A revival of the B cell paradigm for rheumatoid arthritis pathogenesis?

Intravenous Immunoglobulin Controls Th17 Cell-Mediated Osteoclastogenesis

The purpose of this study was to determine the regulatory role of intravenous Ig (IVIg) in Th17 cytokine–induced RANK ligand (RANKL) expression and osteoclast (OC) differentiation from OC precursors (pre-OC). Human CD14⁺ monocytes were isolated and stimulated by Th17 cytokines (IL-17, IL-21, and IL-22) and RANKL expression was investigated using a real-time PCR. CD14⁺ monocytes were incubated with RANKL, Th17 cytokines, and M-CSF, with/without IVIg, and OC differentiation was determined by counting tartrate-resistant acid phosphatase-positive multinucleated cells. OC differentiation was investigated after monocytes were cocultured with Th17 cells in the presence of IVIg. Th17 cell differentiation was determined using enzyme-linked immunosorbent assay and flow cytometry after CD4⁺ T cells were cultured with IVIg under Th17 condition. Th17 cytokines stimulated monocytes to express RANKL and IVIg suppressed the Th17 cytokine-induced RANKL expression. OCs were differentiated when pre-OC were cocultured with RANKL or Th17 cytokines and IVIg reduced the osteoclastogenesis. IVIg also decreased osteoclastogenesis when pre-OC were cocultured with Th17 cells. IVIg decreased both Th17 and Th1 cell differentiation while it did not affect Treg cell differentiation. In summary, IVIg inhibited Th17 cytokine-induced RANKL expression and OC differentiation. IVIg reduced osteoclastogenesis when monocytes were cocultured with Th17 cells. IVIg also reduced Th17 polarization. IVIg could be a new therapeutic option for Th17 cell–mediated osteoclastogenesis.

The human complement receptor type 2 (CR2)/CR1 fusion protein TT32, a novel targeted inhibitor of the classical and alternative pathway C3 convertases, prevents arthritis in active immunization and passive transfer mouse models

Complement activation in human diseases is characterized by the local covalent deposition of the long-lived C3 fragments iC3b/C3dg/C3d. Previously, TT30, a complement alternative pathway (AP)-selective inhibitor, was designed as a fusion protein linking the first four short consensus repeats (SCRs) of human complement receptor type 2 (CR2) with the first five SCRs of human factor H (fH). TT30 acts by utilizing CR2 SCR1-4 to bind the initially formed iC3b/C3dg/C3d fragments and delivering surface-targeted inhibition of AP C3 and C5 convertases through fH SCR 1-5. In order to combine classical (CP) and lectin (LP) pathway inhibitory abilities employing CR2-mediated targeting, TT32 was developed. TT32 is a CR2-CR1 fusion protein using the first ten SCRs of CR1, chosen because they contain both C3 and C5 convertase inhibitory activity through utilization of decay-acceleration and cofactor activity for both AP and CP. In Wieslab assays, TT32 showed potent inhibition of the CP and AP with IC₅₀ of 11 and 46 nM, respectively. The TT32 inhibitory activity is partially blocked with a molar excess of a competing anti-CR2 mAb, thus demonstrating the importance of the CR2 targeting. TT32 was studied in the type II (CII) collagen-induced arthritis (CIA), an active immunization model, and the CII antibody-induced arthritis (CAIA) passive transfer model. In CIA, injection of 2.0 mg TT32 at day 21 and 28 post disease induction, but not untargeted CR1 alone, resulted in a 51.5% decrease in clinical disease activity (CDA). In CAIA, treatment with TT32 resulted in a 47.4% decrease in CDA. Therefore, a complement inhibitor that targets both the AP and CP/LP C3/C5 convertases was shown to limit complement-mediated tissue damage and inflammation in disease models in which all three complement activation pathways are implicated.

Analysis of Characteristics Similar to Autoimmune Disease in Keloid Patients

BACKGROUND

Keloid is a fibrotic skin disease for which immune cell infiltration is a primary pathological hallmark. Meanwhile, in autoimmune diseases, triggering of the inflammation response can lead to tissue injury and subsequent organ fibrosis. When the skin is involved in autoimmune disease, skin fibrosis such as that seen in scleroderma can occur. In this study, we propose that keloid possesses features of autoimmune disease.

METHODS

To verify whether keloid possesses features of autoimmune disease, immune cell infiltration and immune complex deposits were detected with immunohistochemical staining and immunofluorescence, respectively, in keloid and normal skin tissues. A routine antinuclear antibody profile was tested in sera from 28 keloid patients and 28 healthy controls. Lastly, the anti-hnRNPA2B1 autoantibody in sera was evaluated by enzyme-linked immunosorbent assay.

RESULTS

The numbers of CD1α(+) Langerhans cells, CD3(+) T lymphocytes, CD68(+) macrophages, and CD20(+) B lymphocytes increased in keloid tissues compared to normal skin. IgA, IgM, C3, and C1q deposits were found in keloid tissues but not in normal skin, while anti-hnRNPA2B1 levels in sera from keloid patients were elevated.

CONCLUSION

The above findings suggest that keloids have some characteristics that are similar to autoimmune disease and might be mediated by autoimmune responses.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

The role of intravenous immunoglobulins in the treatment of rheumatoid arthritis

Intravenous immunoglobulins (IVIGs) are beneficial and safe for various diseases other than primary immunodeficiencies. Over the years, IVIG has been given for autoimmune diseases as an off-label adjunct therapy. While other biologic agents are indicated for rheumatoid arthritis (RA), IVIG may have a role for specific subgroups of RA patients where anti-cytokine blockers or rituximab may be unwarranted. Such subgroups may include patients with vasculitis, overlap rhupus syndrome, severe infections with active disease, and pregnancy. In addition, IVIG may be considered for juvenile chronic arthritis (JCA) and adult Still's disease. We review the literature for IVIG treatment in RA patients and for these subgroups.

Iguratimod for the treatment of rheumatoid arthritis in Japan

Iguratimod (IGU), a small-molecule compound, was developed as a disease-modifying antirheumatic drug in Japan. The pharmacological studies showed that inhibition of the production of cytokines and immunoglobulins mainly contributes to its improvement effect on animal arthritis models. The first clinical study of IGU in Japanese patients with rheumatoid arthritis was started in 1992 and Phase III studies were started in 1998. From the results of Phase II studies, a dose-escalating regimen was recommended to relieve the side effects. In a double-blind study comparing the efficacy and safety of the drug with those of placebo and salazosulfapyridine, it was confirmed that IGU was superior to placebo and was not inferior to salazosulfapyridine. Furthermore, a double-blind controlled trial of IGU in combination with methotrexate revealed an efficacious and manageable safety profile. IGU would be widely used as a new option for rheumatoid arthritis treatment and combination drug with methotrexate.

The Therapeutic Potential for PI3K Inhibitors in Autoimmune Rheumatic Diseases

The class 1 PI3Ks are lipid kinases with key roles in cell surface receptor-triggered signal transduction pathways. Two isoforms of the catalytic subunits, p110γ and p110δ, are enriched in leucocytes in which they promote activation, cellular growth, proliferation, differentiation and survival through the generation of the second messenger PIP3. Genetic inactivation or pharmaceutical inhibition of these PI3K isoforms in mice result in impaired immune responses and reduced susceptibility to autoimmune and inflammatory conditions. We review the PI3K signal transduction pathways and the effects of inhibition of p110γ and/or p110δ on innate and adaptive immunity. Focusing on rheumatoid arthritis and systemic lupus erythematosus we discuss the preclinical evidence and prospects for small molecule inhibitors of p110γ and/or p110δ in autoimmune disease.

Cytokine-dependent but acquired immunity-independent arthritis caused by DNA escaped from degradation

DNase II digests the chromosomal DNA in macrophages after apoptotic cells and nuclei from erythroid precursors are engulfed. The DNase II-null mice develop a polyarthritis that resembles rheumatoid arthritis. Here, we showed that when bone marrow cells from the DNase II-deficient mice were transferred to the wild-type mice, they developed arthritis. A deficiency of Rag2 or a lack of lymphocytes accelerated arthritis of the DNase II-null mice, suggesting that the DNase II(-/-) macrophages were responsible for triggering arthritis, and their lymphocytes worked protectively. A high level of TNFα, IL-1β, and IL-6 was found in the affected joints of the DNase II-null mice, suggesting an inflammatory-skewed cytokine storm was established in the joints. A lack of TNFα, IL-1β, or IL-6 gene blocked the expression of the other cytokine genes as well and inhibited the development of arthritis. Neutralization of TNFα, IL-1β, or IL-6 had a therapeutic effect on the developed arthritis of the DNase II-null mice, indicating that the cytokine storm was essential for the maintenance of arthritis in the DNase II-deficient mice. Methotrexate, an antimetabolite that is often used to treat patients with rheumatoid arthritis, had a therapeutic effect with the DNase II-null mice. These properties of arthritis in the DNase II-null mice were similar to those found in human systemic-onset juvenile idiopathic arthritis or Still's disease, indicating that the DNase II-null mice are a good animal model of this type of arthritis.

IL-17-producing T cells can augment autoantibody-induced arthritis

Rheumatoid arthritis is a T lymphocyte-mediated disorder, but the precise nature of T cell involvement remains unclear. In the K/BxN mouse model of inflammatory arthritis, T cells initiate disease by providing help to B cells to produce arthritogenic autoantibodies. Here, we have characterized an additional, nonhumoral role for T cells in promoting autoantibody-induced arthritis. Autoreactive KRN T cells introduced either by direct transfer or bone marrow transplantation into B-cell-deficient hosts enhanced K/BxN serum-transferred arthritis, an effect that was dependent on expression of the cognate MHC-molecule/peptide complex. The T cell influence was dependent on interleukin (IL)-17; in contrast, standard serum-transferred arthritis, unenhanced by the addition of T cells, was unaffected by IL-17 neutralization. An IL-17-producing population of transferred KRN T cells was identified and found to be supported by the cotransfer of arthritogenic autoantibodies. IL-17-producing KRN T cells were enriched in inflamed joints of K/BxN mice, suggesting either selective recruitment or preferential differentiation. These results demonstrate the potential for autoreactive T cells to play two roles in the development of arthritis, both driving the production of pathogenic autoantibodies and bolstering the subsequent inflammatory cascade dependent on the innate immune system.

Rituximab therapy in Greek patients with rheumatoid arthritis

OBJECTIVE

An open-label, prospective, uncontrolled study created to investigate clinical response, serological changes and side effects in Greek patients with rheumatoid arthritis (RA), after B-cell depletion with rituximab.

METHODS

Patients with high disease activity (disease activity score [DAS]-28 > 5.1) were selected for treatment with rituximab and received two infusions, 1 gr each, 2 weeks apart. Different disease parameters (visual analog scale, DAS-28, C-reactive protein [CRP], erythrocyte sedimentation rate, health assessment questionnaire, complement (C3), C4, rheumatoid factor [RF], anti-cyclic citrullinated peptide antibody [anti-CCP], swollen joint count, tender joint count, immunoglobulin M [IgM], IgG, IgA) were performed at base line, 2, 4, and 6 months post-treatment. Response was defined according to the American College of Rheumatology (ACR) criteria.

RESULTS

Seventeen patients received therapy. Treatment led to a reduction in various disease parameters. ACR20 was achieved in 41.11% of patients by week 8, 52.94% by week 16, and 82.35% by week 24. ACR50 was achieved in 5.88% by week 8, 41.17% by week 16, and 64.7% by week 24. ACR70 was achieved only by week 24 in 23.52% of patients. Statistical analysis has shown no differences in clinical response, between RF positive/negative patients, and anti-CCP-positive/negative patients, while decline of RF was better correlated with reduction of DAS-28 than with anti-CCP.

CONCLUSIONS

Rituximab is a well tolerated and effective treatment in RA. Response was not correlated to RF or anti-CCP positivity. Decline of RF was associated with clinical response and reduction of DAS-28 and CRP.

The potential of liposomal drug delivery for the treatment of inflammatory arthritis

OBJECTIVE

To review the use of liposomes as a delivery agent in inflammatory arthritis.

METHODS

The literature on liposomes and liposomal drug delivery for the treatment of inflammatory arthritis was reviewed. A PubMed search of articles in the English-language journals from 1965 to 2007 was performed. The index words used were as follows: "rheumatoid arthritis," "liposomes," and "targeted delivery." Papers identified were reviewed, abstracted, and summarized.

RESULTS

Liposomes have the capacity to be used as delivery and targeting agents for the administration of antirheumatic drugs at lower doses with reduced toxicity. In other areas of medicine, the pace of progress has been rapid. In the case of infectious diseases and cancer, liposomal drug delivery has progressed and developed into commercially viable therapeutic options for the treatment of fungal infections (amphotericin B), or metastatic breast cancer and Kaposi sarcoma (doxorubicin, daunorubicin), respectively. In arthritis, the efficacy of prednisolone-loaded long-circulating liposomes is currently being evaluated in a phase II clinical trial. Liposome's application to arthritis is still in its infancy but appears promising as new patents are filed. With improvements in liposomal formulation and targeted synovial delivery, liposomes offer increased therapeutic activity and improvement in the risk-benefit ratio.

CONCLUSION

Recent research into synovial targets and improved liposomal formulations continues to improve our capacity to use liposomes for targeted delivery. With time, this approach has the potential to improve drug delivery and reduce systemic complications.

Fundamental differences in the dynamics of CNS lesion development and composition in MP4- and MOG peptide 35-55-induced experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is characterized by a dynamic inflammatory process in which CNS lesions of distinct cellular composition coexist. In particular the formation of B cell plaques has been ascribed an important role as predictor of disease progression. Here we show that the novel MBP-PLP fusion protein (MP4)-induced experimental autoimmune encephalomyelitis (EAE) of C57BL/6 mice fulfils these criteria inducing differential cellular infiltration of B cells, T cells, macrophages and granulocytes and permitting the quantification and staging of the disease. On the contrary, both key features - dynamic CNS inflammation and B cell infiltration - were absent in the classical MOG:35-55-induced EAE of C57BL/6 mice, which was characterized by a static CD4(+) T cell and macrophage-mediated CNS immunopathology throughout the disease. MP4-induced EAE may thus provide a unique opportunity for studying immune-pathomechanisms of the disease that have been previously neglected due to experimental shortcomings in murine EAE.

Apoptotic cells protect mice from autoimmune inflammation by the induction of regulatory B cells

The maintenance of immune tolerance to apoptotic cells (AC) within an inflammatory milieu is vital to prevent autoimmunity. To investigate this, we administered syngeneic AC i.v. into mice carrying a cohort of ovalbumin (OVA)-specific transgenic T cells (DO11.10) along with OVA peptide and complete Freund's adjuvant, observing a dramatic increase in OVA-specific IL-10 secretion. Activated splenic B cells responded directly to AC, increasing secretion of IL-10, and this programming by AC was key to inducing T cell-derived IL-10. We went on to ask whether AC are able to modulate the course of autoimmune-mediated, chronic inflammation. AC given up to 1 month before the clinical onset of collagen-induced arthritis protected mice from severe joint inflammation and bone destruction. Antigen-specific CD4(+) T cells again secreted significantly more IL-10, associated with a reduced titer of pathogenic anti-collagen II antibodies. Inhibition of IL-10 in vivo reversed the beneficial effects of AC. Passive transfer of B cells from AC-treated mice provided significant protection from arthritis. These data demonstrate that AC exert a profound influence on an adaptive immune response through the generation of CD19(+) regulatory B cells, which in turn are able to influence the cytokine profile of antigen-specific effector T cells.

Clinical characteristics of anti-glucose-6-phosphate isomerase antibody-positive Japanese patients with rheumatoid arthritis

Anti-glucose-6-phosphate isomerase (GPI) antibodies (Abs) are known to be arthritogenic in mice. These Abs are elevated in several forms of arthritic condition in humans, although their prevalence in rheumatoid arthritis (RA) patients is still in debate. Some RA patients have increased levels of anti-GPI Abs, but their clinical manifestation and relevance to other Abs are not clearly elucidated. The aims of this study were to explore the clinical and hematological characteristics of RA with anti-GPI Abs, and to compare their prevalence in RA patients, systemic lupus erythematosus (SLE) patients, and healthy subjects (HS) in a Japanese population. Anti-GPI Abs were positive in 16 patients with RA (12%, n = 137), in 10 patients with SLE (8%, n = 131), and in 6 HS (4%, n = 139). C-reactive protein (CRP), immunoglobulin G, and the antinuclear antibody titer were higher in anti-GPI-positive patients than in those who were negative (P = 0.049, P = 0.0003, and P = 0.002, respectively). Moreover, the positivity of anti-GPI Abs was correlated with CRP more than with rheumatoid factor in RA patients. It is unclear whether anti-GPI Abs can predict the progress of disease, but the prevalence of these Abs was higher in active RA patients with severe arthritis, suggesting that anti-GPI Abs may be related to the pathogenesis of severe forms of arthritis.

In vivo expression pattern of MICA and MICB and its relevance to auto-immunity and cancer

Non-conventional MHC class I MIC molecules interact not with the TCR, but with NKG2D, a C-type lectin activatory receptor present on most NK, gammadelta and CD8(+) alphabeta T cells. While this interaction is critical in triggering/calibrating the cytotoxic activity of these cells, the actual extent of its in vivo involvement, in man, in infection, cancer or autoimmunity, needs further assessment. The latter has gained momentum along with the reported expansion of peripheral CD4(+)CD28(-)NKG2D(+) T cells in rheumatoid arthritis (RA). We first initiated to extend this report to a larger cohort of not only RA patients, but also those affected by systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). In RA and SS, this initial observation was further tested in target tissues: the joint and the salivary glands, respectively. In conclusion and despite occasional and indiscriminate expansion of the previously incriminated T cell subpopulation, no correlation could be observed between the CD4(+)CD28(-)NKG2D(+) and auto-immunity. Moreover, in situ, the presence of NKG2D matched that of CD8(+), but not that of CD4(+) T cells. In parallel, a total body tissue scan of both MICA and MICB transcription clearly shows that despite original presumptions, and with the exception of the central nervous system, both genes are widely transcribed and therefore possibly translated and membrane-bound. Extending this analysis to a number of human tumors did not reveal a coherent pattern of expression vs. normal tissues. Collectively these data question previous assumptions, correlating a tissue-specific expression/induction of MIC in relevance to auto-immune or tumor processes.

PI3K delta and PI3K gamma: partners in crime in inflammation in rheumatoid arthritis and beyond?

Dysregulated signal transduction in innate and adaptive immune cells is known to be associated with the development of various autoimmune and inflammatory diseases. Consequently, targeting intracellular signalling of the pro-inflammatory cytokine network heralds hope for the next generation of anti-inflammatory drugs. Phosphoinositide 3-kinases (PI3Ks) generate lipid-based second messengers that control an array of intracellular signalling pathways that are known to have important roles in leukocytes. In light of the recent progress in the development of selective PI3K inhibitors, and the beneficial effects of these inhibitors in models of acute and chronic inflammatory disorders, we discuss the therapeutic potential of blocking PI3K isoforms for the treatment of rheumatoid arthritis and other immune-mediated diseases.

Auto-antibodies and autoreactive T-cells in rheumatoid arthritis

Rheumatoid arthritis (RA) is not only the most severe of all joint diseases but also the most common systemic autoimmune disease affecting approximately 1% of the world-wide adult population. RA is characterized by the presence of autoantibodies in serum and synovial fluid distinguishing the disease from other arthritides such reactive arthritis or osteoarthritis. Since the historical description of rheumatoid factor (RF), which is an autoantibody directed to immunoglobulin G, numerous additional autoantibodies have been discovered in sera of RA patients. These antibodies may be directed to cartilage components, stress proteins, enzymes, nuclear proteins and, most importantly, citrullinated proteins such as fibrin or vimentin. In contrast to other antibodies including RF, anti-citrullinated protein antibodies are targeted almost exclusively by RA patients thus being the most specific serological markers of RA. Even though most other antibodies are not used for diagnostics, they may contribute to the patholophysiology of RA by forming immune complexes in the joint. Furthermore, autoreactive T-cells in serum and synovial fluid may initiate or enhance the disease process via production of proinflammatory cytokines leading to autoantibody secretion, stimulation of macrophages and activation of bone resorbing osteoclasts. Identification of novel autoantigens, particularly citrullinated proteins, and the characterization of the cellular and molecular processes underlying the autoimmune reactions against them has provided new insights into the complex pathogenesis of RA. This has made possible the development of novel therapeutic concepts that may allow to treat the disease more effectively in its early stages where the chances are highest to interrupt the deleterious processes.

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.

Immunological memory stabilizing autoreactivity

The etiopathologies of autoimmune diseases are complex. A broad variety of cell types and gene products are involved. However, clinical and experimental evidence suggests that the importance of an individual factor changes during the course of the disease. Factors and cell types that induce acute autoreactivity and initiate an autoimmune disease could be distinct from those that drive a chronic course of that disease. Autoreactive immunological memory, in particular B cell and plasma cell memory, contributes to chronicity through several mechanisms. Formation of autoreactive memory B cells leads to an increase in the numbers of autoreactive cells. In comparison to naive B cells, these memory B cells show a decreased threshold for activation. Additionally, a fraction of memory B cells express the chemokine receptor CXCR3, which supports their accumulation within chronically inflamed tissues. This may allow their escape from mechanisms for induction of peripheral tolerance. Within the inflamed tissue, inflammatory cytokines and autoantigens provide activation signals that promote plasma cell differentiation and survival. The autoantibodies produced locally by these plasma cells contribute to the severity of inflammation. Together, an autoreactive loop of autoantibody-induced inflammation is formed. Another integral part of immunological memory are long-lived plasma cells. These cells provide persistent humoral antibody memory. Though not all autoantibodies are produced by long-lived plasma cells, these cells have a special impact on immune pathology. Long-lived plasma cells are relatively resistant to existing therapies of immunosuppression and continuously secrete antibodies, without need for restimulation. Long-lived plasma cells provide titers of autoantibodies even during clinically quiescent phases and after immunosuppression. These persisting autoantibody titers, though often low and not causing acute clinical symptoms, are likely to maintain a low level of chronic inflammation and progressive tissue destruction, which reduces the threshold for another break of immunological tolerance.

B cell depletion therapy in systemic rheumatic diseases: different strokes for different folks?

Autoantibodies have, until recently, been the overriding focus of investigators of autoantibody-associated diseases. Increasing attention is now being paid to B cells, which not only are the producers of autoantibodies but also contribute to autoimmune disease via autoantibody-independent mechanisms. Therapeutic measures that target B cells for depletion are gaining in popularity. In this review, we will focus on two distinct approaches of depleting B cells; one employing a direct-kill approach by engagement of B cell surface CD20 with an anti-CD20 monoclonal antibody (rituximab), and the other employing an indirect starvation approach by neutralization of B lymphocyte stimulator (BLyS), a potent B cell survival factor. Among the systemic immune-based rheumatic disorders, we will focus on rheumatoid arthritis and systemic lupus erythematosus, two disorders for which therapeutic B cell targeting is being intensely investigated.

Immune complex-dependent remodeling of the airway vasculature in response to a chronic bacterial infection

Chronic inflammation in the airways is associated with dramatic architectural changes in the walls of the airways and in the vasculature they contain. In this study, we show that the adaptive immune system is essential for airway remodeling that occurs in mice that are chronically infected with the respiratory pathogen Mycoplasma pulmonis. Angiogenesis, lymphangiogenesis, and epithelial remodeling were greatly reduced in mice that lacked B cells. Substantiating a role for Ab and airway immune complexes, we found that the transfer of immune serum to B cell-deficient mice could reconstitute pathogen-induced angiogenesis. Inflammatory cells recruited to the infected airways were activated by the humoral response, and this activation correlated with the induction of genes for remodeling factors such as vascular endothelial growth factor-D. The results reveal a novel pathway whereby T cell-dependent humoral immunity to a persistent airway infection can induce inflammation-dependent angiogenesis, lymphangiogenesis, and chronic airway pathology.

A crucial role for macrophages in the pathology of K/B x N serum-induced arthritis

Autoantibodies in the form of immune complexes are known to be crucial mediators in initiating inflammation in a variety of autoimmune diseases. This has been well documented in the anti-collagen II antibody-induced arthritis animal model for a long time now. Recently, in the K/B x N mouse model (the F1 of the TCR-transgenic KRN and the diabetic NOD mice), anti-glucose-6-phosphate isomerase (GPI) autoantibodies have been shown to induce arthritis. Experimental work in the K/B x N model demonstrated key roles of autoantigenic immune complexes activating the alternative pathway of complement, the subsequent association with C5aR and Fc gammaRIII-mediated cell activation and production of the inflammatory cytokines IL-1 and TNF-alpha, finally leading to joint destruction. The presence of high amounts of inflammatory cytokines and matrix-degrading proteases at sites of inflammation obviously put the cytokine-producing macrophages as the next target for investigation in this model. Here, we show that mice depleted of macrophages by clodronate liposome treatment are completely resistant to K/B x N serum-induced arthritis. Reconstituting clodronate liposome-treated mice with macrophages from naive animals could reverse this resistance. Also, we found that deficiencies in the Wiskott-Aldrich syndrome protein and CD40, which are both implicated in macrophage activation, chemotaxis and phagocytosis, are not essential in serum-induced arthritis. Mast cell degranulation was seen in arthritogenic serum-treated mice even in the absence of macrophages, possibly suggesting that mast cell degranulation/activation acts hierarchically before macrophages in the inflammatory cascade of anti-GPI antibody-induced arthritis.

Pathogenic autoantibodies: emerging insights into tissue injury

Accumulating evidence is emerging that B lymphocytes and autoantibodies are critical in the development of autoimmune disease. Even in certain disorders initially thought to be T cell-mediated, these immune components are now considered key players in the disease pathogenesis, and new autoantibody specificities have been added to the growing list of targets including cell surface receptors and ion channels that may be involved in a variety of neuropsychiatric and cardiovascular disorders. Studies of autoantibodies penetrating living cells suggest a dosage effect in generating a biological outcome in vivo. Some autoantibodies, such as those directed to double-stranded DNA, can bind to a variety of surrogate antigens located in different cellular compartments, and this may have different biological consequences. This polyreactive behavior could be related to their conformational diversity, or to the fact that the epitope recognized is distributed among other macromolecular antigens. In addition, recent studies revealed unsuspected mechanisms of pathogenesis, wherein autoantibodies have been described that can activate neuronal, endothelial cells or B lymphocytes. Other autoantibodies inactivate the target antigens, or exhibit a catalytic activity, releasing toxic oxygen products that may be linked to arthritic or atherosclerotic injury.

Clinical, laboratory and genetic markers associated with erosions and remission in patients with early inflammatory arthritis: a prospective cohort study

We investigated the relationship between clinical, laboratory and genetic markers and outcome measures in 159 patients with recent onset of inflammatory arthritis (IA). The majority of patients were managed in community-based rheumatology practice. Median duration of arthritis at baseline was 3 months with median follow-up of 4.0 years (range 0-10). Markers of disease activity and 1987 ACR criteria for rheumatoid arthritis (RA) were estimated every 6 months for the first 2 years and annually thereafter. Presence of shared epitopes (SE) was established by PCR-based method. Main outcome variables were attainment of remission and presence of erosions on X-rays of hands and feet at 3 years. Remission was seen in 34.3% of patients and was independently related to age 60 and older (odds ratio (OR) 3.2; 95% confidence interval (CI), 1.2-8.7) and inversely to the presence of rheumatoid factor (RF) (OR 8.3; 95% CI, 3.2-21.3 for persistent arthritis). Patients with two SE were likely to have persistent arthritis (P=0.006), but this was not significant when corrected for RF. Independent predictors for erosions at 3 years were RF (OR 7.5; 95% CI, 1.9-29.5) and area under the curve for number of swollen joints (OR 1.08; 95% CI, 1.02-1.16). SE status was not predictive of erosions at 3 years (OR 1.6; 95% CI, 0.7-3.7). In univariate analysis, patients possessing DERAA motif on DRB1 were less likely to have erosive disease than without this motif at 4 years (OR 0.21; 95% CI, 0.0-0.9, P=0.037) but this finding was partly explained by adjusting for RF (adjusted OR 0.24; 95% CI 0.04-1.37). In this study of recent onset IA, active disease and RF were associated with poor outcome. Whilst SE did not predict erosive disease, patients with DERAA motif may be protected against erosions whilst the presence of two SE alleles suggests persistence of arthritis.

Modulating co-stimulation: a rational strategy in the treatment of rheumatoid arthritis?

Rheumatoid arthritis (RA) is a common destructive inflammatory disease that affects 0.5-1% of the population in many countries. Even though several new treatments have been introduced for patients with RA, a considerable proportion of patients do not benefit from these, and the need for alternative treatment strategies is clear. This review explores the potential for a therapy targeting the adaptive immune system by modulating co-stimulation of T cells with a CTLA4-Ig fusion protein (abatacept).

RANK, RANKL and osteoprotegerin in arthritic bone loss

Rheumatoid arthritis is characterized by the presence of inflammatory synovitis and destruction of joint cartilage and bone. Tissue proteinases released by synovia, chondrocytes and pannus can cause cartilage destruction and cytokine-activated osteoclasts have been implicated in bone erosions. Rheumatoid arthritis synovial tissues produce a variety of cytokines and growth factors that induce monocyte differentiation to osteoclasts and their proliferation, activation and longer survival in tissues. More recently, a major role in bone erosion has been attributed to the receptor activator of nuclear factor kappa B ligand (RANKL) released by activated lymphocytes and osteoblasts. In fact, osteoclasts are markedly activated after RANKL binding to the cognate RANK expressed on the surface of these cells. RANKL expression can be upregulated by bone-resorbing factors such as glucocorticoids, vitamin D3, interleukin 1 (IL-1), IL-6, IL-11, IL-17, tumor necrosis factor-alpha, prostaglandin E2, or parathyroid hormone-related peptide. Supporting this idea, inhibition of RANKL by osteoprotegerin, a natural soluble RANKL receptor, prevents bone loss in experimental models. Tumor growth factor-beta released from bone during active bone resorption has been suggested as one feedback mechanism for upregulating osteoprotegerin and estrogen can increase its production on osteoblasts. Modulation of these systems provides the opportunity to inhibit bone loss and deformity in chronic arthritis.

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.

Apoptotic Effect of Rituximab on Peripheral Blood B Cells in Rheumatoid Arthritis

Rituximab (RTX) has proven efficacious in the treatment of rheumatoid arthritis (RA). Herein, we assessed the apoptosis-inducing capability of RTX in vitro on RA peripheral blood B-cell subsets and also compared the effects of RTX on B cells from rheumatoid factor-positive (RF+) and RF- patients. The likely relevance of B cells in disease was assessed by measuring B-cell-modulating serum cytokines. Peripheral blood B cells were isolated and cultured with the presence or absence of RTX. The levels of apoptosis within the naïve, memory and IgD+CD27+ B-cell subpopulations were determined by cytofluorometric analysis and caspase 3/7 assays. Levels of serum cytokines were measured with a multiplex cytokine array system. RTX induced significant apoptosis in all B-cell subsets in both RA and controls. In naïve and memory B cells from RA patients, RTX induced significantly higher levels of apoptosis than in controls. RTX induced apoptosis of B cells in RF+ and RF- patients. Serum levels of interleukin-1beta (IL-1beta), IL-4, IL-10 and IL-13 were profoundly increased in RF+ patients compared to RF- patients and controls. Although our cohort was small (10 RA patients), the data suggest that RTX induces apoptosis in all investigated subsets of B cells from RA patients. Interestingly, memory B cells from RA patients were more sensitive to RTX than memory cells from normal controls, suggesting that the delay in treatment response to RTX observed in clinical trials may be due in part to memory cell depletion. The apoptotic effects of RTX were similar in RF+ and RF- patients, but serum levels of B-cell-activating cytokine levels were only elevated in RF+ but not RF- patients. These data suggest that RTX is less effective in RF- RA because B cells play a less significant role in RA pathogenesis in RF- patients.

The MHC class I-like Fc receptor promotes humorally mediated autoimmune disease

The MHC class I family-like Fc receptor, FcRn, is normally responsible for extending the life span of serum IgG Ab's, but whether this molecule contributes to autoimmune pathogenesis remains speculative. To determine directly whether this function contributes to humoral autoimmune disease, we examined whether a deficiency in the FcRn heavy chain influences autoimmune arthritis in the K/BxN mouse model. FcRn deficiency conferred either partial or complete protection in the arthritogenic serum transfer and the more aggressive genetically determined K/BxN autoimmune arthritis models. The protective effects of an FcRn deficiency could be overridden with excessive amounts of pathogenic IgG Ab's. The therapeutic saturation of FcRn by high-dose intravenous IgG (IVIg) also ameliorated arthritis, directly implicating FcRn blockade as a significant mechanism of IVIg's anti-inflammatory action. The results suggest that FcRn is a potential therapeutic target that links the initiation and effector phases of humoral autoimmune disease.

RANKL and RANK as novel therapeutic targets for arthritis

The TNF-family molecule receptor activator of nuclear factor kappa B (NFkappaB) ligand (RANKL) (OPGL, TRANCE, ODF) and its receptor activator of NFkappaB (RANK) are key regulators of bone remodeling and regulate T cell/dendritic cell communications, and lymph node formation. Moreover, RANKL and RANK are expressed in mammary gland epithelial cells and control the development of a lactating mammary gland during pregnancy. Genetically, RANKL and RANK are essential for the development and activation of osteoclasts and bone loss in response to virtually all triggers tested. Inhibition of RANKL function via the natural decoy receptor osteoprotegerin (OPG, TNFRSF11B) prevents bone loss in postmenopausal osteoporosis and cancer metastases. Importantly, RANKL appears to be the pathogenetic principle that causes bone and cartilage destruction in arthritis, and OPG treatment prevents bone loss at inflamed joints and has partially beneficial effects on cartilage destruction in all arthritis models studied so far. Modulation of these systems provides a unique opportunity to design novel therapeutics to inhibit bone loss and crippling in arthritis.

Role of RANKL and RANK in bone loss and arthritis

The tumour necrosis factor family molecule RANKL (RANKL, TRANCE, ODF) and its receptor RANK are key regulators of bone remodelling and regulate T cell/dendritic cell communications, and lymph node formation. Moreover, RANKL and RANK are expressed in mammary gland epithelial cells and control the development of a lactating mammary gland during pregnancy and the propagation of mammalian species. Importantly, RANKL and RANK are essential for the development and activation of osteoclasts and bone loss in response to virtually all triggers tested. Therapeutically, inhibition of RANKL function via the decoy receptor osteoprotegerin completely prevents bone loss at inflammed joints and has partially beneficial effects on cartilage destruction in all arthritis models studied. Modulation of these systems provides a unique opportunity to design novel treatments to inhibit bone loss and crippling in arthritis.

Complement deficiency ameliorates collagen-induced arthritis in mice

Collagen-induced arthritis (CIA) is an experimental animal model of human rheumatoid arthritis being characterized by synovitis and progressive destruction of cartilage and bone. CIA is induced by injection of heterologous or homologous collagen type II in a susceptible murine strain. DBA/1J mice deficient of complement factors C3 (C3(-/-)) and factor B (FB(-/-)) were generated to elucidate the role of the complement system in CIA. When immunized with bovine collagen type II emulsified in CFA, control mice developed severe arthritis and high CII-specific IgG Ab titers. In contrast, the C3(-/-) and FB(-/-) were highly resistant to CIA and displayed decreased CII-specific IgG Ab response. A repeated bovine collagen type II exposure 3 wk after the initial immunization led to an increase in the Ab response in all mice and triggered arthritis also in the complement-deficient mice. Although the arthritic score of the C3(-/-) mice was low, the arthritis in FB(-/-) mice ranked intermediate with regard to C3(-/-) and control mice. We conclude that complement activation by both the classical and the alternative pathway plays a deleterious role in CIA.

RANK-L and RANK: T cells, bone loss, and mammalian evolution

TNF and TNFR family proteins play important roles in the control of cell death, proliferation, autoimmunity, the function of immune cells, or the organogenesis of lymphoid organs. Recently, novel members of this large family have been identified that have critical functions in immunity and that couple lymphoid cells with other organ systems such as bone morphogenesis and mammary gland formation in pregnancy. The TNF-family molecule RANK-L (RANK-L, TRANCE, ODF) and its receptor RANK are key regulators of bone remodeling, and they are essential for the development and activation of osteoclasts. Intriguingly, RANK-L/RANK interactions also regulate T cell/dendritic cell communications, dendritic cell survival, and lymph node formation; T cell-derived RANK-L can mediate bone loss in arthritis and periodontal disease. Moreover, RANK-L and RANK are expressed in mammary gland epithelial cells, and they control the development of a lactating mammary gland during pregnancy and the propagation of mammalian species. Modulation of these systems provides us with a unique opportunity to design novel therapeutics to inhibit bone loss in arthritis, periodontal disease, and osteoporosis.

Lessons from animal models of arthritis

There is increasing thought that autoantibodies to systemic self-antigens may provide a principal effector mechanism for the initiation and propagation of joint inflammation. The recent identification of arthritis transfer with antibodies to the self-antigen glucose-6-phosphate isomerase has boosted this interest. Fc receptor involvement in arthritis has been evaluated, identifying pro-inflammatory and inhibitory Fc gamma receptor subtypes, and demonstrating a link between Fc gamma receptor expression, cytokine production, cartilage destruction, and mouse strain susceptibility to immune complex arthritis. Further proof of a key role of interleukin (IL)-1 in arthritis was provided by the occurrence of spontaneous arthritis in IL-1 receptor antagonist knockout mice and elicitation of full-blown arthritis in tumor necrosis factor (TNF)-deficient mice. IL-18 (part of the IL-1 family) is a crucial upstream cytokine that, with IL-12, induces IL-1 and TNF and promotes arthritis and T-cell differentiation. IL-18 neutralization improved arthritis outcome, but its central role in host defense against bacterial infections may complicate therapeutic IL-18 targeting. T helper 1 (Th1) cells may aggravate arthritis and joint destruction through the production of IL-17, which shows joint destructive potential independent of IL-1. Studies have also focused on the control of receptor activator of nuclear factor kappaB ligand, modulation with IL-4, and regulation of downstream mediators in tissue destruction. Gene therapeutic approaches proved efficacious and will provide future ways to control arthritis.