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CUTTING EDGE |




* Neuroinflammation Research Center, Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195;
Division of Immunology, Infection and Inflammation, University of Glasgow, Glasgow, United Kingdom;
University of Southern California, Los Angeles, CA 90089;
Immunobiology Center, Mount Sinai School of Medicine, New York, NY 10029; and
¶ National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709
| Abstract |
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but normal IL-5. CD11c+ dendritic cells accumulated abnormally in cutaneous immunization sites of D6/ mice. Surprisingly, D6, a "silent" chemokine receptor, supports immune response generation. | Introduction |
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-arrestins for internalization. These receptors are required for the chemotactic and activating responses of leukocytes to the chemokine ligands. In addition to classical receptors, there are at least three chemokine-binding molecules that have moderate to high homology to classical receptors but lack G protein coupling motifs and are incapable of eliciting chemotactic or activating responses to a ligand (1). Two of these "silent" receptors, D6 and the Duffy Ag receptor for chemokines (DARC),3 have been characterized in some detail (1). The biological functions of DARC, which is expressed on erythrocytes and postcapillary venules, seem to be 2-fold: to transfer chemokines from parenchymal sites of synthesis across endothelial barriers and to provide a binding "sink" for chemokines in the circulation. Based on in vitro observations, D6 was proposed as a chemokine-scavenging receptor, functioning to aid in the resolution of inflammatory reactions. D6 is selectively expressed on the lymphatic endothelium. Upon transfection into lymphatic endothelial cells or human embryonic kidney cells (2, 3), D6 shuttles rapidly between plasma membrane and early endosomes independently of ligand engagement; consistent with these findings, D6 associated constitutively with
-arrestins (4). After binding its ligands, which include >12 inflammatory CC chemokines, D6 delivers these components to sites of intracellular degradation. As predicted by the scavenger receptor paradigm for D6, mice that lacked D6 exhibited markedly increased cutaneous inflammatory reactions in two distinct models (5, 6). Following phorbol ester painting, D6/ mice showed remarkably sustained persistence of its inflammatory chemokine ligands along with psoriasiform skin changes that included skin thickening, hyperkeratosis, marked inflammatory infiltrates, and angiogenesis (5). The pathology was reversed by blocking chemokine availability with neutralizing Abs or by depleting T cells or abrogating TNF signaling, indicating its inflammatory and chemokine-dependent nature. Upon s.c. challenge with CFA, the D6/ mice showed many of these features, including increased inflammatory infiltrates, but without hyperkeratosis (6). D6/ mice that received CFA showed increased amounts of CC chemokines and increased cellularity in the draining lymph nodes, suggesting an enhanced flux of chemokines across the lymphatic vessels. In this regard, chemokines are transported from local inflammatory sites to draining lymph nodes and mediate the recruitment of circulating monocytes across high endothelial venules (7). Although chemokines clearly orchestrate this "remote control" process, its physiological importance in establishing adaptive immune responses remains incompletely defined. In the current study we addressed two questions. 1) Would enhanced inflammation in the skin of D6/ mice affect the induction of experimental autoimmune encephalomyelitis (EAE) by s.c. immunization? 2) Would reduced potential clearance of chemokines from the inflamed CNS worsen the severity of EAE? Surprisingly, we found that D6/ mice were relatively resistant to the induction of EAE. These results widen the functional spectrum of nonsignaling chemokine receptors and suggest that the orchestrated delivery of chemokines to draining lymph nodes or their clearance from immunization sites may play an important role in the generation of immune responses.
| Materials and Methods |
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The generation and genotyping of D6-deficient mice has been described previously (5). D6-deficient mice had been backcrossed to C57BL/6J (B6) mice for 12 generations, and D6+/ mice were intercrossed to obtain D6+/+, D6+/, and D6/ mice. In all experiments, age- and sex-matched littermate cohorts at 810 wk of age were used. All mice were housed under pathogen-free conditions in the animal facility at the Cleveland Clinic Foundation, Cleveland, OH. All protocols for animal research met the requirements of the Animal Research Committee of the Cleveland Clinic Foundation and were in compliance with the Public Health Service policy on humane care and use of laboratory animals.
Induction and analysis of EAE
Active immunization. Induction of EAE was performed as previously described (8). Briefly, mice were s.c. injected at two sites with 100 µg of rat myelin oligodendroglial glycoprotein (MOG) peptide 3555 (MEVGWYRSPFSRVVHLYRNGK; >95% purity) (Bio-Synthesis) emulsified in CFA containing 400 µg of Mycobacterium tuberculosis (Difco Laboratories). On the same day (day 0) and on day 2 postimmunization (p.i.), mice were i.v. injected with 200 ng of pertussis toxin (Sigma-Aldrich). All mice were weighed, examined, and graded daily for neurological signs in a blinded manner as follows: 0, no disease; 1, decreased tail tone or slightly clumsy gait; 2, tail atony and moderately clumsy gait and/or poor righting ability; 3, limb weakness; 4, limb paralysis; and 5, moribund state. The day of EAE onset was calculated by adding the first day of clinical signs for individual mice and dividing by the number of mice in the group. The day of peak EAE was calculated by determining the first day of maximum EAE score for individual mice and dividing by the number of mice in the group. Mean maximum score was calculated by adding peak scores of individual mice and dividing by the number of mice. Cumulative EAE score was calculated by adding total EAE scores from onset until day 22 p.i. for individual mice and dividing by the number of mice. Active immunization with MOG3555 induced monophasic EAE in B6 mice and was followed for 22 days. Animals were euthanized if scores were worse than grade 4.
Adoptive transfer. To prepare encephalitogenic cells for adoptive transfer of EAE, mice were immunized with MOG/CFA in the same fashion as for active EAE. Spleens and lymph nodes were collected 8 days p.i., single cell suspensions were prepared, and RBCs were lysed. Cells (6 x 106 cells/ml) were cultured in RPMI 1640 medium (supplemented with 10% FBS, 2 mM L-glutamine, 1 mM sodium pyruvate, 100 IU/ml penicillin/streptomycin, and 2 x 105 M 2-ME (Invitrogen Life Technologies)) with MOG3555 (20 µg/ml) and IL-12 (30 ng/ml) (R&D Systems). Three days after initiation of culture, the cells were harvested, washed in PBS, and injected into recipient mice that were irradiated sublethally (500 rad) within 16 h before cells injection. All mice were weighed, examined, and graded daily after cell transfer (9).
T cell recall responses: proliferation and cytokine production
T cell proliferation assays and quantification of cytokine production were performed as previously described (8). For T cell proliferation, draining lymph node cells from MOG3555-immunized mice were harvested 8 days p.i., and incubated in 96-well plates (1 x 105 per well) with MOG3555 or Con A (Sigma-Aldrich) at the indicated concentration or in medium alone. During the final 16 h of a total 72 h in culture, cells were pulsed with 1µCi/well [H]thymidine (Amersham Biosciences); plates were harvested using a Tomtec harvester and analyzed with a 1450 Wallac Microbeta Trilux liquid scintillation and luminescence counter.
For quantification of cytokine production, draining lymph node cells isolated from MOG3555-immunized D6/ or D6+/+ mice were incubated (5 x 105 cells/ml) in 24-well plates with MOG3555 (20 µg/ml). After 48 h, supernatants were collected for cytokine detection. ELISA kits for IFN-
and IL-5 were obtained from R&D Systems. A standard curve was generated with each assay. All samples were measured in duplicate and diluted if necessary.
Histology and immunohistochemistry
Histological and immunohistochemical analysis of spinal cords at different stages of EAE was done as previously described (8) using rat anti-mouse CD45 mAbs at 1/2000 dilution (clone MCA 1388; Serotec) and rabbit anti-human myelin basic protein (MBP) at 1/4000 dilution (DakoCytomation). Fresh skin tissues from CFA/MOG peptide-injected mice at day 3 or day 8 p.i., both ipsilateral and contralateral to the injection site, were dissected and embedded in OCT on dry ice. Eight-micron sections were prepared and dried overnight at room temperature and stored at 80°C before using. For H&E and immunohistochemical staining, skin tissues sections were air dried for 30 min, fixed in acetone at room temperature for 10 min, rinsed in PBS, incubated with 3% hydrogen peroxide in PBS, blocked with avidin/biotin blocking kits (SP-2001; Vector Laboratories) and by incubation with 10% goat or rabbit serum at room temperature for 30 min, and then incubated at 37°C for 1 h with the following primary Abs at the dilutions indicated: hamster anti-mouse CD3 at 1/100 dilution (1452c11; R&D Systems); CD11c at 1/100 dilution (HL3; BD Pharmingen); and rat anti-mouse Gr1 at 1/500 dilution (Ly-6G; BD Pharmingen). Tissues were then incubated with the appropriate biotinylated secondary Ab, goat anti-hamster (Jackson ImmunoResearch Laboratories) or rabbit anti-rat (Vector Laboratories), at 1/500 dilution for 30 min at room temperature and then with an avidin/biotin complex kit at 1/1000 dilution (PK-6100; Vector Laboratories). Sections were washed thrice with PBST buffer (PBS with 0.2% Triton X-100) after each incubation step (except for goat serum). All Abs, as well as the avidin/biotin complex, were diluted in 1% BSA in PBST. Sections were developed with 3, 3-diaminobenzidine tetrahydrochloride (SK-4100, Vector Laboratories) with hydrogen peroxide for 5 min at room temperature. Following development with 3, 3-diaminobenzidine tetrahydrochloride, tissues were rinsed in distilled-deionized H2O, counterstained with 50% hematoxylin for 5 s, and then dehydrated and mounted. All slides were visualized by light microscopy (Leica), digitized under a x2.5, x5, or x10 objective, and captured with a 3-CCD color video camera interfaced with a MagnaFIRE image analysis system (Optronics).
RT-PCR analysis
RNA was extracted using TRIzol reagent (Invitrogen Life Technologies) according to the manufacturers instructions. Reverse transcription was performed using SuperScript first strand synthesis system for RT-PCR (12371-019; Invitrogen Life Technologies) according to the manufacturers instructions. To measure the expression of D6 using RT-PCR, the following three different pairs of primers were used (from 5' to 3'; antisense to sense): D6-1, CACTGCCTCTCACCACCGTC and GGACAGAGATGGCCAGGGATG (expected size of PCR product, 509 bp); D6-2, AGCTTTACCTGCTGAACCTGG and AAGAAGAAGATCATGGCCAAGAGTG (441 bp) (5); and D6-3, GGAAGAGACAGTAATGAGTAAGGC and GTGACAGAGAGCCTGGCCTTC (374 bp) (10). The housekeeping gene GAPDH primers GGTGGAGGTCGGAGTCAACG and CAAAGTTGTCATGGATGACC (
500 bp) were used as a positive control.
Statistical analyses
The Student t test was used for the comparisons of disease severity, day of onset, day of peak, mean maximum score, cumulative EAE score, levels of T cell proliferation, and cytokine expression in comparisons between D6+/+ and D6/ mice. A
2 test was used for the comparisons of disease incidence or mortality between D6+/+ and D6/ mice. p < 0.05 was considered significant.
| Results and Discussion |
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than cells from wild-type mice (Fig. 3C) but equal amounts of IL-5 (Fig. 3D). These findings indicated that D6/ mice were impaired in the generation of MOG-specific T cell responses. There was no evidence that the failure to generate robust type 1 cytokine production was caused by a shift to a type 2 response. It was not clear whether the suboptimal response to MOG immunization in D6/ mice was attributable to a primary T cell defect or to impaired Ag presentation. The status of D6 as a nonsignaling receptor favored the interpretation that the absence of D6 affected the microenvironment required for efficient Ag presentation rather than causing a cell-intrinsic T cell defect.
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| Acknowledgments |
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| Disclosures |
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| Footnotes |
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1 This work was supported by National Institutes of Health Grant 3RO1 NS32151 (to R.M.R.) and a Junior Faculty Award from the Nancy Davis Center Without Walls (to L.L.). ![]()
2 Address correspondence and reprint requests Dr. Richard M. Ransohoff, Neuroinflammation Research Center, Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. E-mail address: ransohr{at}ccf.org ![]()
3 Abbreviations used in this paper: DARC, Duffy Ag receptor for chemokines; DC, dendritic cell; EAE, experimental autoimmune encephalomyelitis; MBP, myelin basic protein; MOG, myelin oligodendroglial glycoprotein; p.i., post immunization. ![]()
Received for publication December 23, 2005. Accepted for publication May 1, 2006.
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-Arrestin-dependent constitutive internalization of the human chemokine decoy receptor D6. J. Biol. Chem. 279: 25590-25597.
production in CXCR3/ mice with experimental autoimmune encephalomyelitis. J. Immunol. 176: 4399-4409.
-deficient mice are resistant to experimental autoimmune encephalomyelitis. J. Exp. Med. 202: 841-851.
-chemokine receptor D6. J. Biol. Chem. 272: 12495-12504. This article has been cited by other articles:
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