E. coli endotoxin (U.S. Standard Reference Endotoxin; NIH-CC, Bethesda, MD) lipopoysaccharide (LPS) within a period of 3 minutes to induce a systemic inflammatory response. Venous blood samples were collected at baseline, 3 hours, 6 hours and 24 hours after LPS administration for peripheral blood mononuclear cells (PBMC) isolation and VIP serum level quantification. For technical reasons white blood cell count was only available from 10 subjects.
Receptor expression in peripheral venous blood
To examine the expression of VPAC1, VPAC2 and PAC1 on different blood cells, FACS analysis was performed from whole blood. As primary antibodies monoclonal mouse anti VPAC1, mouse anti VPAC2 and mouse anti PAC1 antibodies (abcam Antibody Solutions, Cambridge, UK) were used at 1:200 dilution. Following an incubation period of 20 min at 4°C blood cells were washed with FACS buffer (phosphate buffered saline supplemented with 8 mM EDTA, 0.2% bovine serum albumin and 7.6 mM sodium azide). The secondary antibody (FITC labeled goat anti mouse antibody, Bethyl, Montgomery TX, USA) was allowed to incubate for 20 min at 4°C. The different cell populations were distinguished in the forward and side scatter and confirmed by double staining for monocytes or lymphocytes, respectively (Online Annex Additional file 1: Figure S2, Additional file 2: Figure S3, Additional file 3: Figure S4). Monocytes were detected using an anti-CD14 antibody (CD14-RPE, DAKO, Glostrup, Denmark) and lymphocytes with an anti-CD3 antibody (CD3-PE, Becton Dickinson, San Diego CA, USA). Control stainings were performed with isotype-matched antibodies. Following antibody incubation the cells were washed using FACS buffer and erythrocytes were lysed in 1.55 M NH4Cl, 100 mM KHCO3 and 1 mM EDTA. As negative control, MOLT-4cells (ATCC, Middlesex, UK) which are known not to express VPAC-1, were used.
Acquisitation was performed on a Becton Dickinson FACScan flow cytometer (Becton Dickinson, San Diego CA USA) by analysing 100.000 to 300.000 events per sample.
VIP plasma concentration
After blood collection in EDTA buffered tubes, 50 μl Trasylol (Bayer Health Care Pharmaceuticals, Barmen, Germany) was added and centrifuged at 2000 g for 10 minutes at 4°C immediately to avoid degradation. EDTA plasma was frozen at -80°C. Peptides were extracted from the plasma using C-18 sept colums (containing 200 mg of C18), Buffer A and Buffer B according the protocol (Phoenix Pharmaceuticals Inc., Karlsruhe, Germany) and VIP levels measured using a commercial available enzyme linked immunoassay (Phoenix Pharmaceuticals Inc., Karlsruhe, Germany) following the manufacturer´s protocol within 1 month after sample collection. The enzyme linked immunoassay quantifies concentrations between 0.12-25 ng/ml.
VIP receptor mRNA in PBMC
Venous peripheral blood mononuclear cells (PBMC) were harvested using Ficoll density gradient centrifugation. Ficoll-Paque plus (GE Healthcare Life Sciences, Chalfont St Giles, GB) was overlayed with 5 ml EDTA blood and centrifuged for 20 minutes at 500 g at room temperature. Cells were then collected, washed twice with phosphate buffered saline (PBS) and harvested for PCR analysis.
Total RNA was isolated from PBMC using the Trizol reagent (Invitrogen, California US) according to the manufacturer’s instruction. Integrity of RNA was verified by gel electrophoresis. An aliquot of 2 μg RNA was reverse transcribed into first strand cDNA with RevertAid™ First Strand cDNA Synthesis Kit (Fermentas, Massachusetts, USA) using random hexamer primer in compliance with the standard protocol for PCR amplification. qPCR was carried out using TaqMan® Gene Expression Master Mix (Applied Biosystems, California, USA), TaqMan® Gene Expression Assays (Applied Biosystems, California US) and 1ng cDNA in a 20 μl reaction mixture. The PCR was performed on the 7500 Fast Real-Time PCR System (Applied Biosystems, California USA) under following conditions: an initial incubation at 50°C for 20 s and 95°C for 10 min followed by 40 cycles of 95°C for 15 s, 54°C for 1 min.
Threshold cycle-values (Ct) for the VPAC1 (NM_001251882.1, NM_001251883.1, NM_001251884.1, NM_001251885.1, NM_004624.3), VPAC2 (NM_003382.4) and PAC1 (NM_001099733.1, NM_001117.3) genes and the B2M housekeeping gene were determined in triplicates. Relative quantification of RNA was calculated by ΔΔ Ct method. Omission of cDNA was used as negative control.
Datasets were described using descriptive statistics as means ± SD. Data distribution was skewed and non-parametric tests were performed accordingly using SPSS® software (IBM, NY, USA). After assessing Friedman-ANOVA analysis the Wilcoxon matched-pairs test was used to compare groups. A p-value of 0.05 was considered statistically significant.
Mean blood pressure (mmHg)
Body temperature (°C)
97 ± 9
73 ± 10
36.1 ± 0.4
LPS 3 hours
92 ± 10*
87 ± 11*
37.1 ± 0.5*
LPS 6 hours
93 ± 10*
86 ± 9*
36.9 ± 0.4*
White blood cell count
Total WBC (G/l)
7.3 ± 1.4
3.9 ± 1.0
0.7 ± 0.2
2.4 ± 0.5
LPS 3 hours
9.8 ± 2.7*
9.0 ± 2.5*
0.1 ± 0.0*
0.6 ± 0.2*
LPS 6 hours
11.2 ± 1.4*
9.9 ± 1.1*
0.5 ± 0.2*
0.6 ± 0.2*
LPS 24 hours
6.4 ± 1.1
3.5 ± 0.8
0.6 ± 0.1
1.9 ± 0.4
VPAC1 receptor expression
Mean fluorescence intensity of VPAC1, VPAC2 and PAC1
A - VPAC1
30.5 ± 16.5
19.9 ± 11.7
29.6 ± 11.7
LPS 3 hours
24.3 ± 9.3 *
19.9 ± 20.4
34.1 ± 19.0
LPS 6 hours
21.4 ± 9.9 *
15.3 ± 9 *
32.5 ± 17.3
LPS 24 hours
28.5 ± 16.1
18.2 ± 7.3
31.4 ± 23.7
B - VPAC2
19.9 ± 5.7
17.4 ± 7.6
23.5 ± 10.9
LPS 3 hours
17.4 ± 7.5
13.6 ± 6.3 *
20.7 ± 10.8
LPS 6 hours
35.7 ± 86.6 *
16.0 ± 9.2
32.4 ± 41.1
LPS 24 hours
18.3 ± 7.9
19.1 ± 12.7
21.1 ± 8.5 *
C - PAC1
17.4 ± 6.2
14.8 ± 5.3
21.6 ± 10.2
LPS 3 hours
16.7 ± 8.6
12.5 ± 10.3
15.7 ± 10.2
LPS 6 hours
21.8 ± 28.1
12.5 ± 9.6 *
17.6 ± 7.2
LPS 24 hours
17.4 ± 6.0
15.4 ± 5.8
15.7 ± 6.2
The VPAC-1 expression profile was different in monocytes (Figure 1B). At baseline 11.3 ± 9.6% of monocytes were positive for VPAC1. LPS initially decreased and subsequently increased receptor expression to 7.8 ± 3.2% after 6 hours and to 31.6 ± 20.5% after 24 hours. This pattern was also detectable for MFI values (Table 3).
In lymphocytes VPAC-1 receptor expression at baseline was 6.3 ± 3.2% (Figure 1C). LPS increased receptor expression to 8.7 ± 5.9% after 3 hours and to 13.2 ± 4.9% after 6 hours. MFI values were not significantly altered in lymphocytes after LPS (Table 3).
VPAC1 mRNA expression
VPAC1 mRNA expression in PBMC was not changed after LPS administration (data not shown).
VIP plasma levels
VIP plasma concentrations were 0.5 ± 0.3 ng/ml at baseline and increased to 0.6 ± 0.3ng/ml 3 hours and to 0.7 ± 0.4 ng/ml 6 hours after LPS (p < 0.05 versus baseline). 24 hours after LPS VIP plasma concentration was 0.5 ± 0.2 ng/ml.
VPAC2 and PAC1 receptor and mRNA expression
Expression of VPAC2 receptors was substantially lower than that of VPAC1 in all three cell populations under study. A maximum of 5% of monocytes or lymphocytes stained positive for VPAC2 (Figure 1B,1C). Likewise, MFI values were lower compared to VPAC1.
After LPS administration the regulation pattern was consistent with that of VPAC1, with a downregulation of VPAC2 and PAC1 in granulocytes and an upregulation in monocytes and lymphocytes, respectively (Figure 1). Corresponding changes of MFI values were again detectable (Table 3). mRNA VPAC2 and PAC1 receptor expression was at the limit of quantification in PBMC and not altered by LPS.
The understanding of VPAC 1 receptor expression on immune-competent cells is a crucial step towards the development of VPAC agonists in human disease. This study demonstrates that in response to systemic low doses of LPS to healthy humans VPAC 1 receptor expression show a dynamic response in granulocytes, monocytes and lymphocytes. This LPS mediated effect is accompanied by a significant increase in VIP plasma concentrations.
The expression pattern of VPAC1 receptors is heterogeneous across different leukocyte populations. About 60% of granulocytes express VPAC1 under resting conditions, suggesting that these cells are particularly sensitive to alterations in VIP levels. Following LPS exposure granulocytes rapidly decrease the VPAC1 receptor density on their surface by approximately 50% within 3 hours. It is likely that receptor internalization as described by Langlet et al.,  is responsible for this decrease in VPAC1 expression.
Granulocytes are recruited to infection sites and are of importance in the early microbial clearance [28, 29]. This accumulation results in organ damage if unopposed pro-inflammatory signaling persists . Thus, the ability to down-regulate leukocyte receptor activation after clearing the offending agent seems to be as essential as cell recruitment per se to prevent excessive tissue injury. The pattern of VPAC1 expression in granulocytes may therefore represent a regulator mechanism for granulocyte cell function.
The VPAC1 receptor expression profile was not consistent across leukocyte subtypes. Given that leukocyte count was significantly increased by LPS, the absolute reduction in monocyte and lymphocyte count indicates that their VPAC1 receptor - mediated effects presumably contribute to the net action of VIP to a small extent only. In the healthy subjects under study, baseline VPAC1 expression on monocytes and lymphocytes was low but increased following LPS by 2-3 – fold. Similar results have been shown in macrophages when stimulated with LPS in vitro . Nevertheless, the upregulation detected in these cells may indicate a refinement in the immunological response to increased VIP concentrations.
The lack of changes in receptor mRNA in PBMC following LPS argues against a relevant receptor de novo synthesis in these cells. However, assessment of protein translation may not be indicative of receptor involvement in the immunomodulatory VIP-signalling since receptors are internalized after binding of their ligand VIP on the cell surface . As suggested previoulsy , recycling and re-organization of receptors on the cellular surface may be responsible for the observed short-term effect of LPS in leukocytes.
Receptor stimulation is important for the pharmacodynamic action of VIP. In our model of endotoxemia we found a transient increase in VIP plasma concentrations. This is consistent with findings in septic patients, where an acute initial increase in VIP serum levels has been reported . In contrast, decreased VIP serum levels have been described in patients with chronic pulmonary hypertension, where VPAC2 receptors are up-regulated in the pulmonary vasculature . Thus, interpretation of altered VIP serum concentration remains speculative when the receptor expression is unknown.
The factors which influence VIP receptor expression are largely unclear. The present study demonstrates that VPAC1, VPAC2 and PAC1 expression is regulated in leukocytes following systemic stimulation with LPS in vivo. In contrast to Lara-Martinez et al, VPAC2 was expressed on monocytes . However, VPAC1 is the predominant receptor in leukocytes. This is consistent with in vitro experiments where LPS is a powerful trigger for VPAC1 receptor regulation . Animal studies have demonstrated that selective activation of VPAC1 is more effective in controlling the immunological answer than VPAC2 agonists . The dynamic receptor regulation pattern observed in this study also favours VPAC1 as principal mediator of the anti-inflammatory action of VIP. Thus selective activation of VPAC1 may represent an efficacious clinical target to elicit anti-inflammatory actions without undesired side effects of simultaneous VPAC2 activation such as vasodilatation.
The present experiments were conducted employing E. coli endotoxin. It is possible that VPAC1 receptor regulation is variably sensitive to challenging agents from different bacteria, as previously described for cytokines such as TNF-α, INFγ or IL-10 . The rapid serum-clearance of LPS indicates that secondary mediators may be involved in the delayed regulation of VPAC1 in PBC . However, systemic LPS administration is more likely to activate immune-competent cells indirectly via systemic pro-inflammatory immunological mechanisms. The anti- inflammatory effect of VPAC1 agonists in clinical trials will therefore be influenced by the timing of administration and the type of infection and associated mechanisms of the innate immune system.
In summary our data support the concept that VPAC-1 is a promising immunomodulatory target receptor in humans.
This project was supported and funded by “Medical Scientific Fund of the Mayor of the City of Vienna” (Project Number 09055).
- Said SI, Mutt V: Polypeptide with broad biological activity: isolation from small intestine. Science. 1970, 169 (951): 1217-1218. 10.1126/science.169.3951.1217.View ArticlePubMedGoogle Scholar
- Mutt V, Said SI: Structure of the porcine vasoactive intestinal octacosapeptide. The amino-acid sequence. Use of kallikrein in its determination. Eur J Biochem. 1974, 42 (2): 581-589. 10.1111/j.1432-1033.1974.tb03373.x.View ArticlePubMedGoogle Scholar
- Morice A, Unwin RJ, Sever PS: Vasoactive intestinal peptide causes bronchodilatation and protects against histamine-induced bronchoconstriction in asthmatic subjects. Lancet. 1983, 2 (8361): 1225-1227.View ArticlePubMedGoogle Scholar
- Huang M, Shirahase H, Rorstad OP: Comparative study of vascular relaxation and receptor binding by PACAP and VIP. Peptides. 1993, 14 (4): 755-762. 10.1016/0196-9781(93)90109-T.View ArticlePubMedGoogle Scholar
- Offen D: Vasoactive intestinal peptide (VIP) prevents neurotoxicity in neuronal cultures: relevance to neuroprotection in Parkinson's disease. Brain Res. 2000, 854 (1–2): 257-262.View ArticlePubMedGoogle Scholar
- Brenneman DE: Identity of neurotrophic molecules released from astroglia by vasoactive intestinal peptide. Ann N Y Acad Sci. 1997, 814: 167-173. 10.1111/j.1749-6632.1997.tb46155.x.View ArticlePubMedGoogle Scholar
- Edwards AV, Bloom SR, Ghatei MA: Pancreatic endocrine responses to the peptides VIP and PACAP in the conscious calf. Exp Physiol. 1997, 82 (4): 717-727.View ArticlePubMedGoogle Scholar
- Kawai K: Pituitary adenylate cyclase activating polypeptide stimulates insulin release from the isolated perfused rat pancreas. Life Sci. 1992, 50 (4): 257-261. 10.1016/0024-3205(92)90332-J.View ArticlePubMedGoogle Scholar
- Delgado M: VIP and PACAP induce shift to a Th2 response by upregulating B7.2 expression. Ann N Y Acad Sci. 2000, 921: 68-78.View ArticlePubMedGoogle Scholar
- Gomariz R: Anti-inflammatory actions of VIP/PACAP. Role in endotoxemia. Ann N Y Acad Sci. 2000, 921: 284-288.View ArticlePubMedGoogle Scholar
- Leceta J: Receptors and transcriptional factors involved in the anti-inflammatory activity of VIP and PACAP. Ann N Y Acad Sci. 2000, 921: 92-102.View ArticlePubMedGoogle Scholar
- Delgado M: Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit endotoxin-induced TNF-alpha production by macrophages: in vitro and in vivo studies. J Immunol. 1999, 162 (4): 2358-2367.PubMedGoogle Scholar
- Martinez C: Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide modulate endotoxin-induced IL-6 production by murine peritoneal macrophages. J Leukoc Biol. 1998, 63 (5): 591-601.PubMedGoogle Scholar
- Delgado M: VIP and PACAP inhibit IL-12 production in LPS-stimulated macrophages. Subsequent effect on IFNgamma synthesis by T cells. J Neuroimmunol. 1999, 96 (2): 167-181. 10.1016/S0165-5728(99)00023-5.View ArticlePubMedGoogle Scholar
- Delgado M: Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide prevent inducible nitric oxide synthase transcription in macrophages by inhibiting NF-kappa B and IFN regulatory factor 1 activation. J Immunol. 1999, 162 (8): 4685-4696.PubMedGoogle Scholar
- Delgado M: Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide enhance IL-10 production by murine macrophages: in vitro and in vivo studies. J Immunol. 1999, 162 (3): 1707-1716.PubMedGoogle Scholar
- Sreedharan SP: Cloning and functional expression of a human neuroendocrine vasoactive intestinal peptide receptor. Biochem Biophys Res Commun. 1993, 193 (2): 546-553. 10.1006/bbrc.1993.1658.View ArticlePubMedGoogle Scholar
- Lutz EM: The VIP2 receptor: molecular characterisation of a cDNA encoding a novel receptor for vasoactive intestinal peptide. FEBS Lett. 1993, 334 (1): 3-8. 10.1016/0014-5793(93)81668-P.View ArticlePubMedGoogle Scholar
- Svoboda M: Molecular cloning and functional characterization of a human VIP receptor from SUP-T1 lymphoblasts. Biochem Biophys Res Commun. 1994, 205 (3): 1617-1624. 10.1006/bbrc.1994.2852.View ArticlePubMedGoogle Scholar
- Ogi K: Molecular cloning and functional expression of a cDNA encoding a human pituitary adenylate cyclase activating polypeptide receptor. Biochem Biophys Res Commun. 1993, 196 (3): 1511-1521. 10.1006/bbrc.1993.2423.View ArticlePubMedGoogle Scholar
- Delgado M: Anti-inflammatory properties of the type 1 and type 2 vasoactive intestinal peptide receptors: role in lethal endotoxic shock. Eur J Immunol. 2000, 30 (11): 3236-3246. 10.1002/1521-4141(200011)30:11<3236::AID-IMMU3236>3.0.CO;2-L.View ArticlePubMedGoogle Scholar
- Chorny A, Delgado M: Neuropeptides rescue mice from lethal sepsis by down-regulating secretion of the late-acting inflammatory mediator high mobility group box 1. Am J Pathol. 2008, 172 (5): 1297-1307. 10.2353/ajpath.2008.070969.PubMed CentralView ArticlePubMedGoogle Scholar
- Tuncel N, Tore FC: The effect of vasoactive intestinal peptide (VIP) and inhibition of nitric oxide synthase on survival rate in rats exposed to endotoxin shock. Ann N Y Acad Sci. 1998, 865: 586-589. 10.1111/j.1749-6632.1998.tb11241.x.View ArticlePubMedGoogle Scholar
- Delgado M: Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activation polypeptide (PACAP) protect mice from lethal endotoxemia through the inhibition of TNF-alpha and IL-6. J Immunol. 1999, 162 (2): 1200-1205.PubMedGoogle Scholar
- Cobo M: Mesenchymal stem cells expressing vasoactive intestinal peptide ameliorate symptoms in a model of chronic multiple sclerosis. Cell Transplant. 2012, Epub ahead of printGoogle Scholar
- Delgado M: Vasoactive intestinal peptide prevents experimental arthritis by downregulating both autoimmune and inflammatory components of the disease. Nat Med. 2001, 7 (5): 563-568. 10.1038/87887.View ArticlePubMedGoogle Scholar
- Langlet C: Contribution of the carboxyl terminus of the VPAC1 receptor to agonist-induced receptor phosphorylation, internalization, and recycling. J Biol Chem. 2005, 280 (30): 28034-28043. 10.1074/jbc.M500449200.View ArticlePubMedGoogle Scholar
- Baggiolini M: Activation of neutrophil leukocytes: chemoattractant receptors and respiratory burst. FASEB J. 1993, 7 (11): 1004-1010.PubMedGoogle Scholar
- Crane MJ, Hokeness-Antonelli KL, Salazar-Mather TP: Regulation of inflammatory monocyte/macrophage recruitment from the bone marrow during murine cytomegalovirus infection: role for type I interferons in localized induction of CCR2 ligands. J Immunol. 2009, 183 (4): 2810-2817. 10.4049/jimmunol.0900205.PubMed CentralView ArticlePubMedGoogle Scholar
- Teng L: Matrix metalloproteinase-9 as new biomarkers of severity in multiple organ dysfunction syndrome caused by trauma and infection. Mol Cell Biochem. 2012, 360 (1-2): 271-277. 10.1007/s11010-011-1066-0.View ArticlePubMedGoogle Scholar
- Burian B: Vasoactive intestinal peptide (VIP) receptor expression in monocyte-derived macrophages from COPD patients. Peptides. 2010, 31 (4): 603-608. 10.1016/j.peptides.2009.12.014.View ArticlePubMedGoogle Scholar
- Ortner A: VPAC receptor mediated tumor cell targeting by protamine based nanoparticles. J Drug Target. 2010, 18 (6): 457-467. 10.3109/10611860903508796.View ArticlePubMedGoogle Scholar
- Brandtzaeg P: Elevated VIP and endotoxin plasma levels in human gram-negative septic shock. Regul Pept. 1989, 24 (1): 37-44. 10.1016/0167-0115(89)90209-7.View ArticlePubMedGoogle Scholar
- Petkov V: Vasoactive intestinal peptide as a new drug for treatment of primary pulmonary hypertension. J Clin Invest. 2003, 111 (9): 1339-1346.PubMed CentralView ArticlePubMedGoogle Scholar
- Lara-Marquez M: Selective gene expression and activation-dependent regulation of vasoactive intestinal peptide receptor type 1 and type 2 in human T cells. J Immunol. 2001, 166 (4): 2522-2530.View ArticlePubMedGoogle Scholar
- Finney SJ: Differences in lipopolysaccharide- and lipoteichoic acid-induced cytokine/chemokine expression. Intensive Care Med. 2012, 38 (2): 324-332. 10.1007/s00134-011-2444-5.PubMed CentralView ArticlePubMedGoogle Scholar
- Munford RS, Andersen JM, Dietschy JM: Sites of tissue binding and uptake in vivo of bacterial lipopolysaccharide-high density lipoprotein complexes: studies in the rat and squirrel monkey. J Clin Invest. 1981, 68 (6): 1503-1513. 10.1172/JCI110404.PubMed CentralView ArticlePubMedGoogle Scholar
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