|
|
||||||||


* Department of Microbiology-Immunology and the Interdepartmental Immunobiology Center, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611; and
Miltenyi Biotec, Bergisch Gladbach, Germany
| Abstract |
|---|
|
|
|---|
production. Moreover, CNS pDCs suppressed CNS myeloid dendritic cell-driven production of IL-17, IFN-
, and IL-10 in an IDO-independent manner. The data demonstrate that pDCs play a critical regulatory role in negatively regulating pathogenic CNS CD4+ T cell responses, highlighting a new role for pDCs in inflammatory autoimmune disease. | Introduction |
|---|
|
|
|---|
and TNF (by Th1) and IL-17 (by Th17) in the CNS (2, 3). Disease progression in relapsing EAE (R-EAE) is characterized by "epitope spreading," where new T cell responses to myelin epitopes distinct from the priming epitope develop (4). Our recent evidence indicates that peripherally derived myeloid dendritic cells (mDCs) prime naive CD4+ T cells in the CNS, inducing a Th17 dominant phenotype (5, 6). In contrast, CNS plasmacytoid dendritic cells (pDCs) are inefficient at inducing the proliferation of and cytokine production by naive and activated myelin-specific CD4+ T cells, although the pDCs can ingest myelin proteins (6).
Enhanced numbers of activated pDCs have been described in MS, and activated pDCs are associated with Sjögrens syndrome, lupus, and psoriasis (7, 8, 9, 10, 11). It was therefore important to understand the role of pDCs in MS/EAE pathogenesis. Using a mAb (anti-mPCDA-1) to deplete pDCs from the CNS following R-EAE induction, we show that pDC depletion caused the rapid exacerbation of EAE severity in both the primary acute and relapse phases. Mechanistically, pDC depletion did not affect the frequency of myelin-specific CD4+ T cells in peripheral lymphoid organs but markedly enhanced CNS CD4+ T cell activation as well as IL-17 and IFN-
production. Moreover, CNS pDCs suppressed CNS mDC-driven production of IL-17, IFN-
, and IL-10 in an IDO-independent manner.
| Materials and Methods |
|---|
|
|
|---|
Female SJL/J mice were purchased from Harlan Sprague Dawley (SJL/JCrHsd) or Taconic Farms (SJL/JCrNtac). Mice were housed and cared for according to Northwestern University (Chicago, IL) Institutional Animal Care and Use Committee-approved protocols.
Induction of EAE
As previously reported using 50 µg of proteolipid protein peptide 139–151 (PLP139–151) (6).
Peptides and antibodies
PLP139–151 (HSLGKWLGHPDKF) was synthesized to >95% purity by Genemed Synthesis. Conjugated Abs were purchased from BD Pharmingen or eBioscience.
Depletion of pDCs
Mice received i.p. injections of 250 µg of anti-mouse plasmacytoid dendritic cell antigen-1 (anti-mPDCA-1) (clone JF05-1C2, rat IgG2b; Miltenyi Biotec) or purified rat IgG2b (eBioscience) every other day for four treatments.
Isolation of cells from secondary lymphoid tissues and CNS
As previously reported (6).
Flow cytometric analysis and gating
For analysis of cytokines, CNS cells were cultured for 4 h in R10 medium (6) plus GolgiStop (BD Biosciences) according to the manufacturers recommendations. Cells were stained with five- or six-color Ab mixtures. Amine-reactive, fixable, live/dead viability dye was used according to the manufacturers instructions (Molecular Probes/Invitrogen) and dead cells were excluded. Data were acquired on an BD LSR II cytometer (BD Biosciences) and analyzed using FACSDiva (BD Biosciences) or Flow Jo (Tree Star) software.
CD4+ T cell activation assay
Cell populations were flow sorted as described in Ref. 6 to >98% purity. Sorted populations were >95% pure. APCs (2 x 104) were cocultured with 105 CD4+ T cells from the CNS or spleen for 96 h with R10 medium, 5 µg/ml antiCD3, and 200 µM 1-methyl-D-tryptophan (1-MT; Sigma-Aldrich) prepared according to Ref. 12 . Carrier solution alone was added as a control. Cells were assessed for viability by flow cytometry as described above, and cytokines in the supernatants were assessed by cytokine bead array for levels of IL-10, IL-17, and IFN-
according to manufacturers instructions (Upstate Biotechnology).
ELISPOT assays
ELISPOT assays were performed as previously described (13) with 106 cells plus 10 µM PLP139–151.
Immunohistochemistry
Immunohistochemistry was performed on 6-µm-thick frozen cerebellar and lumbar spinal cord sections from PBS-perfused mice as previously described (13). Staining was analyzed using a Leica DM5000B fluorescent microscope and Advanced SPOT software.
Statistical analysis
Differences between groups were determined using an unpaired Students t test and the Mann Whitney U test.
| Results and Discussion |
|---|
|
|
|---|
pDCs are a minor subset of dendritic cells (DCs) in the secondary lymphoid tissues of most mouse strains (14), comprising 23% of DCs and 1.15% of cells in the lymph nodes (LNs) of SJL/J mice (data not shown). Strikingly, CNS infiltrates during EAE contain 37.7% pDCs, 5.4% of the total CNS mononuclear cell population (6). To investigate the role of pDCs during EAE, anti-mPDCA-1 mAb (15) was used to deplete pDCs during EAE onset. One day after pDC depletion, pDCs were depleted from LNs (not shown) (15) and CNS (92.4 ± 0.9% of CNS pDCs) (Fig. 1, A and B). During the relapse phase of EAE, 9 days following pDC depletion the number of CNS pDCs returned to control levels in pDC-depleted animals (Fig. 1A), and, importantly, anti-mPDCA-1 treatment did not affect the numbers of CNS mDCs or macrophages (Fig. 1B). Following pDC depletion, a few mPDCA-1+ cells remained in the meningeal area of the CNS; however, no mPDCA-1+ pDCs were detected in the parenchyma of the spinal cord or cerebellum (Fig. 1C). Inefficient clearing of pDCs from the blood vessel-rich areas of the CNS correlated with low level mPDCA-1 expression on blood CD11c+B220+ pDCs (data not shown).
|
The depletion of pDCs at the onset of R-EAE resulted in a significant exacerbation of peak clinical disease (Fig. 2A). Clinical scores in pDC-depleted mice returned to control levels 2–3 days after the last anti-mPDCA-1 mAb treatment, consistent with a report showing that pDC numbers recover 3–5 days following anti-mPDCA-1 depletion (15). That pDC depletion caused an immediate increase in clinical severity with a rapid return to control levels upon pDC reconstitution suggests that pDCs have a direct, acute regulatory effect on CNS autoimmune disease. pDCs were then depleted during the primary relapse of EAE, leading to enhanced EAE and the abrogation of secondary remission (Fig. 2B).
|
-, and IL-2-producing CD4+ T cells specific for the immunizing peptide in the LNs 1 day following the final mPCDA-1 mAb injection was unchanged compared with controls (Fig. 2C). In fact, PLP139–151-specific Th17 cells were significantly reduced in the spleens of pDC-depleted mice, which may be reflective of reduced EAE severity (3) and not enhanced severity as observed in the clinical experiments. pDCs modulate the activation and frequency of Th1 and Th17 cells in the CNS
Clinical EAE generally correlates with the number and activation status of CNS-infiltrating effector CD4+ T cells and inversely with regulatory T cell (Treg) numbers (17). We found that pDC depletion did not significantly affect the numbers of CNS CD4+ T cells and Foxp3+ CD4+ Tregs (p = 0.2; Fig. 3A). We previously showed that CNS pDCs isolated during EAE poorly activate both naive and activated myelin-specific T cells in comparison to mDCs (6). Because there was little change in the T cell numbers, it is unlikely that the primary function of pDC during EAE is to prime and expand CD4+ T cells in the CNS.
|
in the absence of pDCs. Following pDC depletion, CNS CD4+ T cells were significantly more activated than controls as assessed by down-regulation of CD45RB and up-regulation of CD25 (Fig. 3B). Endogenous production of inflammatory cytokines by CNS CD4+ T cells was determined by incubating CNS isolates, which contain pathogenic T cells and DCs presenting endogenous myelin peptides (6), with GolgiStop for 4 h and then analyzing the accumulated cells expressing IFN-
and IL-17. The frequency of CNS Th17 cells was increased by an average of 1.6 ± 0.38-fold and that of Th1 cells by 1.6 ± 0.27-fold, and more cytokine per cell (enhanced mean fluorescence intensity) were produced in pDC-depleted mice (Fig. 3C). Thus, CNS pDCs promote the accumulation of CD4+ T cells and Tregs in the target organ but strongly modulate the activation status of CD4+ T cells and, importantly, the frequency of CNS Th1 (IFN-
) and Th17 (IL-17) cells.
CNS pDCs actively suppress IL-17, IFN-
, and IL-10 production by CNS CD4+ T cells in an IDO-independent manner
We next sought to determine the mechanism by which pDCs regulate CNS CD4+ T cell activation and cytokine production. pDCs have been implicated in inducing T cell anergy through IFN-
and IL-10 production (18) or TGF-β (19). Using quantitative PCR, we have previously shown that CNS pDCs expressed low levels of TGF-β transcripts (6) and similar levels of IFN-
4 mRNA (not shown) compared with other CNS APCs. In addition, IL-10 levels were lower in CNS pDC-CNS T cell cocultures (Fig. 4A) and CNS pDCs stimulated with CD40L (not shown) compared with CNS mDCs. Based on the low production by CNS pDCs, it is unlikely that TGF-β, IL-10, or IFN-
4 is a dominant pathway for pDC suppression of CD4+ T cells in the CNS.
|
, and IL-10 production by both splenic and CNS-derived T cells (Fig. 4). The IDO inhibitor 1-MT enhanced mDC-induced CD4+ T cell IL-17 and IFN-
secretion and decreased IL-10 production. However, 1-MT had no affect on cytokine production in CD4+ T cells cultured with CNS pDCs. Most profoundly, when CNS pDCs were cocultured with CNS mDC and CNS T cells, production of IL-17, IFN-
,and IL-10 was significantly suppressed (Fig. 4A). These results indicate that CNS pDCs regulate CD4+ T cell cytokines in an active manner that dominates that of mDC-driving Th17 cells in the CNS (6) and that regulation is via an IDO-independent pathway. IFN-β modulates IFN-
and IL-17 production by human PBMCs (21); thus, pDC production of IFN-β (22) may play a primary role in pDC modulation of Th1/Th17 activation during R-EAE concordant with the observation that IFN-β treatment is therapeutic in both EAE and MS (23, 24). We are currently investigating the role of IFN-β production by pDCs during EAE. In summary, we demonstrate an acute, dominant regulatory role for pDCs in CNS autoimmune disease. pDC depletion results in exacerbated EAE but, once pDCs return to normal levels, relapse severity returns to control levels. Normal relapses suggest that the priming of naive T cells in the CNS is unaffected. pDCs suppress mDC-dependent induction/expansion of CNS Th17 and Th1 cells (Fig. 4A). pDC suppression of T cell cytokine production is IDO independent but is not due to the killing of T cells, because in CNS mDC/pDC cocultures CNS CD4+ T cells have enhanced viability (not shown). These data support a dominant regulatory role for pDCs during EAE in that pDCs recruited to the CNS limit pathology by regulating T cell activation and cytokine production. Treatments that support and expand regulatory pDCs may therefore be attractive therapies for T cell-mediated autoimmune diseases.
| Acknowledgments |
|---|
| Disclosures |
|---|
|
|
|---|
| Footnotes |
|---|
1 This work was supported in part by U.S. Public Health Service, National Institutes of Health Research Grant NS-030871, National Multiple Sclerosis Society (NMSS) Research Grant RG 3793-A-7, NMSS Postdoctoral Fellowship Grant FG 1563 A-1 (to S.L.B.), and a grant from the Myelin Repair Foundation. ![]()
2 Address correspondence and reprint requests to Dr. Stephen D. Miller, Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Chicago, IL 60611. E-mail address: s-d-miller{at}northwestern.edu ![]()
3 Abbreviations used in this paper: EAE, experimental autoimmune encephalomyelitis; DC, dendritic cell; LN, lymph node; mDC, myeloid DC; mPDCA, mouse plasmacytoid dendritic cell antigen-1; MS, multiple sclerosis; 1-MT, 1-methyl-D-tryptophan; pDC, plasmacytoid DC; PLP139–151, proteolipid protein peptide 139–151; R-EAE, relapsing EAE; Treg, regulatory T cell. ![]()
Received for publication February 7, 2008. Accepted for publication March 23, 2008.
| References |
|---|
|
|
|---|
in systemic lupus erythematosus. Science 294: 1540-1543.
+B220+ dendritic cells endowed with type 1 interferon production capacity and tolerogenic potential. Blood 100: 383-390.
and IL-17 secretion by activated human PBMC. Cytokine 35: 235-246. [Medline]This article has been cited by other articles:
![]() |
K. L. Graham, B. A. Zabel, S. Loghavi, L. A. Zuniga, P. P. Ho, R. A. Sobel, and E. C. Butcher Chemokine-Like Receptor-1 Expression by Central Nervous System-Infiltrating Leukocytes and Involvement in a Model of Autoimmune Demyelinating Disease J. Immunol., November 15, 2009; 183(10): 6717 - 6723. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. Gao, B. Majchrzak-Kita, E. N. Fish, and J. L. Gommerman Dynamic accumulation of plasmacytoid dendritic cells in lymph nodes is regulated by interferon-{beta} Blood, September 24, 2009; 114(13): 2623 - 2631. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. D. Sharma, D.-Y. Hou, Y. Liu, P. A. Koni, R. Metz, P. Chandler, A. L. Mellor, Y. He, and D. H. Munn Indoleamine 2,3-dioxygenase controls conversion of Foxp3+ Tregs to TH17-like cells in tumor-draining lymph nodes Blood, June 11, 2009; 113(24): 6102 - 6111. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |