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CUTTING EDGE |


* Institute for Clinical Immunology and Transfusion Medicine, Justus-Liebig University, Giessen, Germany; and
Thomas E. Starzl Transplantation Institute and Department Immunology, University of Pittsburgh, Pittsburgh, PA 15213
| Abstract |
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| Introduction |
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B-dependent activation of p53 (6). Unlike the calcineurin inhibitors CsA and FK506, SFA does not suppress IL-2 transcription (5, 6), nor does it inhibit IL-2 receptor expression (6). Taken together, these data suggest that SFA exerts immunosuppressive effects on T and B cells via a novel mode of action that partially resembles the effects of Rapa. There is increasing evidence that immunophilin-binding agents, such as Rapa, exert immunosuppressive effects at the level of the APC. We reported recently that Rapa impairs Ag uptake of murine dendritic cells (DC) (8), a finding that was subsequently confirmed in human DC (9). Moreover, it was suggested that Rapa promotes in vitro apoptosis of human DC by interfering with GM-CSF signaling (10) and suppresses in vivo DC development and function (11). DC are professional APC with a unique ability to induce and control adaptive and innate immune responses (12, 13, 14, 15). Their maturation results in transition from Ag processing to APCs and is accompanied by up-regulation of costimulatory molecules (12). DC are unsurpassed in their capacity to produce bioactive IL-12, a heterodimeric proinflammatory cytokine that regulates expansion of Th1 and NK cells, bridging innate and adaptive immunity (16).
Given the pivotal role of DC in the induction and control of immune responses, it is necessary to understand how SFA affects their function. This knowledge may provide a framework for the selection and combination of immunosuppressive agents in different clinical settings. Our results show that SFA acts rapidly on human DC to abrogate IL-12p70 production and to a lesser extent, to suppress TNF-
production, while not affecting DC differentiation, phenotypic maturation, or cell viability. Thus, in comparison to the calcineurin inhibitor CsA and the mTOR inhibitor Rapa, SFA targets DC uniquely by rapid suppression of bioactive IL-12 production.
| Materials and Methods |
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SFA, kindly provided by Novartis Pharmaceuticals (Basel, Switzerland), and Rapa and CsA, purchased from Sigma-Aldrich (Seelze, Germany), were used at the indicated concentrations and time points. Stock solutions were prepared in absolute ethanol (vehicle) and diluted on the day of the experiment with culture medium. Control DC were treated with drug vehicle.
Generation of DC
Human PBMC were isolated from buffy coats of healthy blood donors by Ficoll-Paque (Pharmacia, Freiburg, Germany) density gradient centrifugation. CD14+ monocytes were purified (>95%) using CD14 immunomagnetic microbeads (Miltenyi Biotec, Bergisch Gladbach, Germany) and 3 x 106 cells were cultured in six-well flat-bottom plates, in 3 ml of DC medium, comprising RPMI 1640, L-glutamine, penicillin/streptomycin, sodium-pyruvate, nonessential amino acids, 10% heat-inactivated FCS Gold (PAA Laboratories, Linz, Austria), 1000 IU/ml recombinant human (rh) GM-CSF (Novartis Pharmaceuticals), and 1000 IU/ml rhIL-4 (Promo Cell, Heidelberg, Germany). After 3 days, 50% supernatant was replaced with fresh cytokine-containing medium. On day 6, CD1a+ DC represented >90% of cultured cells. The studies of human blood samples were approved by the Institutional Review Board.
Isolation of peripheral blood DC
CD1c+ blood DC (purity >90%) were isolated by immunomagnetic bead sorting (AutoMACS) using the CD1c DC isolation kit (Miltenyi Biotec). Briefly, in a first step, PBMC from buffy coats of blood donors were depleted of B cells with CD19 microbeads and subsequently CD1c+ DC were positively selected after indirect labeling with biotinylated CD1c mAbs and antibiotin microbeads (17).
DC stimulation and detection of cytokine production by ELISA
DC maturation was stimulated with 100 ng/ml LPS (Sigma-Aldrich) in DC medium with cytokines. For stimulation of cytokine production, DC were incubated at 2 x 106/ml in 96-well plates in DC medium with cytokines and stimulated for 24 h with 1 µg/ml LPS (Escherichia coli 0111:B4; Sigma-Aldrich) or 100 µg/ml polyinosinic-polycytidylic acid (poly I:C; Sigma-Aldrich) plus 20 ng/ml rhIFN-
(BD PharMingen, San Diego, CA). Human IL-12p70 and TNF-
were measured using BD OptEIA ELISA sets (BD PharMingen).
In vivo experiments
SFA stock solution was diluted freshly in 2.5% polysorbate 80, 51% polyethylene glycol (PEG) 300 (Sigma-Aldrich) and 46.5% sterile water. Eight- to 12-wk-old male C57BL10 mice (Charles River Breeding Laboratories, Sulzfeld, Germany) were injected i.p. with SFA (10 mg/kg/day, 3 days) or vehicle. On day 3, mice were injected i.p. with 0.5 µg of murine IL-4 and 10 µg of LPS, dissolved in PBS with 1% FCS. Four hours later, the animals were killed, blood was taken, and plasma IL-12p70 levels were measured by ELISA (R&D Systems, Wiesbaden, Germany).
Flow cytometry
Surface phenotype of cultured cells was analyzed on a FACSCalibur flow cytometer (BD Biosciences, San Jose, CA) with the following mAbs: HLA-DR-PE (clone L343), CD40-PE (clone 5C3), CD83-PE (clone HB15e), CD86PE (clone GL1), CD14-FITC (clone M5E2), and CD1a-CY (clone HI149). All mAbs, including isotype-matched controls, were purchased from BD PharMingen. Apoptosis and necrosis were analyzed by staining of phosphatidylserine translocation with Annexin VPE in combination with the vital dye 7-AAD (BD PharMingen).
Real-time RT-PCR
The RNA of 5 x 106 cells was isolated by using the Qiagen Rneasy Mini kit (Hilden, Germany) and transcribed into cDNA using the Ready-To-Go You-Prime First-Strand Beads according to the manufacturers instructions (Amersham, Freiburg, Germany). Real-time RT-PCR was performed on an ABI-Prism 7000 PCR cycler (Applied Biosystems, Foster City, CA). The following validated PCR primers and TaqMan MGB probes (6FAM-labeled) were used: IL-12p35 (assay ID: HS00168405_m1), IL-12p40 (Hs00233688_m1), IL-23p19 (Hs00372324_m1). As endogenous controls, two independent primer sets with TaqMan probes were used: eukaryotic 18s ribosomal RNA (Hs99999901_s1) and GAPDH (Hs99999905_m1). PCR mix was prepared according to the manufacturers instructions (Assay on demand; Applied Biosystems) and thermal cycler conditions were as follows: 1 x 10 min 95°C, 4050 cycles denaturation (15 s, 95°C) and combined annealing/extension (1 min, 60°C). Relative quantification was performed by comparison of threshold cycle values of samples with serially diluted standards.
| Results and Discussion |
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Analysis of GM-CSF/IL-4-expanded human monocyte-derived DC cultured from day 2 in the presence of SFA (1001000 nM) and harvested at day 6 showed no significant effects of SFA on DC differentiation, as demonstrated by similar numbers of CD14- CD1a+ immature DC (Fig. 1A). To induce DC maturation, immature cells were stimulated with LPS. SFA did not affect the up-regulation of costimulatory molecules (CD40, CD80, CD86) or HLA-DR (Fig. 1B), nor did it affect de novo expression of CD83 (Fig. 1B). Similar results were obtained after TNF-
(1000 U/ml) stimulation of DC.
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Addition of SFA to DC cultures on day 2 suppressed 8090% of inducible IL-12p70 production after LPS stimulation (Toll-like receptor (TLR) 4 ligation) when compared with control DC (Fig. 1C). Because IL-12p70 production can be induced by many different cytokines and microbial agents, we confirmed these findings by a second mode of stimulation through TLR3 with poly I:C and IFN-
(Fig. 1C). TNF-
production was also suppressed, but to a lesser extent (Fig. 1D). To analyze whether these effects were related to apoptotic or necrotic cell death, we performed annexin V/7-AAD staining. In accordance with a recent publication suggesting that SFA can even act as an inhibitor of cell death (18), we consistently found a low incidence of DC death in SFA-treated cultures. In SFA-treated cultures, the mean incidence of apoptotic DC was 4.1 ± 1.1% (control DC 7.5 ± 1.6%, n = 3) and the mean incidence of necrotic DC was 0.9 ± 0.7% (control DC 1.6 ± 1%; n = 3).
SFA acts rapidly on already differentiated DC
To investigate whether SFA needed to be present during DC differentiation to block IL-12p70 production, we added SFA at different time points during DC generation (days 26). SFA blocked IL-12p70 production after LPS stimulation at all time points with similar potency (Fig. 2A). SFA even blocked IL-12p70 production potently when added as late as day 6, 60 min before stimulation, suggesting that it was acting rapidly on differentiated DC (IC50 108 ± 45 nm; Fig. 2B). Similar results were obtained after poly I:C/IFN-
stimulation of DC (data not shown).
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The calcineurin-inhibitor CsA has been reported by different investigators to have a moderate or no suppressive effect on IL-12 production by DC (19, 20). The mTOR inhibitor Rapa has been shown to inhibit DC IL-12 production if present for several days during DC differentiation, either in vitro or in vivo (9, 11). We next questioned whether the rapid and potent suppressive effect of SFA on bioactive IL-12 production by differentiated DC was unique in direct comparison to the immunophilin-binding immunosuppressants CsA and Rapa. Neither Rapa nor CsA was able to inhibit bioactive IL-12 production by DC significantly when added shortly before the stimulation (Fig. 2C). In direct contrast to CsA and Rapa, SFA was the only immunophilin-binding immunosuppressant that strongly inhibited IL-12p70 production of differentiated DC (Fig. 2C).
Blockade of IL-12 production by SFA is unlikely to be dependent of cyclophilin binding
Both SFA and CsA bind to cyclophilin in cells with high affinity (5), but affected bioactive IL-12 production by DC in a different manner: SFA blocked IL-12 production, whereas CsA did not inhibit IL-12 production (Fig. 2C). To assess whether suppression of IL-12 production was dependent on binding of SFA to cyclophilin, we performed competitive experiments with SFA and a molar excess of CsA. We found that SFA still blocked IL-12 production of DC even in the presence of a 20-fold molar excess of CsA indicating that the activity of SFA was independent of cyclophilin binding or at least not inhibited by CsA (Fig. 2D).
Confirmation of the suppressive effect of SFA on bioactive IL-12 with sorted peripheral blood DC from healthy donors
Given the fact that monocyte-derived DC may display functional differences in comparison to preformed in vivo-generated DC (21), we questioned whether SFA was able to block IL-12 production by freshly isolated peripheral blood DC, purified from healthy blood donors. CD1c+ (BDCA 1) is expressed on CD11c+CD123- DC and represents the major subset of myeloid DC in human blood (17, 22). We purified CD1c+ peripheral blood DC (purity >90%) from blood donors after depletion of B cells by immunomagnetic cell sorting (17). DC were treated with SFA and stimulated with either LPS or poly I:C/IFN-
. SFA-treated blood DC exhibited a striking decrease in bioactive IL-12 production, suggesting that SFA was effective on freshly isolated peripheral blood DC (Fig. 3A).
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To investigate whether SFA suppresses IL-12 production in vivo, we injected mice with SFA (10 mg/kg/day). On day 3, IL-12 production was stimulated in vivo by injection of LPS/IL-4 and plasma IL-12p70 levels were measured 4 h later. Results demonstrate that a short course of SFA blocks 70% of bioactive IL-12 production in vivo in comparison to vehicle-injected animals (Fig. 3B).
SFA blocks IL-12 expression by human DC at the transcriptional level
The calcineurin inhibitors CsA and FK506 exert potent immunosuppressive effects on the transcriptional level via inhibition of NFAT-induced cytokine gene expression (23), whereas mTOR inhibition by Rapa results in inhibition of translation initiation and cell cycle arrest (4). To investigate whether SFA inhibited IL-12 production by DC at the transcriptional or translational level, we performed real-time RT-PCR and quantified IL-12p35 and IL-12p40 mRNA expression. The results revealed a strong suppression of IL-12p35 and p40 mRNA expression, whereas expression of two independent housekeeping genes, 18s RNA and GAPDH was not affected (Fig. 4, AD). Relative quantification of IL-12p35 and p40 transcripts in relation to diluted standards indicated ≥90% inhibition in the presence of 500 nM SFA (Fig. 4F). Recently, IL-23, a novel member of the IL-12 cytokine family, has been discovered. IL-23 is a heterodimer, comprising IL-12p40 and the IL-23-specific p19 subunit (24). Because IL-23 is produced by DC and is suggested to play a unique role in the activation of memory T cells, as well as in autoimmune inflammation of the brain, we decided to analyze p19 mRNA in SFA-treated DC (24, 25). Short-term pretreatment of DC with SFA (1 h) blocked 84% of p19 transcription (Fig. 4, E and F).
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| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Holger Hackstein, Institute for Clinical Immunology and Transfusion Medicine, Justus-Liebig University, Giessen, Langhansstrasse 7, Giessen, D-35390 Giessen, Germany. E-mail address: Holger.Hackstein{at}immunologie.med.uni-giessen.de ![]()
3 Abbreviations used in this paper: CsA, cyclosporin A; Rapa, rapamycin; mTOR, mammalian target of Rapa; SFA, Sanglifehrin A; DC, dendritic cell; rh, recombinant human; TLR, Toll-like receptor. ![]()
Received for publication March 31, 2003. Accepted for publication May 27, 2003.
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B-dependent activation of p53. J. Biol. Chem. 276:43534.This article has been cited by other articles:
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Q. Li, A. C. Grover, E. J. Donald, A. Carr, J. Yu, J. Whitfield, M. Nelson, N. Takeshita, and A. E. Chang Simultaneous Targeting of CD3 on T Cells and CD40 on B or Dendritic Cells Augments the Antitumor Reactivity of Tumor-Primed Lymph Node Cells J. Immunol., August 1, 2005; 175(3): 1424 - 1432. [Abstract] [Full Text] [PDF] |
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J. Kallen, R. Sedrani, G. Zenke, and J. Wagner Structure of Human Cyclophilin A in Complex with the Novel Immunosuppressant Sanglifehrin A at 1.6 A Resolution J. Biol. Chem., June 10, 2005; 280(23): 21965 - 21971. [Abstract] [Full Text] [PDF] |
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A. De Creus, M. Abe, A. H. Lau, H. Hackstein, G. Raimondi, and A. W. Thomson Low TLR4 Expression by Liver Dendritic Cells Correlates with Reduced Capacity to Activate Allogeneic T Cells in Response to Endotoxin J. Immunol., February 15, 2005; 174(4): 2037 - 2045. [Abstract] [Full Text] [PDF] |
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A. M. Woltman, N. Schlagwein, S. W. van der Kooij, and C. van Kooten The Novel Cyclophilin-Binding Drug Sanglifehrin A Specifically Affects Antigen Uptake Receptor Expression and Endocytic Capacity of Human Dendritic Cells J. Immunol., May 15, 2004; 172(10): 6482 - 6489. [Abstract] [Full Text] [PDF] |
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A. Allen, Y. Zheng, L. Gardner, M. Safford, M. R. Horton, and J. D. Powell The Novel Cyclophilin Binding Compound, Sanglifehrin A, Disassociates G1 Cell Cycle Arrest from Tolerance Induction J. Immunol., April 15, 2004; 172(8): 4797 - 4803. [Abstract] [Full Text] [PDF] |
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