Cytokine production in synovial tissue of mice with collagen-induced arthritis (CIA)

The kinetics of cytokine production in arthritic limbs of mice with CIA was determined by using modified immunohistochemical techniques. Tissue cryostat sections of undecalcified whole paws were analysed for the presence of tumour necrosis factor-alpha (TNF-α), IL-6, IL-2, IL-4, IL-5 interferon-gamma (IFN-γ), transforming growth factor-beta 2 (TGF-β2) and TGF-β3. Locally produced TNF-α, IL-6 and TGF-β2 were observed within the lining layer, sublining and pannus at all stages of disease. The staining of TNF-α was particularly intense at the cartilage–pannus junction. In contrast to the monokines, IFN-γ and TGF-β3 were only expressed in scattered cells within the deeper layers of the synovia. Interestingly, IFN-γ was not present in the late phase of CIA, despite the continued presence of TNF-α and IL-6 in the pannus. Production of IL-2, IL-4 or IL-5 was not detected in any joint. The observed pattern of a relative paucity of T cell-derived cytokines and an abundance of monokines during the late phase of T cell-dependent CIA indicates that the synovial cytokine pattern previously described in rheumatoid arthritis (RA) is fully compatible with a pathogenic role of T cells. The temporal as well as spatial dissociation between expression of T cell-derived cytokines and monokines indicates that T cell-independent mechanisms may also be of importance in the triggering of monokine production during arthritis.     

Myeloid-Derived Suppressor Cells Protect Mouse Models from Autoimmune Arthritis via Controlling Inflammatory Response

Myeloid-derived suppressor cells (MDSCs) have been reported to participate in immune suppression and autoimmune disorders. However, its role in autoimmune arthritis remains to be determined. We explored whether adoptive transfer of MDSCs in vivo would block joint inflammation and histological damage using collagen-induced arthritis (CIA) and antigen-induced arthritis (AIA) models. CD11b⁺ Gr-1⁺ MDSCs were isolated from the single cells from the spleens of CIA mice on day 41 or AIA mice on day 35. MDSCs (2?×?10⁶) were then transferred to AIA and CIA mice via tail vein before arthritis establishment at indicated time points. Phosphate buffered saline (PBS) was injected as control. Arthritis was evaluated by severity score and histology. The levels of TNF-α, IL-6, IL-17 and IL-10 in the serum and joints were detected by enzyme-linked immunosorbent assay (ELISA). The number of Th17 cells and macrophages in draining lymph nodes and joint tissues was assessed by flow cytometric analysis. Adoptive transfer of MDSCs significantly reduced the clinical score of arthritis, alleviated joint inflammation and histological damage both in AIA and CIA models compared with PBS-treated control groups. The levels of TNF-α, IL-6, IL-17, and IL-10 in the serum and joints were down-regulated by transfer of MDSCs. In addition, adoptive transfer of MDSCs significantly reduced the number of Th17 cells and macrophages in draining lymph nodes and joint tissues. Altogether, we demonstrate that adoptive transfer of MDSCs prevented autoimmune arthritis in mouse models of RA through inhibiting Th17 cells and macrophages. These new findings provide insights into the inhibitory functions of MDSCs and MDSCs may be used as a cell-based biotherapy in RA.     

Lymphocyte-activation gene 3+ (LAG3+) forkhead box protein 3− (FOXP3−) regulatory T cells induced by B cells alleviates joint inflammation in collagen-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune disease in which dysregulated immune cells primarily target synovial joints. Despite recent advances in the treatment of RA, including the introduction of biologic therapies and employment of combination disease-modifying antirheumatic drug strategies, remission rates remain suboptimal. Previous studies have demonstrated that the adoptive transfer of induced regulatory T cells (iTregs) was effective in treating a murine model of collagen-induced arthritis (CIA). The objective of this study was to develop optimal potential iTreg-based therapy for CIA by adoptively transferring LAG3⁺ Treg-of-B cells. B-cell-induced Treg-of-B cells expressed LAG3 but not Foxp3 (designated LAG3⁺ Treg-of-B), and secreted IL-4, IL-10, and TGF-β. Furthermore, LAG3⁺ Treg-of-B cells suppressed the proliferation of CD4⁺CD25⁻ responder T cells through both LAG3 and IL-10 production. In the murine CIA model, adoptive transfer of LAG3⁺ Treg-of-B cells alleviated the joint severity as well as local and systemic inflammation. Treatment with LAG3⁺ Treg-of-B cells also promoted IL-10 production in lymphocytes isolated from the spleen and draining lymph nodes. Moreover, mice receiving LAG3⁺ Treg-of-B cell treatment showed significantly less pronounced osteolysis in the hind footpads, which correlated with the downregulation of tartrate-resistant acid phosphatase expression. In conclusion, we identified a novel subset of Tregs for CIA treatment. This insight may facilitate exploring novel regulatory T-cell-based therapies for human autoimmune diseases.     

Toll-like receptor 2 ligand mediates the upregulation of angiogenic factor, vascular endothelial growth factor and interleukin-8/CXCL8 in human rheumatoid synovial fibroblasts

Rheumatoid arthritis (RA) is characterized by infiltrations of inflammatory cells accompanied by neovascularization in the joint. We hypothesized that cell activation via the toll-like receptor (TLR) may be involved in the induction of angiogenic molecules, which are relevant to the pathogenesis of RA. RA fibroblast like synoviocytes (FLS) were stimulated with TLR-2 ligand bacterial peptidoglycan (PGN), TLR-4 ligand lipopolysaccharide (LPS) and various cytokines. Vascular endothelial growth factor (VEGF) and IL-8 were measured by ELISA in culture supernatants; mRNA levels were assessed by RT-PCR and real time PCR. The levels of TLR-2, VEGF and IL-8 were analyzed by dual immunohistochemistry in RA synovium and compared with osteoarthritis (OA). Regulation of MyD88, IRAK4, IRAK1, IRAK-M and TRAF-6 mRNA expression levels by PGN were analyzed by RT-PCR. Phosphorylation of I kappa B alpha was evaluated by western blotting. Levels of VEGF and IL-8 were upregulated in culture supernatants of RA FLS stimulated with PGN, similar to the levels of IL-1beta and IL-17 stimulation. Neutralization of TLR-2 with a blocking monoclonal antibody significantly reduced both VEGF and IL-8 levels (P<0.05), which reflected the functional relevance of TLR-2 activation to the induction of VEGF and IL-8 production. Downstream intracellular signaling following TLR-2 stimulation involved MyD88-IRAK-4-TRAF-6 pathways, resulting in NF-kappaB activation. Thus, TLR-2 activation in RA FLS by microbial constituents could be involved in the induction of VEGF and IL-8 and thereby promote inflammation either directly or via angiogenesis. This possibly contributes to the perpetuation of synovitis in patients with RA.     

Enhanced and persistent levels of interleukin (IL)‐17+CD4+ T cells and serum IL‐17 in patients with early inflammatory arthritis

Prognosis of patients with early inflammatory arthritis (EIA) is highly variable. The aim of this study was to compare, longitudinally and cross-sectionally, the levels of cytokine-expressing cells in peripheral blood (PB) from patients with EIA to those in established rheumatoid arthritis (RA) and healthy controls (HC). PB mononuclear cells from HC (n = 30), patients with EIA (n = 20) or RA (n = 38) were stimulated with phorbol myristate acetate (PMA)/ionomycin for 3 h, and stained for cell markers and cytokines. Serum cytokines and chemokines were measured by Luminex. Patients with EIA were reassessed at 6 and 12 months. The percentage of interleukin (IL)-17⁺interferon (IFN)-γ⁻CD4⁺ T cells [T helper type 17 (Th17)] was increased in RA and EIA versus HC. Serum IL-1β, IL-2, IL-4 IL-17 and macrophage inflammatory protein (MIP)-1α were increased in RA and EIA versus HC. IL-1Ra, IL-15 and IFN-α were increased in EIA versus HC. IL-6 and tumour necrosis factor (TNF)-α was increased in RA but not EIA versus HC. Disease activity scores in EIA patients improved over 12 months'' treatment. Th17 percentage at baseline was correlated with both rheumatoid factor (RF) titre and functional deficit at 12 months. Baseline levels of serum granulocyte–macrophage colony-stimulating factor (GM-CSF), IL-6 and IL-8 were correlated with Larsen score at 12 months. There were no significant changes in cytokine-expressing CD4⁺T cells over time, although the percentage of IL-6⁺ monocytes increased. IL-17⁺CD4⁺ T cells and serum IL-17 levels are increased in EIA. IL-6-expressing monocytes increase during the first year of disease, irrespective of disease-modifying anti-rheumatic drug (DMARD) therapy. We observed incomplete clinical responses, suggesting EIA patients need more intensive early therapy.     

Depletion of γδ+ T cells increases CD4+ FoxP3 (T regulatory) cell response in coxsackievirus B3-induced myocarditis

Coxsackievirus B3 (CVB3) causes severe myocarditis in BALB/c mice which depends upon CD4⁺ T helper type 1 [Th1; i.e. interferon-γ⁺ (IFN-γ⁺)] and γδ⁺ cells. Depleting γδ⁺ cells using anti-γδ antibody suppresses myocarditis and CD4⁺ IFN-γ⁺ cell numbers in the spleen and heart of infected mice while increasing CD4⁺ FoxP3⁺ cells. Mice deficient in γδ⁺ cells have increased numbers of naïve (CD44^lo CD62L^hi) and fewer effector (CD44^hi CD62^lo) memory CD4⁺ cells than infected γδ⁺-cell-sufficient mice. Virus neutralizing antibody titres are not significantly different between γδ⁺ T-cell-sufficient and -deficient animals. To confirm that the memory cell response differs in acutely infected mice lacking γδ⁺ cells, CD4⁺ cells were purified and adoptively transferred into naïve recipients, which were rested for 4 weeks then infected with CVB3. Recipients given either 0·5 × 10⁶ or 1·0 × 10⁶ CD4⁺ from infected donors developed over twice the severity myocarditis and 10-fold less cardiac virus titre compared with recipients given equivalent numbers of CD4⁺ cells from infected and γδ⁺-cell-depleted donor animals. Additionally, to show that more functionally active T regulatory cells are present in γδ⁺ T-cell-depleted mice, CD4⁺ CD25⁺ and CD4⁺ CD25⁻ cells were isolated and adoptively transferred into infected recipients. Mice receiving CD4⁺ CD25⁺ cells from γδ⁺ T-cell-depleted donors developed significantly less myocarditis and CD4⁺ Th1 cell responses compared with mice receiving equal numbers of CD4⁺ CD25⁺ cells from infected γδ⁺ T-cell-sufficient animals. This study shows that γδ⁺ cells promote CD4⁺ IFN-γ⁺ acute and memory responses by limiting FoxP3⁺ T regulatory cell activation.     

Abundance of intraepithelial γδ T cells in hypertrophic obstructive but not in chronically infected adenoids

Using quantitative morphometric analysis of immunohistochemically stained tissue sections we compared hypertrophic obstructive adenoids (HOA, n = 10) from children without middle ear disease with chronically infected adenoids (CIA, n = 10) from children with middle ear disease. γδ T cell receptor (TCR)⁺ cells constituted the dominating T cell population in the surface epithelium of HOA, while αβ TCR⁺ cells were the dominating intraepithelial T cell population in CIA. Intraepithelially CD8⁺ cells dominated over CD4⁺ cells in both diseases. Intraepithelially B cells were not detected. The cellular composition of follicles, with B cells dominating followed by activated CD4⁺αβ TCR⁺ cells, was the same in both groups. However, the number of follicles in CIA was twice as many as in HOA. In the deeper interfollicular areas granulocytes were more abundant in CIA than in HOA. The latter two findings suggest a more pronounced inflammatory response in the adenoids of patients with middle ear disease. There was no significant difference with regard to pathogenic bacterial strains colonizing the adenoid surface when comparing the two patient groups. These results suggest that in patients with HOA γδ TCR⁺ T cells help to maintain the integrity of the surface epithelium, thereby preserving its protective function. On the basis of our results we speculate that CIA have a malfunctioning defence, thereby facilitating long-standing infections deep in the adenoid. This may be the main reason for development of middle ear disease and an indication for adenoidectomy in patients with CIA.     

Rheumatoid arthritis fibroblast‐like synoviocytes co‐cultured with PBMC increased peripheral CD4+CXCR5+ICOS+ T cell numbers

‘Circulating’ T follicular helper cells (Tfh), characterized by their surface phenotypes CD4⁺chemokine receptor 5 (CXCR5)⁺ inducible co‐stimulatory molecule (ICOS)⁺, have been identified as the CD4⁺ T cell subset specialized in supporting the activation, expansion and differentiation of B cells. Fibroblast‐like synoviocytes (FLS) are critical in promoting inflammation and cartilage destruction in rheumatoid arthritis (RA), and the interaction between FLS and T cells is considered to facilitate FLS activation and T cell recruitment. However, it remains unknown whether RA‐FLS co‐cultured with activated peripheral blood mononuclear cells (PBMC) has immunoregulatory effects on peripheral Tfh. In the present study, we co‐cultured RA‐FLS with or without anti‐CD3/CD28‐stimulated PBMC. The results showed that RA‐FLS co‐cultured with stimulated PBMC could increase the numbers of CD4⁺CXCR5⁺ICOS⁺ T cells of RA PBMC possibly via the production of interleukin (IL)‐6, a critical cytokine involved in the differentiation of Tfh cells. We also observed increased reactive oxygen species (ROS) levels in the co‐culture system of RA‐FLS and PBMC. The percentage of CD4⁺CXCR5⁺ICOS⁺ T cells was decreased when ROS production was inhibited by N‐acetyl‐L‐cysteine (NAC), a specific inhibitor which can decrease ROS production. In addition, we showed that the higher levels of tumour necrosis factor (TNF)‐α and IL‐1β in the co‐culture system and the blocking of TNF receptor 2 (TNF‐R2) and IL‐1β receptor (IL‐1βR) both decreased the numbers of CD4⁺CXCR5⁺ICOS⁺ T cells. Our study reveals a novel mechanistic insight into how the interaction of RA‐FLS and PBMC participates in the RA pathogenesis, and also provides support for the biologicals application for RA.     

Spatiotemporal expression of endogenous TLR4 ligands leads to inflammation and bone erosion in mouse collagen‐induced arthritis

Increased expression of endogenous Toll‐like receptor 4 (TLR4) ligands (e.g., Tenascin‐C, S100A8/A9, citrullinated fibrinogen (cFb) immune complexes) has been observed in patients with rheumatoid arthritis (RA). However, their roles in RA pathogenesis are not well understood. Here, we investigated the expression kinetics and role of endogenous TLR4 ligands in the murine model of collagen‐induced arthritis (CIA). Tenascin‐C was upregulated in blood early in CIA, and correlated positively with the clinical score at day 56. Levels of S100A8/A9 increased starting from day 28, peaking at day 42, and correlated positively with joint inflammation. Levels of anti‐cFb antibodies increased during the late phase of CIA and correlated positively with both joint inflammation and cartilage damage. Blockade of TLR4 activation at the time of the first TLR4 ligand upregulation prevented clinical and histological signs of arthritis. A TLR4‐dependent role was also observed for Tenascin‐C and cFb immune complexes in osteoclast differentiation in vitro. Taken together, our data suggests that the pathogenic contribution of TLR4 in promoting joint inflammation and bone erosion during CIA occurs via various TLR4 ligands arising at different stages of disease. The data also suggests that Blockade of TLR4 with monoclonal antibodies is a promising strategy in RA treatment.     

HMGB1 Promotes the Differentiation of Th17 via Up‐Regulating TLR2 and IL‐23 of CD14+ Monocytes from Patients with Rheumatoid Arthritis

High‐mobility group box 1 (HMGB1) is a non‐histone nuclear protein that is released extracellulary and has been implicated in autoimmune disease. Toll‐like receptor 2 (TLR2) signalling is thought to be essential for the inflammatory response and for immune disorders. In recent studies, enhanced HMGB1 and TLR2 expressions have been found in rheumatoid arthritis (RA), respectively. The aim of this study is to explore whether HMGB1 stimulation can up‐regulate the expression of TLR2 on CD14⁺ monocytes from patients with RA and to clarify the subsequent events involving Th17 cells and Th17 cell‐associated cytokine changes. Our results showed that the frequency of CD14⁺ cells in peripheral blood mononuclear cell (PBMC) was obviously increased, and enhanced expression of TLR2 on CD14⁺ monocytes was also found in patients with RA, compared with healthy controls with statistical significance (P < 0.001). In addition, the levels of IL‐17, IL‐23 and IL‐6 in supernatants from cultured monocytes from patients and in patient’s plasma were increased, and NF‐κB, the downstream target of TLR2, also showed a marked elevation after monocytes were stimulated by HMGB1. This implies that the enhanced TLR2 pathway and Th17 cell polarization may be due to HMGB1 stimulation in rheumatoid arthritis.     

Treatment of collagen‐induced arthritis by Natura‐α via regulation of Th‐1/Th‐17 responses

Cytokines and CD4⁺ Th cells play a crucial role in the pathogenesis of rheumatoid arthritis. Among the Th populations, Th‐1 and Th‐17 have been described as pathogenic in collagen‐induced arthritis (CIA) whereas Th‐2 and Treg were found to have protective effects. The objective of this study was to examine the affect of Natura‐α, a newly developed cytokine regulator, on CIA and on Th cell development. Natura‐α treatment was administered before or during arthritis induction. Anti‐type II collagen antibodies and cytokine expression were evaluated by ELISA. Emergence of CD4⁺CD25⁺Foxp3⁺ T cells was assessed by flow cytometry. Th‐17 differentiation of naive CD4 T cells was assessed in cultures with anti‐CD3 and anti‐CD28. We showed that Natura‐α both prevented and treated CIA. We further demonstrated that in vivo treatment with Natura‐α inhibited IL‐17 production and anti‐type II collagen IgG development. We showed in vitro, using an APC‐free system, that Natura‐α acted directly on differentiating T cells and inhibiting the formation of Th‐1 and Th‐17 cells but did not affect Th‐2 cells. Since Natura‐α inhibits a large spectrum of important pathogenic factors in CIA, it may provide a new and powerful approach to the treatment of rheumatoid arthritis and other inflammatory diseases.     

Increased expression of beta-arrestin 1 and 2 in murine models of rheumatoid arthritis: isoform specific regulation of inflammation

Pro-inflammatory cytokines and chemokines play critical roles in autoimmune diseases including rheumatoid arthritis (RA). Recently, it has been reported that β-arrestin 1 and 2 are involved in the regulation of inflammation. We hypothesized that β-arrestin 1 and 2 play critical roles in murine models of RA. Using a collagen-induced arthritis (CIA) and a human TNFα transgenic (TNFtg) mouse model, we demonstrated that β-arrestin 1 and 2 expression are significantly increased in joint tissue of CIA mice and TNFtg mice. In fibroblast-like synoviocytes (FLS) isolated from hind knee joint of CIA mice, we observed an increase of β-arrestin 1 and 2 protein and mRNA levels in the early stage of arthritis. In FLS, low molecular weight hyaluronan (HA)-induced TNFα and IL-6 production was increased by overexpression of β-arrestin 1 but decreased by overexpression of β-arrestin 2 demonstrating isoform specific regulation. TNFα and HA induced an increase of β-arrestin 1 and 2 expression in FLS, while high mobility group box (HMGB)-1 only stimulated β-arrestin 1 expression. TNFα- or HA-induced β-arrestin 2 expression was blocked by a p38 inhibitor. To examine the in vivo role of β-arrestin 2 in the pathogenesis of arthritis, WT and β-arrestin 2 KO mice were subjected to collagen antibody-induced arthritis (CAIA). β-Arrestin 2 KO mice exhibited more severe arthritis in CAIA. Thus β-arrestin 2 is anti-inflammatory in CAIA. These composite observations suggest that β-arrestin 1 and 2 differentially regulate FLS inflammation and increased β-arrestin 2 may reduce experimental arthritis severity.     

Increased numbers of CD5+ B cells and T cell receptor (TCR) γδ+ T cells are associated with younger age of onset in rheumatoid arthritis (RA)

Patients presenting with RA before the age of 45 years (younger onset) are known to have more aggressive disease compared with patients presenting after the age of 65 years (older onset). Coordinated expansion of circulating CD5⁺ B cell and TCR γδ⁺ T cell levels has been reported in patients with RA. This study assesses the peripheral blood levels of these two cell types in RA patients with younger and older onset of disease. CD5⁺ B cell levels were significantly elevated in the younger onset RA group (26·6 ± 4·5%) compared with the older onset RA group (14·2 ± 1·2%; P <0·01). TCR γδ⁺ T cell levels were also significantly raised in the young patients (4·0 ± 0·9%) compared with elderly patients (1·6 ± 0·2%; P <0·01). T cell levels (CD3⁺) were similar in both groups (young 66·4 ± 3·3%; old 74·3 ± 3·4% (mean ± s.e.m.); NS). Total B cell levels (CD19⁺) were also similar in these groups (7·7 ± 0·7% versus 8·9 ± 1·8%; NS). A significant positive correlation was observed between the CD5⁻ B and TCR γδ⁺ T cell types in the patients (r = 0·72, P <0.05). Compared with age-matched normal controls, the younger onset patients had similar CD5⁺ B cell and TCR γδ⁺ T cell levels to the elderly controls (CD5⁺ B cells 30·2 ± 3·0%; TCR γδ⁺ T cells 3·0 ± 0·8%). Conversely, older onset RA patients had CD5⁺ B cell levels similar to the young controls (12·3 ± 1·9%). Spontaneous in vitro synthesis of immunoglobulins (IgM, IgA and IgG) and rheumatoid factors (IgM and IgA isotypes) were not significantly different in both patient groups. The coordinate expansion of circulating CD5⁺ B cells and γδ⁺ T cells seen in patients with RA presenting before 45 years of age and not after 65 years of age may suggest a potential role for these cells in more aggressive disease states.     

SUMO-Conjugating Enzyme UBC9 Promotes Proliferation and Migration of Fibroblast-like Synoviocytes in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease with high morbidity and mortality. Fibroblast-like synoviocytes (FLS) in the synovial tissues play critical roles in joint destruction. Recent studies implicate the sumoylation in the regulation of the inflammation and arthritis. Thus, we explored whether SUMO-conjugating enzyme UBC9 is involved in the progression of RA using a mouse collagen-induced arthritis (CIA) model. The effects of UBC9 siRNA on cell invasion and migration in human RA-FLS were also assessed in vitro. Treatment with siRNA against UBC9 for 3 weeks reduced the arthritis score and joint destruction. The expression of SUMO-1 and UBC9 protein in CIA joints was inhibited by UBC9 knockdown. Serum levels of anti-collagen (CII) antibodies, vascular endothelial growth factor A (VEGF-A), matrix metalloproteinases (MMP)-3, and MMP-9 were also decreased in CIA mice. In vitro, UBC9 silencing inhibited the secretion of VEGF-A, MMP-3, and MMP-9 from TNF-α-stimulated human RA-FLS. TNF-α-induced RA-FLS proliferation and migration were significantly attenuated by UBC9 knockdown. These findings indicate that SUMO-conjugating enzyme UBC9 promotes proliferation and migration of fibroblast-like synoviocytes in rheumatoid arthritis. Inhibition of UBC9 activity may be a viable therapeutic target in amelioration of disease progression in RA by attenuating FLS proliferation, migration, and invasion.     

Functional characterization of myeloid‐derived suppressor cell subpopulations during the development of experimental arthritis

Recent evidence indicates the existence of subpopulations of myeloid‐derived suppressor cells (MDSCs) with distinct phenotypes and functions. Here, we characterized the role of MDSC subpopulations in the pathogenesis of autoimmune arthritis in a collagen‐induced arthritis (CIA) mouse model. The splenic CD11b⁺Gr‐1⁺ MDSC population expanded in CIA mice, and these cells could be subdivided into polymorphonuclear (PMN) and mononuclear (MO) MDSC subpopulations based on Ly6C and Ly6G expression. During CIA, the proportion of splenic MO‐MDSCs was increased in association with the severity of joint inflammation, while PMN‐MDSCs were decreased. MO‐MDSCs expressed higher levels of surface CD40 and CD86 protein, but lower levels of Il10, Tgfb1, Ccr5, and Cxcr2 mRNA. PMN‐MDSCs exhibited a more potent capacity to suppress polyclonal T‐cell proliferation in vitro, compared with MO‐MDSCs. Moreover, the adoptive transfer of PMN‐MDSCs, but not MO‐MDSCs, decreased joint inflammation, accompanied by reduced levels of serum cytokine secretion and the frequencies of Th1 and Th17 cells in draining lymph nodes. These results suggest that there could be a shift from potently suppressive PMN‐MDSCs to poorly suppressive MO‐MDSCs during the development of experimental arthritis, which might reflect the failure of expanded MDSCs to suppress autoimmune arthritis.     

Deacetylase inhibition increases regulatory T cell function and decreases incidence and severity of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an established mouse model of disease with hallmarks of clinical rheumatoid arthritis. Histone/protein deacetylase inhibitors (HDACi) are known to inhibit the pathogenesis of CIA and other models of autoimmune disease, although the mechanisms responsible are unclear. Regulatory T cell (Treg) function is defective in rheumatoid arthritis. FOXP3 proteins in Tregs are present in a dynamic protein complex containing histone acetyltransferase and HDAC enzymes, and FOXP3 itself is acetylated on lysine residues. We therefore investigated the effects of HDACi therapy on regulatory T cell function in the CIA model. Administration of an HDACi, valproic acid (VPA), significantly decreased disease incidence (p < 0.005) and severity (p < 0.03) in CIA. In addition, VPA treatment increased both the suppressive function of CD4⁺CD25⁺ Tregs (p < 0.04) and the numbers of CD25⁺FOXP3⁺ Tregs in vivo. Hence, clinically approved HDACi such as VPA may limit autoimmune disease in vivo through effects on the production and function of FOXP3⁺ Treg cells.     

CD8α⁺ dendritic cells improve collagen-induced arthritis in CC chemokine receptor (CCR)-2 deficient mice

Objective

Dendritic cells (DCs) have long been recognized as potential therapeutic targets of rheumatoid arthritis (RA). Increasing evidence has showed that DCs are capable of suppressing autoimmunity by expanding FoxP3⁺ regulatory T cells (T_reg), which in turn exert immunosuppression by increasing TGFβ-1. In the SKG mice, activated DC prime autoreactive T cells causing autoantibody production and an inflammatory arthritic response. Recently, we reported that CC-chemokine receptor-2 deficient (Ccr2^−/−) mice had impaired DCs migration and reduced CD8α⁺ DCs in the C57Bl/6J mice strain and that these mice were more susceptible to collagen antibody-induced arthritis (CAIA), compared to wild type mice. To examine the mechanism by which DCs contribute to the increased susceptibility of arthritis in Ccr2^−/− mice, we tested the hypothesis that CD8α⁺ DCs are protective (tolerogenic) against autoimmune arthritis by examining the role of CD8α⁺ DCs in Ccr2^−/− and SKG mice.

Methods

To examine the mechanism by which DCs defects lead to the development of arthritis, we used two murine models of experimental arthritis: collagen-induced arthritis (CIA) in DBA1/J mice and zymosan-induced arthritis in SKG mice. DBA1/J mice received recombinant fms-like tyrosine kinase 3 ligand (Flt3L) injections to expand endogenous DCs populations or adoptive transfers of CD8α⁺ DCs.

Results

Flt3L-mediated expansion of endogenous CD8α⁺ DCs resulted in heightened susceptibility of CIA. In contrast, supplementation with exogenous CD8α⁺ DCs ameliorated arthritis in Ccr2^−/− mice and enhanced TGFβ1 production by T cells. Furthermore, SKG mice with genetic inactivation of CCR2 did not affect the numbers of DCs nor improve the arthritis phenotype.

Conclusion

CD8α⁺ DCs were tolerogenic to the development of arthritis. CD8α⁺ DCs deficiency heightened the sensitivity to arthritis in Ccr2^−/− mice. Ccr2 deficiency did not alter the arthritic phenotype in SKG mice suggesting the arthritis in Ccr2^−/− mice was T cell-independent.