Development of inflammation in proteoglycan-induced arthritis is dependent on Fc gamma R regulation of the cytokine/chemokine environment

FcγRIIB expression increases during primary biliary cholangitis

Primary biliary cholangitis (PBC) is a severe disease with unknown aetiology and poor prognosis owing to ineffective treatment. B-cell antibodies play a regulatory role during immune responses; therefore, their role in PBC should not be overlooked. Fcγ receptors (FcγRs) of IgG and cell surface glycoproteins play an important role in autoimmune and infectious disease prevention. In this study, 60 patients with PBC and 35 healthy controls (HCs) were recruited. The number of B cells and the expression of the FcγRIIB on the peripheral blood mononuclear cells of patients with PBC were evaluated using FACS. The concentrations of soluble FcγRs were determined using ELISA, and intrahepatic FcγRIIB and CD19 expressions in patients with PBC were visualised using IHC. FcγRIIB expression in B cells was significantly higher in patients with PBC than in HCs (P < 0.0001). The soluble FcγRIIB levels in the plasma were higher in patients with PBC than in HCs (P = 0.0009). Notably, these levels were reduced by treatment with ursodeoxycholic acid (P = 0.0236). CD19 and FcγRIIB expression increased in the liver of patients with PBC relative to that in HCs. These findings can provide new insights into PBC pathogenesis and can aid the future development of treatment strategies.

Fc Gamma Receptors as Regulators of Bone Destruction in Inflammatory Arthritis

Bone erosion is one of the primary features of inflammatory arthritis and is caused by excessive differentiation and activation of osteoclasts. Fc gamma receptors (FcγRs) have been implicated in osteoclastogenesis. Our recent studies demonstrate that joint-deposited lupus IgG inhibited RANKL-induced osteoclastogenesis. FcγRI is required for RANKL-induced osteoclastogenesis and lupus IgG-induced signaling transduction. We reviewed the results of studies that analyzed the association between FcγRs and bone erosion in inflammatory arthritis. The analysis revealed the dual roles of FcγRs in bone destruction in inflammatory arthritis. Thus, IgG/FcγR signaling molecules may serve as potential therapeutic targets against bone erosion.

Fc-gamma receptors and S100A8/A9 cause bone erosion during rheumatoid arthritis. Do they act as partners in crime?

Bone erosion is one of the central hallmarks of RA and is caused by excessive differentiation and activation of osteoclasts. Presence of autoantibodies in seropositive arthritis is associated with radiographic disease progression. ICs, formed by autoantibodies and their antigens, activate Fcγ-receptor signalling in immune cells, and as such stimulate inflammation-mediated bone erosion. Interestingly, ICs can also directly activate osteoclasts by binding to FcγRs on their surface. Next to autoantibodies, high levels of alarmins, among which is S100A8/A9, are typical for RA and they can further activate the immune system but also directly promote osteoclast function. Therefore, IC-activated FcγRs and S100A8/A9 might act as partners in crime to stimulate inflammation and osteoclasts differentiation and function, thereby stimulating bone erosion. This review discusses the separate roles of ICs, FcγRs and alarmins in bone erosion and sheds new light on the possible interplay between them, which could fuel bone erosion.

Cytokine-producing B cells: a translational view on their roles in human and mouse autoimmune diseases

B-cell depletion therapy has beneficial effects in autoimmune diseases. This is only partly explained by an elimination of autoantibodies. How does B-cell depletion improve disease? Here, we review preclinical studies showing that B cells can propagate autoimmune disorders through cytokine production. We also highlight clinical observations indicating the relevance of these B-cell functions in human autoimmunity. Abnormalities in B-cell cytokine production have been observed in rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and systemic lupus erythematosus. In the first two diseases, B-cell depletion erases these abnormalities, and improves disease progression, suggesting a causative role for defective B-cell cytokine expression in disease pathogenesis. However, in the last two disorders, the pathogenic role of B cells and the effect of B-cell depletion on cytokine-producing B cells remain to be clarified. A better characterization of cytokine-expressing human B-cell subsets, and their modulation by B cell-targeted therapies might help understanding both the successes and failures of current B cell-targeted approaches. This may even lead to the development of novel strategies to deplete or amplify selectively pathogenic or protective subsets, respectively, which might be more effective than global depletion of the B-cell compartment.

DEC205+ Dendritic Cell-Targeted Tolerogenic Vaccination Promotes Immune Tolerance in Experimental Autoimmune Arthritis

Previous studies in mouse models of autoimmune diabetes and encephalomyelitis have indicated that the selective delivery of self-antigen to the endocytic receptor DEC205 on steady-state dendritic cells (DCs) may represent a suitable approach to induce Ag-specific immune tolerance. In this study, we aimed to examine whether DEC205(+) DC targeting of a single immunodominant peptide derived from human cartilage proteoglycan (PG) can promote immune tolerance in PG-induced arthritis (PGIA). Besides disease induction by immunization with whole PG protein with a high degree of antigenic complexity, PGIA substantially differs from previously studied autoimmune models not only in the target tissue of autoimmune destruction but also in the nature of pathogenic immune effector cells. Our results show that DEC205(+) DC targeting of the PG peptide 70-84 is sufficient to efficiently protect against PGIA development. Complementary mechanistic studies support a model in which DEC205(+) DC targeting leads to insufficient germinal center B cell support by PG-specific follicular helper T cells. Consequently, impaired germinal center formation results in lower Ab titers, severely compromising the development of PGIA. Overall, this study further corroborates the potential of prospective tolerogenic DEC205(+) DC vaccination to interfere with autoimmune diseases, such as rheumatoid arthritis.

Bridging autoantibodies and arthritis: the role of Fc receptors

Autoantibodies represent a hallmark of Rheumatoid arthritis (RA), which is a chronic inflammatory autoimmune disease characterized by inflammation and damage in the joints. Anti-Citrullinated Protein Antibodies (ACPA) are the most prominent autoantibodies present in RA patients. These autoantibodies have been intensively investigated during the last 20 years due to their diagnostic and predictive value. Furthermore, they are believed to be involved in mediating the damage associated with RA. Antibodies of the IgG isotype interact with the immune system via Fcγ receptors expressed on immune cells as well as nonimmune cells. These receptors, therefore, form the bridge between Fcγ receptor-positive cells and antibodies complexed to antigen allowing the modulation and activation of cellular immune responses that are involved in immune defense against invading microorganisms. However, in case triggered by antibodies against self-antigens, they can also play a pivotal role in the induction and perpetuation of autoimmune diseases such as RA. Mouse models have been indispensably important for understanding the role of Fcγ receptors in the development of arthritis. Here we discuss the contribution of autoantibodies to the pathogenesis of arthritis in preclinical animal models, as well as RA, in relation to their interaction with the different (immune inhibitory and activating) Fcγ receptors.

B effector cells in rheumatoid arthritis and experimental arthritis

Rheumatoid arthritis is a chronic autoimmune immune disease affecting approximately 1% of the population. There has been a renewed interest in the role of B cells in rheumatoid arthritis based on the evidence that B cell depletion therapy is effective in the treatment of disease. This review summarizes the current knowledge of the mechanisms by which B cells contribute to autoimmune arthritis including roles as autoantibody producing cells, antigen-presenting cells, cytokine producing cells, and regulatory cells.

Arthritogenic T cells drive the recovery of autoantibody-producing B cell homeostasis and the adoptive transfer of arthritis in SCID mice

T cells orchestrate joint inflammation in rheumatoid arthritis (RA), but B cells/B cell-derived factors are also involved in disease pathogenesis. The goal of this study was to understand the role of antigen-specific T and B cells in the pathological events of arthritis, which is impossible to study in humans due to the small number of antigen-specific cells. To determine the significance of antigen-specific lymphocytes and antibodies in the development of an autoimmune mouse model of RA, we generated TCR transgenic (TCR-Tg) mice specific for the dominant arthritogenic epitope of cartilage proteoglycan (PG) and performed a series of combined transfers of T cells, B cells and autoantibodies into BALB/c.Scid mice. The adoptive transfer of highly purified T cells from naive TCR-Tg, arthritic TCR-Tg or arthritic wild-type mice induced arthritis in SCID recipients, but the onset and severity of the disease were dependent on the sequential events of the T cell-supported reconstitution of PG-specific B cells and autoantibodies. The presence of activated PG-specific T cells was critical for disease induction, establishing a unique milieu for the selective homeostasis of autoantibody-producing B cells. In this permissive environment, anti-PG autoantibodies bound to cartilage and induced activation of the complement cascade, leading to irreversible cartilage destruction in affected joints. These findings may lead to a better understanding of the complex molecular and cellular mechanisms of RA.

Exploiting enzyme specificities in digestions of chondroitin sulfates A and C: production of well-defined hexasaccharides

Interactions between proteins and glycosaminoglycans (GAGs) of the extracellular matrix are important to the regulation of cellular processes including growth, differentiation and migration. Understanding these processes can benefit greatly from the study of protein-GAG interactions using GAG oligosaccharides of well-defined structure. Materials for such studies have, however, been difficult to obtain because of challenges in synthetic approaches and the extreme structural heterogeneity in GAG polymers. Here, it is demonstrated that diversity in structures of oligosaccharides derived by limited enzymatic digestion of materials from natural sources can be greatly curtailed by a proper selection of combinations of source materials and digestive enzymes, a process aided by an improved understanding of the specificities of certain commercial preparations of hydrolases and lyases. Separation of well-defined oligosaccharides can then be accomplished by size-exclusion chromatography followed by strong anion-exchange chromatography. We focus here on two types of chondroitin sulfate (CS) as starting material (CS-A, and CS-C) and the use of three digestive enzymes with varying specificities (testicular hyaluronidase and bacterial chondroitinases ABC and C). Analysis using nuclear magnetic resonance and mass spectrometry focuses on isolated CS disaccharides and hexasaccharides. In all, 15 CS hexasaccharides have been isolated and characterized. These serve as useful contributions to growing libraries of well-defined GAG oligosaccharides that can be used in further biophysical assays.

Characterization of glycosaminoglycans by 15N NMR spectroscopy and in vivo isotopic labeling

Characterization of glycosaminoglycans (GAGs), including chondroitin sulfate (CS), dermatan sulfate (DS), and heparan sulfate (HS), is important in developing an understanding of cellular function and in assuring quality of preparations destined for biomedical applications. While use of (1)H and (13)C NMR spectroscopy has become common in characterization of these materials, spectra are complex and difficult to interpret when a more heterogeneous GAG type or a mixture of several types is present. Herein a method based on (1)H-(15)N two-dimensional NMR experiments is described. The (15)N- and (1)H-chemical shifts of amide signals from (15)N-containing acetylgalactosamines in CSs are shown to be quite sensitive to the sites of sulfation (4-, 6-, or 4,6-) and easily distinguishable from those of DS. The amide signals from residual (15)N-containing acetylglucosamines in HS are shown to be diagnostic of the presence of these GAG components as well. Most data were collected at natural abundance of (15)N despite its low percentage. However enrichment of the (15)N-content in GAGs using metabolic incorporation from (15)N-glutamine added to cell culture media is also demonstrated and used to distinguish metabolic states in different cell types.

Genome-based expression profiling study of Hunner's ulcer type interstitial cystitis: an array of 40-gene model

INTRODUCTION AND HYPOTHESIS

The aim of this study was to explore potential molecular mechanisms contributing to the pathogenesis of Hunner's ulcer type interstitial cystitis (IC).

METHODS

Dataset acquisitions from Gene Expression Omnibus under platform accession no GSE 11783. We compared global gene expression profiles in bladder epithelial cells from IC patients with Hunner's ulcer corresponding to normal controls. We re-sampling and exploit the correlation structure presented in the dataset through the transcriptional response. For each patient, two bladder biopsies were studied, one from an ulcer area and one from a non-ulcer area. RNA was extracted, and all labeled samples were hybridized to Human Genome U133 Plus 2.0 Array (Affymetrix, CA, USA).

RESULTS

The Mahalanobis distance in hierarchical cluster analysis revealed a model of 40 genes expression which is increased in IC and ulcerated IC. Our results can be summarized as follows: First, the expressions of major histocompatibility complex (MHC) class IF and II molecules, leukocyte immunoglobulin-like receptors, hepatitis A virus cellular receptor 2, and interleukin 32 were increased in bladder epithelial from IC and ulcerative IC area. Next, there is an indication of antigen-mediated aggregation of the high-affinity Fc epsilon and gamma RI leading to allergic inflammation through the disease status. Third, the high-affinity Fc gamma RI subunit facilitated T-cell-mediated immune response through the disease status. Such changes, jointly termed "bladder remodeling," can constitute an important long-term consequence of Hunner's ulcer type IC.

CONCLUSIONS

Our results indicate that genome-based expression profiling can be used for the diagnostic tests of Hunner's ulcer type IC in clinical practice.

IFN-gamma regulates the requirement for IL-17 in proteoglycan-induced arthritis

The contribution of the proinflammatory cytokines IFN-gamma and IL-17 to the pathogenesis of experimental arthritis is controversial. In proteoglycan (PG)-induced arthritis (PGIA), severe arthritis is dependent on the production of IFN-gamma, whereas IL-17 is dispensable. In collagen-induced arthritis and Ag-induced arthritis, although high levels of IFN-gamma are secreted, disease is exacerbated in IFN-gamma or IFN-gamma receptor-deficient mice due to the ability of IFN-gamma to suppress IL-17 expression. In the current study, we investigated the effect of IFN-gamma on the IL-17 response and its consequences in PGIA. In PG-immunized IFN-gamma(-/-) mice, despite reduction in arthritis, the PG-specific CD4(+) T cell IL-17 response was significantly increased. Elevated IL-17 contributed to development of arthritis, as disease in IFN-gamma/IL-17(-/-) was significantly reduced in comparison with either IFN-gamma(-/-) or IL-17(-/-) mice. A contribution of IFN-gamma and IL-17 to the development of arthritis was also identified in T-bet(-/-) mice. PG-specific CD4(+) T cells from T-bet(-/-) mice produced reduced IFN-gamma and elevated concentrations of IL-17. Both IFN-gamma and IL-17 contribute to arthritis, as T-bet(-/-) mice lacking IL-17 (T-bet/IL-17(-/-)) were resistant, whereas wild-type, T-bet(-/-), and IL-17(-/-) mice were susceptible to PGIA. T cell proliferation and autoantibody production did not correlate with development of disease; however, expression of cytokines and chemokines in joint tissues demonstrate that IFN-gamma and IL-17 cooperatively contribute to inflammation. These results demonstrate that both IFN-gamma and IL-17 have the potential to induce PGIA, but it is the strength of the IFN-gamma response that regulates the contribution of each of these Th effector cytokines to disease.

Destructive arthritis in the absence of both FcgammaRI and FcgammaRIII

Fc receptors for IgG (FcgammaR) have been implicated in the development of arthritis. However, the precise contribution of the individual FcgammaR to joint pathology is unclear. In this study, the role of the different FcgammaR was assessed both in an active and in a passive mouse model of arthritis by analyzing disease development in double and triple knockout (KO) offspring from crosses of FcgammaRI KO, FcgammaRIII KO, FcgammaRI/III double KO, or FcR gamma-chain KO with the FcgammaRII KO on C57BL6 background, which is susceptible for collagen-induced arthritis (CIA). In the active CIA model, onset was significantly delayed in the absence of FcgammaRIII, whereas incidence and maximum severity were significantly decreased in FcgammaRI/II/III triple KO but not in FcgammaRII/III double KO and FcgammaRI/II double KO mice as compared with FcgammaRII KO animals. Remarkably, fully destructive CIA developed in FcgammaRI/II/III triple KO mice. In contrast, FcR gamma/FcgammaRII double KO mice were resistant to CIA. These findings were confirmed with the passive KRN serum-induced arthritis model. These results indicate that all activating FcgammaR play a role in the development of arthritis, mainly in the downstream effector phase. FcgammaRIII is critically required for early arthritis onset, and FcgammaRI can substantially contribute to arthritis pathology. Importantly, FcgammaRI and FcgammaRIII were together dispensable for the development of destructive arthritis but the FcR gamma-chain was not, suggesting a role for another FcR gamma-chain associated receptor, most likely FcgammaRIV. In addition, FcgammaRII plays a negative regulatory role in both the central and effector phase of arthritis.

Amelioration of collagen-induced arthritis by human recombinant soluble FcgammaRIIb

Immune complex (IC) binding to Fc gamma receptors (FcgammaRs) is central for inflammatory reactions seen in autoimmune diseases. Consequently, a therapeutic agent with a possibility to interfere with binding of pathogenic IC to FcgammaRs would be valuable in autoimmune disorders such as rheumatoid arthritis (RA). Here we have explored the therapeutic effect of a recombinant soluble human FcgammaRIIb (sFcgammaRIIb) protein in collagen-induced arthritis (CIA). In vitro studies of the sFcgammaRIIb demonstrated binding to mouse IgG, suggesting that sFcgammaRIIb can absorb pathogenic IgG anti-collagen type II (CII) IC in vivo. Hence, administration of sFcgammaRIIb significantly reduced CIA severity compared to control treated mice. The sFcgammaRIIb treated mice had significantly less IgG anti-CII antibodies in serum and lower mRNA levels of inflammatory cytokines compared to control mice. In conclusion, sFcgammaRIIb treatment ameliorates CIA by reducing IC-stimulated inflammation and joint swelling. This suggests that recombinant sFcgammaRIIb may be useful as therapeutic agent in RA.

The effect of activating and inhibiting Fc-receptors on murine mercury-induced autoimmunity

Fc-receptors for IgG (FcgammaR) link cellular and humoral immune responses, controlling the balance between activating and inhibitory immune responses, and are involved in autoimmune diseases. Mercury (Hg) induces an autoimmune condition in genetically (H-2(s,q,f)) susceptible mice characterized by lymphoproliferation, hypergammaglobulinemia and IgG antinucleolar antibodies (ANoA). Here we investigate the role of activating (FcgammaRI, FcgammaRIII) and inhibitory (FcgammaRIIb) Fc-receptors on mercury-induced autoimmunity (HgIA) using DBA/1 mice (H-2(q)) with targeted FcgammaR mutations and wild type (wt) mice. Mice deficient for the FcRgamma-chain or FcgammaRIII and treated with 15 mg/L HgCl(2) showed a delayed and attenuated IgG1, IgG2a and IgG2b ANoA response compared to wt mice. Female Hg-treated FcgammaRIIB(-/-) mice showed a significant increased of IgG2b ANoA development compared to wt mice. The total serum IgG1 response due to Hg was attenuated in FcRgamma(-/-) and FcgammaRIII(-/-) mice compared to wt mice. Hg-treated FcgammaRIIB(-/-) mice showed an increase of both serum IgG1 and IgE compared to wt mice. We conclude that FcgammaRIII is of importance for the rapidity and final strength of the ANoA response and the increase in serum IgG1 in HgIA, while lack of FcgammaRIIb increases the IgG2b ANoA response and the serum IgG1 and IgE response.

High synovial expression of the inhibitory FcgammaRIIb in rheumatoid arthritis

Activating Fc gamma receptors (FcγRs) have been identified as having important roles in the inflammatory joint reaction in rheumatoid arthritis (RA) and murine models of arthritis. However, the role of the inhibitory FcγRIIb in the regulation of the synovial inflammation in RA is less known. Here we have investigated synovial tissue from RA patients using a novel monoclonal antibody (GB3) specific for the FcγRIIb isoform. FcγRIIb was abundantly expressed in synovia of RA patients, in sharp contrast to the absence or weak staining of FcγRIIb in synovial biopsies from healthy volunteers. In addition, the expression of FcγRI, FcγRII and FcγRIII was analyzed in synovia obtained from early and late stages of RA. Compared with healthy synovia, which expressed FcγRII, FcγRIII but not FcγRI, all activating FcγRs were expressed and significantly up-regulated in RA, regardless of disease duration. Macrophages were one of the major cell types in the RA synovium expressing FcγRIIb and the activating FcγRs. Anti-inflammatory treatment with glucocorticoids reduced FcγR expression in arthritic joints, particularly that of FcγRI. This study demonstrates for the first time that RA patients do not fail to up-regulate FcγRIIb upon synovial inflammation, but suggests that the balance between expression of the inhibitory FcγRIIb and activating FcγRs may be in favour of the latter throughout the disease course. Anti-inflammatory drugs that target activating FcγRs may represent valuable therapeutics in this disease.

Inhibitory IgG receptor FcgammaRIIB fails to inhibit experimental autoimmune myasthenia gravis pathogenesis

Deficiency of the inhibitory FcgammaRIIB renders mice susceptible to autoimmune disorders characterized with cellular infiltration of target tissue. To analyze the role of FcgammaRIIB in an antibody-mediated autoimmune disease, experimental autoimmune myasthenia gravis (EAMG), FcgammaRIIB knockout (KO) and wild-type mice were immunized with acetylcholine receptor (AChR). In contrast with previous reports, FcgammaRIIB KO mice were mildly resistant to EAMG despite preserved anti-AChR antibody production and neuromuscular junction complement deposition capacity. EAMG resistance was associated with reduced lymph node cell IL-6 and IL-10 production and increased CD4(+)CD25(+) cell ratios in lymph nodes. Our data suggest that FcgammaRIIB promotes antibody-mediated autoimmunity.

B cell depletion delays collagen-induced arthritis in mice: arthritis induction requires synergy between humoral and cell-mediated immunity

Rheumatoid arthritis is a systemic autoimmune disease. B cells are likely to play a critical role in arthritis pathogenesis, although it is unclear whether they are necessary for disease induction, autoantibody production, or disease progression. To assess the role of B cells in inflammatory arthritis, B cells were depleted using mouse anti-mouse CD20 mAbs in a mouse model of collagen-induced arthritis. CD20 mAbs effectively depleted mature B cells from adult DBA-1 mice. When B cells were depleted using CD20 mAbs before collagen immunization, there was a delay in disease onset and autoantibody production, with significantly diminished severity of arthritis both clinically and histologically. B cell depletion further delayed disease onset if initiated before, as well as after, collagen immunization. However, in both cases, the eventual reappearance of peripheral B cells triggered autoantibody production and the subsequent development of arthritis in collagen-sensitized mice. By contrast, B cell depletion after collagen immunizations did not have a significant effect on arthritis progression or severity. Thus, disease symptoms were only induced when peripheral B cells and their autoantibody products were present in collagen-immunized mice, documenting a critical role for B cells during the elicitation phase of collagen-induced arthritis. These studies suggest that B cell depletion strategies will be most effective when initiated early in the development of inflammatory arthritis, with sustained B cell depletion required to inhibit the production of isotype-switched pathogenic Abs and the evolution of joint inflammation and destruction.

FcR-bearing myeloid cells are responsible for triggering murine lupus nephritis

Lupus glomerulonephritis is initiated by deposition of IgG-containing immune complexes in renal glomeruli. FcR engagement by immune complexes (IC) is crucial to disease development as uncoupling this pathway in FcRgamma(-/-) abrogates inflammatory responses in (NZB x NZW)F1 mice. To define the roles of FcR-bearing hemopoietic cells and of kidney resident mesangial cells in pathogenesis, (NZB x NZW)F1 bone marrow chimeras were generated. Nephritis developed in (NZB x NZW)F1 mice expressing activating FcRs in hemopoietic cells. Conversely, recipients of FcRgamma(-/-) bone marrow were protected from disease development despite persistent expression of FcRgamma in mesangial cell populations. Thus, activating FcRs on circulating hemopoietic cells, rather than on mesangial cells, are required for IC-mediated pathogenesis in (NZB x NZW)F1. Transgenic FcRgamma(-/-) mice expressing FcRgamma limited to the CD11b+ monocyte/macrophage compartment developed glomerulonephritis in the anti-glomerular basement disease model, whereas nontransgenic FcRgamma(-/-) mice were completely protected. Thus, direct activation of circulating FcR-bearing myeloid cells, including monocytes/macrophages, by glomerular IC deposits is sufficient to initiate inflammatory responses.

The role of fibroblasts and fibroblast-derived factors in periprosthetic osteolysis

OBJECTIVE

This study was undertaken to investigate how fibroblasts respond to stimulation with particulate wear debris and/or conditioned media obtained from pathologic tissue, and whether these activated fibroblasts express compounds that are involved in bone resorption.

METHODS

Conditioned media from explant cultures of synovial tissue, periprosthetic soft tissue (interface membranes), titanium particles, and proinflammatory cytokines were used to stimulate fibroblasts. RNase protection assay was used to measure altered gene expression, and enzyme-linked immunosorbent assay, Western blot hybridization, and flow cytometry were used to determine fibroblast protein expression. Tartrate-resistant acid phosphatase staining was used to identify multinucleated osteoclast-like cells.

RESULTS

The most dominant compounds measured in the conditioned media from interface membranes were tumor necrosis factor alpha (TNFalpha), monocyte chemoattractant protein 1 (MCP-1), interleukin-1beta (IL-1beta), IL-6, IL-8, and vascular endothelial growth factor. Fibroblasts phagocytosed particulate wear debris and responded to cytokine/chemokine stimulation. The most prominent up-regulated genes and proteins secreted by fibroblasts in response to stimulation were matrix metalloproteinase 1, MCP-1, IL-1beta, IL-6, IL-8, cyclooxygenase 1 (COX-1), COX-2, leukemia inhibitory factor 1, transforming growth factor beta1 (TGFbeta1), and TGFbeta receptor type I. In addition, interface membrane fibroblasts expressed RANKL and osteoprotegerin in response to stimulation with conditioned media, TNFalpha, or IL-1beta. Stimulated fibroblasts cocultured with bone marrow cells in the presence of macrophage colony-stimulating factor induced osteoclastogenesis.

CONCLUSION

Interface membrane fibroblasts respond directly to particulate wear debris, possibly via phagocytosis, expressing proinflammatory cytokines and RANKL. Thus, these cells may be actively involved in osteoclastogenesis and pathologic (periprosthetic) bone resorption.

The complex role of Fcγ receptors in the pathology of arthritis

Autoantibodies of the IgG class and the immune complexes they form are central players in the pathology of rheumatoid arthritis (RA). Receptors for the Fc part of IgG, FcgammaR constitute one of the main effector mechanisms through which IgG immune complexes exert their action. The different members of the FcgammaR family exhibit extensive structural homology leading to redundancy in ligand specificity and signal transduction. Moreover, the initiation of effector mechanisms by IgG immune complexes can also be mediated by the complement system. This strong redundancy and high degree of complexity hampers a direct in vivo analysis of antibody effector pathways. Over the last decade, mice deficient for different combinations of FcgammaR have been generated by gene targeting. These knockout mice provide excellent tools to define the specific contribution of the different FcgammaR to IgG effector pathways in well-established in vivo mouse models for arthritis. This review will discuss the results of the studies that analyze the role of the different members of the FcgammaR family in murine arthritis models and their implications for our understanding of the human disease.

Genetic evidence for the involvement of Fcγ receptor III in experimental autoimmune myasthenia gravis pathogenesis

Immune complexes and classical complement pathway play vital roles in experimental autoimmune myasthenia gravis (EAMG). To analyze the role of immune complex receptors in EAMG, FcgammaRIII knockout (KO) mice were immunized with AChR and were found out to be resistant to EAMG induction. This was associated with reduced neuromuscular junction deposits, lymph node cell (LNC) IL-6 production and serum complement levels. EAMG resistance of anti-C1q Ab-administered mice was also associated with reduced LNC IL-6 production and neuromuscular junction deposits, indicating C1q involvement in EAMG resistance. The data provide the first direct genetic evidence for Fcgamma receptor involvement in EAMG pathogenesis.

Increased arthritis susceptibility in cartilage proteoglycan–specific T cell receptor–transgenic mice

OBJECTIVE

To better understand the role of antigen (arthritogenic epitope)-specific T cells in the development of autoimmune arthritis.

METHODS

A transgenic (Tg) mouse expressing the T cell receptor (TCR) Valpha1.1 and V(beta)4 chains specific for a dominant arthritogenic epitope (designated 5/4E8) of human cartilage proteoglycan (HuPG) aggrecan was generated. This TCR-Tg mouse strain was backcrossed into the PG-induced arthritis (PGIA)-susceptible BALB/c strain and tested for arthritis incidence and severity.

RESULTS

CD4+ TCR-Tg T cells carried functionally active TCR specific for a dominant arthritogenic epitope of HuPG (5/4E8). T cells of naive TCR-Tg mice were in an activated stage, since the in vitro response to HuPG or to peptide stimulation induced interferon-gamma and interleukin-4 production. TCR-Tg mice uniformly, without exception, developed severe and progressive polyarthritis, even without adjuvant. Inflamed joints showed extensive cartilage degradation and bone erosions, similar to that seen in the arthritic joints of wild-type BALB/c mice with PGIA. Spleen cells from both naive and HuPG-immunized arthritic TCR-Tg mice could adoptively transfer arthritis when injected into syngeneic BALB/c.SCID recipient mice.

CONCLUSION

TCR-Tg BALB/c mice display increased arthritis susceptibility and develop aggravated disease upon in vivo antigen stimulation. This model using TCR-Tg mice is a novel and valuable research tool for studying mechanisms of antigen (arthritogenic epitope)-driven regulation of arthritis and understanding how T cells recognize autoantigen in the joints. This type of mouse could also be used to develop new immunomodulatory strategies in T cell-mediated autoimmune diseases.

Molecular manipulation with the arthritogenic epitopes of the G1 domain of human cartilage proteoglycan aggrecan

Systemic immunization of BALB/c mice with human cartilage proteoglycan (PG) aggrecan induces progressive polyarthritis. The G1 domain of the PG aggrecan molecule contains most of the T cell epitopes, including three immunodominant ('arthritogenic') and at least six subdominant T cell epitopes. The three dominant T cell epitopes (P49, P70 and P155) were deleted individually or in combination by site directed mutagenesis, and the recombinant human G1 (rhG1) domain (wild type and mutated) proteins were used for immunization. Close to 100% of BALB/c mice immunized with the wild-type (nonmutated) rhG1 domain developed severe arthritis, which was 75% in the absence of P70 (5/4E8) epitope, and very low (< 10% incidence) when all three dominant T cell epitopes were deleted. The onset was delayed and the severity of arthritis reduced in animals when dominant T cell epitopes were missing from the immunizing rhG1 domain. The lack of T cell response to the deleted epitope(s) was specific, but the overall immune response against the wild-type rhG1 domain of human PG was not significantly affected. This study helped us to understand the dynamics and immune-regulatory mechanisms of arthritis, and supported the hypothesis that the development of autoimmune arthritis requires a concerted T cell response to multiple epitopes, rather than the immune response to a single arthritogenic structure.

IgG Fc receptor polymorphisms and association with autoimmune disease

The aim of this study was to investigate whether a genetic polymorphism of Fc gammaRIII exists in mice, which could explain the different susceptibility to pathogenic IgG anti-collagen type II (CII) antibodies in mice carrying the collagen-induced arthritis (CIA)-susceptible H-2q haplotype. The gene for Fc gammaRIII was sequenced in 11 common mouse strains, and the results revealed three different haplotypes of mouse Fc gammaRIII: Fc gammaRIII:V, Fc gammaRIII:H and Fc gammaRIII:T. To study the consequences of this polymorphism, we generated mice carrying the Fc gammaRIII:H haplotype from the CIA-susceptible, H-2q-positive DBA/1 mouse or the Fc gammaRIII:V haplotype from the CIA-resistant, H-2q-positive SWR mouse. After CII immunization or transfer of IgG anti-CII antibodies, Fc gammaRIII:H-expressing mice, but not Fc gammaRIII:V-expressing mice, developed progressively severe arthritis. We also investigated if C5, in addition to Fc gammaRIII polymorphism, could affect the susceptibility to the pathogenic IgG anti-CII antibodies in H-2q-positive mice. Here we show that SWR mice, naturally deficient in C5, can develop CIA when supplemented with C5 and that anti-C5 antibody treatment of Fc gammaRIII:H-expressing mice inhibits arthritis development. These data demonstrate for the first time a genetic polymorphism of Fc gammaRIII in mice that may, together with C5, regulate induction of autoimmune disease.

Tendon xanthomas in familial hypercholesterolemia are associated with a differential inflammatory response of macrophages to oxidized LDL

Tendon xanthomas (TX) are pathognomonic lipid deposits commonly found in familial hypercholesterolemia (FH) patients. The aim of this study was to determine whether macrophages from FH patients with TX (TX+) have higher predisposition to foam cells formation after oxidized LDL (oxLDL) overload than those from FH patients without TX (TX-), and if their differential gene expression profile could explain these different phenotypes. Total RNA pools from macrophages from FH patients TX+ and TX- were analyzed using Affymetrix oligonucleotide arrays to evaluate the gene expression profile in presence and absence of oxLDL. Also, the intracellular lipid content was measured by fluorescence flow cytometry. Results of these studies suggest that macrophages from FH subjects TX+ compared to those TX- have a differential response to oxLDL, since they show higher intracellular cholesterol ester accumulation and a differential gene expression profile. The gene array data were validated by relative quantitative real-time RT-PCR and quantitative ELISA in culture media and plasma samples. FH subjects TX+ showed increased plasma tryptase, TNF-alpha, IL-8 and IL-6 concentrations. We propose that TX formation are associated with higher intracellular lipid content, and higher inflammatory response of macrophages in response to oxLDL.

Development of proteoglycan-induced arthritis is critically dependent on Fcγ receptor type III expression

OBJECTIVE

To study the necessity for activating Fcgamma receptor types I and III (FcgammaRI and FcgammaRIII) in proteoglycan-induced arthritis (PGIA), a murine model of rheumatoid arthritis, and to determine whether usage of FcgammaRI or FcgammaRIII correlates with the Th1 phenotype or the autoantibody isotype in PGIA.

METHODS

PGIA was induced by immunizing FcgammaRI(-/-), FcgammaRIII(-/-), and wild-type (WT) littermate mice with human PG. The development and severity of arthritis were monitored over time. PG-specific T cell interleukin-2 (IL-2) production and B cell antibody responses were assessed. FcgammaRIII blocking antibodies were used to inhibit arthritis in an adoptive transfer system. Inflammation in the hind paws was evaluated by assessing cytokine and chemokine messenger RNA (mRNA) transcripts by real-time polymerase chain reaction.

RESULTS

FcgammaRI(-/-) mice developed arthritis with similar kinetics and severity as WT littermate controls, whereas FcgammaRIII(-/-) mice failed to develop the disease. Both FcgammaRI(-/-) and FcgammaRIII(-/-) mice produced similar amounts of PG-specific antibody and IL-2 as littermate controls. Transfer of arthritis was successfully blocked in mice treated with a blocking antibody against FcgammaRIII. FcgammaRIII(-/-) mice displayed a significant decrease in cytokine and chemokine mRNA transcripts obtained from the hind paws of immunized mice, whereas FcgammaRI(-/-) mice demonstrated a similar increase in cytokine and chemokine transcripts as controls.

CONCLUSION

These results demonstrate that FcgammaRIII expression is critical to the development of PGIA, and usage of FcgammaRIII correlates with the IgG1 isotype of the PG-specific antibody response. FcgammaRIII expression appears to be important in the effector phase of arthritis, possibly by activating cytokine- and chemokine-secreting cells in the joint.

Antigen-specific B cells are required as APCs and autoantibody-producing cells for induction of severe autoimmune arthritis

B cells play an important role in rheumatoid arthritis, but whether they are required as autoantibody-producing cells as well as APCs has not been determined. We assessed B cell autoantibody and APC functions in a murine model of autoimmune arthritis, proteoglycan (PG)-induced arthritis, using both B cell-deficient mice and Ig-deficient mice (mIgM) mice that express an H chain transgene encoding for membrane-bound, but not secreted, IgM. The IgH transgene, when paired with endogenous lambda L chain, recognizes the hapten 4-hydroxy-3-nitro-phenyl acetyl and is expressed on 1-4% of B cells. B cell-deficient and mIgM mice do not develop arthritis after immunization with PG. In adoptive transfer of PG-induced arthritis into SCID mice, T cells from mIgM mice immunized with PG were unable to transfer disease even when B cells from PG-immunized wild-type mice were provided, suggesting that the T cells were not adequately primed and that Ag-specific B cells may be required. In fact, when PG was directly targeted to the B cell Ig receptor through a conjugate of 4-hydroxy-3-nitrophenyl acetyl-PG, T cells in mIgM mice were activated and competent to transfer arthritis. Such T cells caused mild arthritis in the absence of autoantibody, demonstrating a direct pathogenic role for T cells activated by Ag-specific B cells. Transfer of arthritic serum alone induced only mild and transient arthritis. However, both autoreactive T cells and autoantibody are required to cause severe arthritis, indicating that both B cell-mediated effector pathways contribute synergistically to autoimmune disease.

Immune complexes as therapy for autoimmunity

For several decades, intravenous Ig has been used as treatment for a variety of immune-related diseases, including immune thrombocytopenic purpura (ITP), autoimmune neuropathies, systemic lupus erythematosus, myasthenia gravis, Guillain-Barré syndrome, skin blistering syndromes, and Kawasaki disease. Despite years of use, its mechanism of immunomodulation is still unclear. Recent studies using mouse models of ITP and arthritis, including one reported in this issue of the JCI, now provide some insights into this mechanism and the rationale for the development of Fcgamma receptor-targeted therapeutics.

The Inhibitory Co-Receptor, PECAM-1 Provides a Protective Effect in Suppression of Collagen-Induced Arthritis

Studies of PECAM-1(-/-) mice have identified that PECAM-1 functions as an inhibitory co-receptor to modulate immunological responsiveness. In this study, we describe the in vivo consequences of PECAM-1 deficiency in mouse models of collagen-induced arthritis (CIA) and K/BxN passive transfer model that resembles many of the features of human rheumatoid arthritis. Immunization of PECAM-1(-/-) C57BL/6 (H-2b) mice with chicken collagen type II induced CIA with an incidence of 82% by day 49, while 33%; of wild-type and 100% of DBA/1 mice developed arthritis in a similar time frame. The mean onset of disease for PECAM-1(-/-) C57BL/6 mice was day 32 compared to day 51 for wild-type C57BL/6 mice and day 18 for DBA/1 mice (H-2q susceptible). In terms of disease severity, the mean maximal arthritic index for PECAM-1(-/-) C57BL/6 mice was comparable to DBA/1 mice (8.91 +/- 0.91 vs 11.67 +/- 0.82). This mean maximal index in PECAM-1(-/-) C57BL/6 mice was significantly higher than wild-type C57BL/6 mice (5.00 +/- 0.73). IgG1 and IgG2b antibody responses against CII were elevated in arthritic PECAM-1(-/-) C57BL/6 mice compared to wild-type C57BL/6 mice. Histological examination of arthritic paws of PECAM-1(-/-) C57BL/6 mice revealed inflammatory infiltrates of lymphocytic/monocytic cells and cartilage/bone destruction similar to CIA-induced DBA/1 arthritic paws. In the K/BxN model, the arthritis was not augmented in PECAM-1(-/-) mice compared to wild-type mice. In contrast, in active CIA, PECAM-1(-/-) mice developed severe disease comparable to susceptible DBA/1 mice and profoundly more severe than C57BL/6 mice, where only one third developed a mild/moderate disease. Together these observations suggest that PECAM-1 plays a crucial role in the suppression of development of autoimmune arthritis.

Fcgamma receptors in the initiation and progression of systemic lupus erythematosus

Systemic lupus erythematosus, a systemic autoimmune disorder, is characterized by the production of autoantibodies to nuclear constituents and inflammatory lesions in multiple organ systems. Although the pathogenesis of the disease is largely unknown, recent studies have suggested that disturbances in apoptosis and/or clearance of apoptotic cells may play an important role in the induction and perpetuation of autoantibody production. When autoantibodies subsequently complex to autoantigens present on apoptotic cells, ligation of Fcgamma receptor will result in inflammation and disease development. Indeed, mice deficient in activating Fcgamma receptors were protected against inflammation in models of immune complex-mediated autoimmune disease, whereas deletion of the inhibitory Fcgamma receptors increased autoantibody production and susceptibility to immune complex-induced inflammation. Additionally, functional polymorphisms in Fcgamma receptors were shown to be associated with development of human systemic lupus erythematosus. This review focuses on the role of Fcgamma receptors in the initiation of autoantibody production, inflammatory handling of immune complexes, and disease development in systemic lupus erythematosus.

Inhibition of interleukin 10 signaling after Fc receptor ligation and during rheumatoid arthritis

Interleukin-10 (IL-10) is a potent deactivator of myeloid cells that limits the intensity and duration of immune and inflammatory responses. The activity of IL-10 can be suppressed during inflammation, infection, or after allogeneic tissue transplantation. We investigated whether inflammatory factors suppress IL-10 activity at the level of signal transduction. Out of many factors tested, only ligation of Fc receptors by immune complexes inhibited IL-10 activation of the Jak-Stat signaling pathway. IL-10 signaling was suppressed in rheumatoid arthritis joint macrophages that are exposed to immune complexes in vivo. Activation of macrophages with interferon-gamma was required for Fc receptor-mediated suppression of IL-10 signaling, which resulted in diminished activation of IL-10-inducible genes and reversal of IL-10-dependent suppression of cytokine production. The mechanism of inhibition involved decreased cell surface IL-10 receptor expression and Jak1 activation and was dependent on protein kinase C delta. These results establish that IL-10 signaling is regulated during inflammation and identify Fc receptors and interferon-gamma as important regulators of IL-10 activity. Generation of macrophages refractory to IL-10 can contribute to pathogenesis of inflammatory and infectious diseases characterized by production of interferon-gamma and immune complexes.