Ras guanine nucleotide-releasing protein-4 (RasGRP4) involvement in experimental arthritis and colitis

RasGRP4 (Ras guanine nucleotide-releasing protein-4) is an intracellular, calcium-regulated guanine nucleotide exchange factor and diacylglycerol/phorbol ester receptor expressed in mast cells (MCs) and their progenitors. To study the function of this signaling protein in inflammatory disorders, a homologous recombination approach was used to create a RasGRP4-null C57BL/6 mouse line. The resulting transgenic animals had normal numbers of MCs in their tissues that histochemically and morphologically resembled those in WT C57BL/6 mice. MCs could also be generated from RasGRP4-null mice by culturing their bone marrow cells in IL-3-enriched conditioned medium. Despite these data, the levels of the transcripts that encode the proinflammatory cytokines IL-1β and TNF-α were reduced in phorbol 12-myristate 13-acetate-treated MCs developed from RasGRP4-null mice. Although inflammation was not diminished in a Dermatophagoides farinae-dependent model of allergic airway disease, dextran sodium sulfate-induced colitis was significantly reduced in RasGRP4-null mice relative to similarly treated WT mice. Furthermore, experimental arthritis could not be induced in RasGRP4-null mice that had received K/BxN mouse serum. The latter findings raise the possibility that the pharmacologic inactivation of this intracellular signaling protein might be an effective treatment for arthritis or inflammatory bowel disease.

Hypogalactosylation of serum N-glycans fails to predict clinical response to methotrexate and TNF inhibition in rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is associated with hypogalactosylation of immunoglobulin G (IgG). We examined whether a proxy measure for galactosylation of IgG N-glycans could predict response to therapy or was differentially affected by methotrexate (MTX) or TNF blockade.

Methods

Using a previously defined normal phase high-performance liquid chromatography approach, we ascertained the galactosylation status of whole serum N-glycans in two well-defined RA clinical cohorts: the Autoimmune Biomarkers Collaborative Network (n = 98) and Nested I (n = 64). The ratio of agalactosylated to monogalactosylated N-glycans in serum (sG0/G1) was determined before and during therapy with MTX or TNF inhibition and correlated with anticitrullinated peptide antibody (ACPA) status and clinical response as assessed by 28-joint Disease Activity Score utilizing C-reactive peptide and European League Against Rheumatism response criteria.

Results

RA patients from both cohorts exhibited elevation of sG0/G1 at baseline. Improvement in clinical scores correlated with a reduction in sG0/G1 (Spearman's ρ = 0.31 to 0.37; P < 0.05 for each cohort). However, pretreatment sG0/G1 was not predictive of clinical response. Changes in sG0/G1 were similar in the MTX and TNF inhibitor groups. Corrected for disease activity, ACPA positivity correlated with higher sG0/G1.

Conclusions

Baseline serum N-glycan hypogalactosylation, an index previously correlated with hypogalactosylation of IgG N-glycans, did not distinguish patients with rheumatoid arthritis who were likely to experience a favorable clinical response to MTX or TNF blockade. Clinical improvement was associated with partial glycan normalization. ACPA-positive patients demonstrated enhanced N-glycan aberrancy compared with ACPA-negative patients.

Clinical comparison of early-onset psoriatic and non-psoriatic oligoarticular juvenile idiopathic arthritis

OBJECTIVES

Among the seven subtypes of juvenile idiopathic arthritis (JIA), oligoarticular JIA (oJIA) and psoriatic JIA (psJIA) display a predilection for onset in early childhood. We examined whether meaningful differences in clinical phenotype justify the distinction between these conditions.

METHODS

We performed a chart review to identify children with psoriatic and non-psoriatic oligoarticular-onset JIA. Clinical and demographic features of the two groups of children were compared.

RESULTS

Of the 390 children included in the study, 303 met the criteria for oJIA and 87 met the criteria for oligoarticular-onset psJIA. Both groups had a peak age of onset at 2-3 years, though psJIA had appreciable incidence into adolescence. Onset before 5 years of age was observed in 215 (71%) and 38 (44%) children respectively (p<0.001). Within this age category, children with psJIA demonstrated similar gender ratio and anti-nuclear antibody status to those with oJIA but exhibited a distinctive clinical pattern, with a tendency to involve the wrists and small joints of the hands and feet. Conversely, among all children presenting with oligoarthritis in early childhood, those with wrist or small joint involvement were more likely to have nail pits, psoriasis, or a family history of psoriasis than those without (p<0.05), supporting the association of this joint pattern with the psoriatic diathesis.

CONCLUSIONS

Even taking into account age of onset and number of joints, oJIA and psJIA remain clinically distinct, though important demographic overlap remains. These findings support separate diagnostic categories but justify further investigation into the similarities as well as differences among these children.

Anakinra as first-line disease-modifying therapy in systemic juvenile idiopathic arthritis: report of forty-six patients from an international multicenter series

OBJECTIVE

To examine the safety and efficacy of the interleukin-1 (IL-1) receptor antagonist anakinra as first-line therapy for systemic juvenile idiopathic arthritis (JIA).

METHODS

Patients with systemic JIA receiving anakinra as part of initial disease-modifying antirheumatic drug (DMARD) therapy were identified from 11 centers in 4 countries. Medical records were abstracted using a standardized instrument, and resulting data were analyzed to characterize concomitant therapies, clinical course, adverse events, and predictors of outcome.

RESULTS

Among 46 patients meeting inclusion criteria, anakinra monotherapy was used in 10 patients (22%), while 67% received corticosteroids and 33% received additional DMARDs. Outcomes were evaluated at a median followup interval of 14.5 months. Fever and rash resolved within 1 month in >95% of patients, while C-reactive protein and ferritin normalized within this interval in >80% of patients. Active arthritis persisted at 1 month in 39% of patients, at 3 months in 27%, and at >6 months of followup in 11%. Approximately 60% of patients, including 8 of 10 receiving anakinra monotherapy, attained a complete response without escalation of therapy. Disease characteristics and treatment were similar in partial and complete responders, except that partial responders were markedly younger at onset (median age 5.2 years versus 10.2 years; P = 0.004). Associated adverse events included documented bacterial infection in 2 patients and hepatitis in 1 patient. Tachyphylaxis was not observed.

CONCLUSION

Anakinra as first-line therapy for systemic JIA was associated with rapid resolution of systemic symptoms and prevention of refractory arthritis in almost 90% of patients during the interval examined. These results justify further study of IL-1 inhibition as first-line, rather than rescue, therapy in systemic JIA.

C5a receptor enables participation of mast cells in immune complex arthritis independently of Fcγ receptor modulation

OBJECTIVE

Mast cells are tissue-resident immune sentinels that are implicated in the pathogenesis of inflammatory joint disease. The aim of this study was to test our hypothesis that complement fragments could be key activators of synovial mast cells in autoimmune arthritis.

METHODS

In vivo studies used the murine K/BxN arthritis model, a distal symmetric polyarthritis mediated by IgG immune complexes. Expression of C5aR on synovial mast cells was determined by immunohistochemical and functional studies. C5aR(-/-) and control mast cells were engrafted into mast cell-deficient WBB6 F1-Kit(w) /Kit(W-v) (W/Wv) mice to examine the requirement for this receptor in arthritis. C5aR-dependent activation of mast cells was investigated in C5aR(-/-) animals and in murine and human mast cell cultures.

RESULTS

Murine synovial mast cells express functional C5aR. Unlike their wild-type counterparts, C5aR(-/-) mast cells adoptively transferred into W/Wv mice were not competent to restore arthritis, despite equivalent synovial engraftment. Activation of C5aR(-/-) mast cells by K/BxN serum in vivo remained intact, indicating that C5aR is dispensable for normal IgG-mediated triggering. Consistent with this result, cultured mast cells treated with C5a failed to modulate the expression of Fcγ receptors (FcγR) or to otherwise alter the activation threshold. In human mast cells, C5a promoted the production of the neutrophil chemotaxin interleukin-8, and recruitment of neutrophils at 24 hours after serum administration was impaired in C5aR(-/-) mice, suggesting that enhanced neutrophil chemoattractant production underlies the requirement for C5aR on mast cells in arthritis.

CONCLUSION

Stimulation via C5aR is required to unleash the proinflammatory activity of synovial mast cells in immune complex arthritis, albeit via a mechanism that is distinct from C5a-modulated expression of FcγR.

Synovial fibroblasts promote the expression and granule accumulation of tryptase via interleukin-33 and its receptor ST-2 (IL1RL1)

A characteristic feature of tissue resident human mast cells (MCs) is their hTryptase-beta-rich cytoplasmic granules. Mouse MC protease-6 (mMCP-6) is the ortholog of hTryptase-beta, and we have shown that this tetramer-forming tryptase has beneficial roles in innate immunity but adverse roles in inflammatory disorders like experimental arthritis. Because the key tissue factors that control tryptase expression in MCs have not been identified, we investigated the mechanisms by which fibroblasts mediate the expression and granule accumulation of mMCP-6. Immature mouse bone marrow-derived MCs (mBMMCs) co-cultured with fibroblast-like synoviocytes (FLS) or mouse 3T3 fibroblasts markedly increased their levels of mMCP-6. This effect was caused by an undefined soluble factor whose levels could be increased by exposing FLS to tumor necrosis factor-alpha or interleukin (IL)-1beta. Gene expression profiling of mBMMCs and FLS for receptor.ligand pairs of potential relevance raised the possibility that IL-33 was a sought after fibroblast-derived factor that promotes tryptase expression and granule maturation via its receptor IL1RL1/ST2. MCs lacking IL1RL1 exhibited defective fibroblast-driven tryptase accumulation, whereas recombinant IL-33 induced mMCP-6 mRNA and protein accumulation in wild-type mBMMCs. In agreement with these data, synovial MCs from IL1RL1-null mice exhibited a marked reduction in mMCP-6 expression. IL-33 is the first factor shown to modulate tryptase expression in MCs at the mRNA and protein levels. We therefore have identified a novel pathway by which mesenchymal cells exposed to inflammatory cytokines modulate the phenotype of local MCs to shape their immune responses.

Neutrophils in a mouse model of autoantibody-mediated arthritis: critical producers of Fc receptor gamma, the receptor for C5a, and lymphocyte function-associated antigen 1

OBJECTIVE

Neutrophils represent a prominent component of inflammatory joint effusions and are required for synovial inflammation in mouse models, but the mechanisms are poorly understood. In this study, we developed a system with which to test the importance of the production of specific factors by neutrophils in a mouse model of arthritis.

METHODS

Neutrophil-deficient Gfi-1(-/-) mice were administered sublethal doses of radiation and were then engrafted with donor bone marrow cells (BMCs), which resulted in the production of mature neutrophils within 2 weeks. By reconstituting with BMCs from mice lacking selected proinflammatory factors, we generated mice that specifically lacked these factors on their neutrophils. Arthritis was initiated by transfer of K/BxN serum to identify the role of defined neutrophil factors on the incidence and severity of arthritis.

RESULTS

Neutrophils lacking the signaling chain of stimulatory Fc receptors (FcRgamma(-/-)) were unable to elicit arthritis, but neutrophils lacking FcgammaRIII still did so. Neutrophils lacking the chemotactic or adhesion receptor C5a receptor (C5aR) or CD11a/lymphocyte function-associated antigen 1 (LFA-1) also failed to initiate arthritis but could enter joints in which inflammation had been initiated by wild-type neutrophils. Neutrophils unable to produce interleukin-1alpha (IL-1alpha) and IL-1beta (IL-1alpha/beta(-/-)) or leukotrienes (5-lipoxygenase [5-LOX(-/-)]) produced arthritis of intermediate severity. The inability of neutrophils to make tumor necrosis factor or to express receptors for tumor necrosis factor or IL-1 had no effect on arthritis.

CONCLUSION

A novel transfer system was developed to identify neutrophil production of FcRgamma, C5aR, and CD11a/LFA-1 as critical components of autoantibody-mediated arthritis. Neutrophil production of IL-1 and leukotriene B(4) likely contributes to inflammation but is not essential. Molecular requirements for neutrophil influx into joints become more permissive after inflammation is initiated.

Platelets amplify inflammation in arthritis via collagen-dependent microparticle production

In addition to their pivotal role in thrombosis and wound repair, platelets participate in inflammatory responses. We investigated the role of platelets in the autoimmune disease rheumatoid arthritis. We identified platelet microparticles--submicrometer vesicles elaborated by activated platelets--in joint fluid from patients with rheumatoid arthritis and other forms of inflammatory arthritis, but not in joint fluid from patients with osteoarthritis. Platelet microparticles were proinflammatory, eliciting cytokine responses from synovial fibroblasts via interleukin-1. Consistent with these findings, depletion of platelets attenuated murine inflammatory arthritis. Using both pharmacologic and genetic approaches, we identified the collagen receptor glycoprotein VI as a key trigger for platelet microparticle generation in arthritis pathophysiology. Thus, these findings demonstrate a previously unappreciated role for platelets and their activation-induced microparticles in inflammatory joint diseases.

Mast cells contribute to autoimmune inflammatory arthritis via their tryptase/heparin complexes

Although mast cells (MCs) often are abundant in the synovial tissues of patients with rheumatoid arthritis, the contribution of MCs to joint inflammation and cartilage loss remains poorly understood. MC-restricted tryptase/heparin complexes have proinflammatory activity, and significant amounts of human tryptase beta (hTryptase-beta) are present in rheumatoid arthritis synovial fluid. Mouse MC protease-6 (mMCP-6) is the ortholog of hTryptase-beta, and this serine protease is abundant in the synovium of arthritic mice. We now report that C57BL/6 (B6) mice lacking their tryptase/heparin complexes have attenuated arthritic responses, with mMCP-6 as the dominant tryptase responsible for augmenting neutrophil infiltration in the K/BxN mouse serum-transfer arthritis model. While inflammation in this experimental arthritis model was not dependent on protease-activated receptor-2, it was dependent on the chemokine receptor CXCR2. In support of the latter data, exposure of synovial fibroblasts to hTryptase-beta/heparin or mMCP-6/heparin complexes resulted in expression of the neutrophil chemotactic factors CXCL1/KC, CXCL5/LIX, and CXCL8/IL-8. Our proteomics, histochemistry, and immunohistochemistry data also revealed substantial loss of cartilage-derived aggrecan proteoglycans in the arthritic joints of wild-type B6 mice but not mMCP-6-null B6 mice. These observations demonstrate the functional contribution of MC-restricted tryptase/heparin complexes in the K/BxN mouse arthritis model and connect our mouse findings with rheumatoid arthritis pathophysiology.

Genetic inversion in mast cell-deficient (Wsh) mice interrupts corin and manifests as hematopoietic and cardiac aberrancy

Mast cells participate in pathophysiological processes that range from antimicrobial defense to anaphylaxis and inflammatory arthritis. Much of the groundwork for the understanding of mast cells was established in mice that lacked mast cells through defects in either stem cell factor or its receptor, Kit. Among available strains, C57BL/6-Kit(W-sh) (W(sh)) mice are experimentally advantageous because of their background strain and fertility. However, the genetic inversion responsible for the W(sh) phenotype remains poorly defined, and its effects beyond the mast cell have been incompletely characterized. We report that W(sh) animals exhibit splenomegaly with expanded myeloid and megakaryocyte populations. Hematopoietic abnormalities extend to the bone marrow and are reflected by neutrophilia and thrombocytosis. In contrast, mast cell-deficient WBB6F1-Kit(W)/Kit(W-v) (W/W(v)) mice display mild neutropenia, but no changes in circulating platelet numbers. To help define the basis for the W(sh) phenotype, a "DNA walking" strategy was used to identify the precise location of the 3' breakpoint, which was found to reside 67.5 kb upstream of Kit. The 5' breakpoint disrupts corin, a cardiac protease responsible for the activation of atrial natriuretic peptide. Consistent with this result, transcription of full-length corin is ablated and W(sh) mice develop symptoms of cardiomegaly. Studies performed using mast cell-deficient strains must consider the capacity of associated abnormalities to either expose or compensate for the missing mast cell lineage.

Mast Cells in Autoantibody Responses and Arthritis

A pathogenic role for autoantibodies, immune complexes and mast cells has long been hypothesized in rheumatoid arthritis (RA). Recent studies demonstrating novel RA-associated autoantibodies and the efficacy of B cell-directed therapy have led to a renewed interest in the role of humoral immunity in RA. Mouse models of arthritis have provided further support for a direct pathogenic role of autoantibodies in the development of synovial inflammation. Interestingly, in antibody-mediated K/BxN serum transfer arthritis, mast cells have now been identified as a critical cellular mediator of autoantibody-driven joint inflammation. Here, we focus on the role of autoantibodies and mast cells in murine and human inflammatory arthritis.

Predominance of cyclooxygenase 1 over cyclooxygenase 2 in the generation of proinflammatory prostaglandins in autoantibody-driven K/BxN serum-transfer arthritis

OBJECTIVE

Prostaglandins (PGs) are found in high levels in the synovial fluid of patients with rheumatoid arthritis, and nonsteroidal blockade of these bioactive lipids plays a role in patient care. The aim of this study was to explore the relative contribution of cyclooxygenase (COX) isoforms and PG species in the autoantibody-driven K/BxN serum-transfer arthritis.

METHODS

The prostanoid content of arthritic ankles was assessed in ankle homogenates, and the importance of this pathway was confirmed with pharmacologic blockade. The presence of COX isoforms was assessed by Western blotting and their functional contribution was compared using COX-1-/- and COX-2-/- mice as well as isoform-specific inhibitors. The relative importance of PGE2 and PGI2 (prostacyclin) was determined using mice deficient in microsomal PGE synthase 1 (mPGES-1) and in the receptors for PGI2.

RESULTS

High levels of PGE2 and 6-keto-PGF1alpha (a stable metabolite of PGI2) were detected in arthritic joint tissues, correlating strongly with the intensity of synovitis. Pharmacologic inhibition of PG synthesis prevented arthritis and ameliorated active disease. While both COX isoforms were found in inflamed joint tissues, only COX-1 contributed substantially to clinical disease; COX-1-/- mice were fully resistant to disease, whereas COX-2-/- mice remained susceptible. These findings were confirmed by isoform-specific pharmacologic inhibition. Mice lacking mPGES-1 (and therefore PGE2) developed arthritis normally, whereas mice incapable of responding to PGI2 exhibited a significantly attenuated arthritis course, confirming a role of PGI2 in this arthritis model.

CONCLUSION

These findings challenge previous paradigms of distinct "housekeeping" versus inflammatory functions of the COX isoforms and highlight the potential pathogenic contribution of prostanoids synthesized via COX-1, in particular PGI2, to inflammatory arthritis.

Synovial mast cells: role in acute and chronic arthritis

Mast cells reside in the normal synovium and increase strikingly in number in rheumatoid arthritis and other joint diseases. Given the broad spectrum of activity of this lineage, it has for decades been considered probable that mast cells are involved in the pathophysiology of synovitis. Recent work in murine arthritis has substantiated this suspicion, showing that mast cells can contribute importantly to the initiation of inflammatory arthritis. However, the role of the greatly expanded population of synovial mast cells in established arthritis remains unknown. Here we review the current understanding of mast cell function in acute arthritis and consider the potentially important influence of this cell on key processes within the chronically inflamed synovium, including leukocyte recruitment and activation, fibroblast proliferation, angiogenesis, matrix remodeling, and injury to collagen and bone. We also consider recent evidence supporting an immunomodulatory or anti-inflammatory role for mast cells as well as pharmacologic approaches to the mast cell as a therapeutic target in inflammatory arthritis.

Subpopulations within juvenile psoriatic arthritis: a review of the literature

The presentation of juvenile psoriatic arthritis (JPsA) has long been recognized to be clinically heterogeneous. As the definition of JPsA expanded to accommodate atypical manifestations of psoriasis in young children, studies began to reflect an increasingly clear biphasic distribution of age of onset, with peaks in the first few years of life and again in early adolescence. These two subpopulations differ in gender ratio, pattern of joint involvement, laboratory findings and potentially response to therapy. Intriguingly, a similar distribution of age of onset has been observed in juvenile rheumatoid arthritis (JRA), and correlates with patterns of HLA association. While a secure classification of subpopulations within JPsA awaits improved pathophysiologic understanding, future research must consider the possibility that different disease mechanisms may be operative in distinct subsets of patients with this disorder.

Mast cells contribute to initiation of autoantibody-mediated arthritis via IL-1

Mast cells are immune sentinels that participate in the defense against bacteria and parasites. Resident within the joint, mast cells become activated in human rheumatoid arthritis and are implicated in the pathogenesis of experimental murine synovitis. However, their arthritogenic role remains undefined. Using a model of autoantibody-induced arthritis, we show that mast cells contribute to the initiation of inflammation within the joint by elaboration of IL-1. Mast cells become activated to produce this cytokine via the IgG immune complex receptor FcgammaRIII. Interestingly, mast cells become dispensable for the perpetuation of arthritis after delivery of IL-1, highlighting the contribution of this lineage to arthritis induction. These findings illuminate a mechanism by which mast cells can participate in the pathogenesis of autoimmune inflammatory arthritis and provide insights of potential relevance to human rheumatoid arthritis.

Patients with juvenile psoriatic arthritis comprise two distinct populations

OBJECTIVE

Psoriatic arthritis (PsA) in children is clinically heterogeneous. We examined a large population of children with juvenile PsA for evidence of phenotypic clustering that could suggest the presence of distinct clinical entities.

METHODS

We reviewed the medical records of 139 patients meeting the Vancouver criteria for juvenile PsA. To identify segregation into phenotypic groups, we compared younger patients with their older counterparts and subjected the whole population to 2-step cluster analysis.

RESULTS

Among patients with juvenile PsA, the age at onset is biphasic, with peaks occurring at approximately 2 years of age and again in late childhood. Compared with children ages 5 years and older, younger patients are more likely to be female, exhibit dactylitis and small joint involvement, and express antinuclear antibodies. Progression to polyarticular disease (>or=5 joints) is more common in younger children, although joint involvement remains oligoarticular in the majority of children. In contrast, older patents tend to manifest enthesitis, axial joint disease, and persistent oligoarthritis. Uveitis is equally represented in both age groups. Despite a higher utilization of methotrexate therapy, younger patients required, on average, more than twice as long to achieve clinical remission (23 months versus 9.2 months; P = 0.044). Cluster analysis identified largely overlapping subgroups but suggested that the presence of dactylitis, rather than age, has the greatest capacity to predict essential features of the clinical phenotype.

CONCLUSION

Juvenile PsA comprises 2 distinct populations of patients. Although the pathophysiologic correlate of this finding remains undefined, future studies should avoid the assumption that PsA in childhood constitutes a single etiologic entity.

Extreme thrombocytosis predicts Kawasaki disease in infants

Infants with Kawasaki disease are at high risk of developing life-threatening coronary complications, yet may elude timely diagnosis because they often lack the full complement of classic clinical features. We retrospectively studied 26,540 children 1 year of age or less who were evaluated at a tertiary care pediatric emergency department in whom a platelet count was performed. Among those infants with fever without a source identified, 8.5% with platelet counts of 800,000 cells/mm(3) or greater had Kawasaki disease compared to 0.4% with platelet counts of less than 800,000 cells/mm(3) (likelihood ratio for Kawasaki disease was 17 [95% confidence interval, 8-34]). Because many infants present atypically, Kawasaki disease should be considered in all children of 1 year or less with prolonged fever, extreme elevation of the platelet count, and no compelling alternative diagnosis.

Neutrophil-derived leukotriene B4 is required for inflammatory arthritis

Neutrophils serve as a vanguard of the acute innate immune response to invading pathogens. Neutrophils are also abundant at sites of autoimmune inflammation, such as the rheumatoid joint, although their pathophysiologic role is incompletely defined and relevant effector functions remain obscure. Using genetic and pharmacologic approaches in the K/BxN serum transfer model of arthritis, we find that autoantibody-driven erosive synovitis is critically reliant on the generation of leukotrienes, and more specifically on leukotriene B₄ (LTB₄), for disease induction as well as perpetuation. Pursuing the cellular source for this mediator, we find via reconstitution experiments that mast cells are a dispensable source of leukotrienes, whereas arthritis susceptibility can be restored to leukotriene-deficient mice by intravenous administration of wild-type neutrophils. These experiments demonstrate a nonredundant role for LTB₄ in inflammatory arthritis and define a neutrophil mediator involved in orchestrating the synovial eruption.

Particularities of the vasculature can promote the organ specificity of autoimmune attack

How certain autoimmune diseases target specific organs remains obscure. In the 'K/BxN' arthritis model, autoantibodies to a ubiquitous antigen elicit joint-restricted pathology. Here we have used intravital imaging to demonstrate that transfer of arthritogenic antibodies caused macromolecular vasopermeability localized to sites destined to develop arthritis, augmenting its severity. Vasopermeability depended on mast cells, neutrophils and FcgammaRIII but not complement, tumor necrosis factor or interleukin 1. Unexpectedly, radioresistant FcRgamma-expressing cells in an organ distant from the joint were required. Histamine and serotonin were critical, and systemic administration of these vasoactive amines recapitulated the joint localization of immune complex-triggered vasopermeability. We propose that regionally distinct vascular properties 'interface' with immune effector pathways to foster organ-specific autoimmune damage, perhaps explaining why arthritis accompanies many human infectious and autoimmune disorders.

Coronary artery dilation among patients presenting with systemic-onset juvenile idiopathic arthritis

OBJECTIVE

To evaluate coronary artery diameters among patients presenting with systemic-onset juvenile idiopathic arthritis (SoJIA).

METHODS

Fifty cases of SoJIA were reviewed. At the time of initial presentation with fever, 12 patients had echocardiograms that included a complete evaluation of the coronary arteries. A single reviewer measured the diameters of the left main, proximal left anterior descending, and proximal right coronary arteries. Body surface area-adjusted z scores were calculated with respect to a normative population.

RESULTS

Coronary artery dilation (z score: >2) was observed for 5 of the 12 patients with SoJIA who had echocardiograms performed at the time of presentation with fever. No patient developed a coronary artery aneurysm, and all of the coronary artery z scores normalized within 4 months. Only 2 of the 5 patients with coronary artery z scores of >2 fulfilled the clinical criteria for Kawasaki disease, the most commonly recognized cause of coronary artery dilation among children.

CONCLUSIONS

Children presenting with SoJIA may have coronary artery dilation similar to that observed for children with Kawasaki disease. These data suggest that the presence of coronary artery dilation on initial echocardiograms for patients with fever does not exclude the diagnosis of SoJIA.

Mast cells in inflammatory arthritis

Mast cells are present in limited numbers in normal human synovium, but in rheumatoid arthritis and other inflammatory joint diseases this population can expand to constitute 5% or more of all synovial cells. Recent investigations in a murine model have demonstrated that mast cells can have a critical role in the generation of inflammation within the joint. This finding highlights the results of more than 20 years of research indicating that mast cells are frequent participants in non-allergic immune responses as well as in allergy. Equipped with a diversity of surface receptors and effector capabilities, mast cells are sentinels of the immune system, detecting and delivering a first response to invading bacteria and other insults. Accumulating within inflamed tissues, mast cells produce cytokines and other mediators that may contribute vitally to ongoing inflammation. Here we review some of the non-allergic functions of mast cells and focus on the potential role of these cells in murine and human inflammatory arthritis.

Raynaud's phenomenon in children: a retrospective review of 123 patients

OBJECTIVE

To examine the clinical presentation and disease associations of Raynaud's phenomenon (RP) in children and adolescents.

METHODS

A systematic retrospective chart review was conducted of 123 cases drawn from 2 computerized databases at the Children's Hospital of Boston. Participants aged <19 years with episodic reversible color changes in the extremities were examined. Case records were analyzed for clinical presentation, disease associations, and physical examination and laboratory findings.

RESULTS

In contrast to the findings of smaller pediatric series reported to date, the large majority of our patients-approximately 70%-did not have a recognized underlying connective tissue disease. For both primary and secondary RP, approximately 80% of patients were female, and mean age of onset was similar in the 2 groups. Biphasic or triphasic color changes were less common than monophasic changes and were no more common in secondary than primary RP. Findings predictive of secondary RP were limited to the presence of antinuclear antibodies and abnormal nailfold capillaries. Antiphospholipid antibodies were found at some time in at least 21% of patients with both primary and secondary RP.

CONCLUSIONS

RP in children, as in adults, principally affects girls and is frequently free of association with connective tissue disease. Antinuclear antibody positivity and abnormal nailfold capillaries correlate with secondary disease. Antiphospholipid antibodies are surprisingly common, a new finding of uncertain implications.