A heterozygous RAB27A mutation causes delayed cytolytic granule polarization and hemophagocytic lymphohistiocytosis in 2 unrelated teenagers

Frequently fatal, primary hemophagocytic lymphohistiocytosis (HLH) occurs in infancy resulting from homozygous mutations in natural killer (NK) and CD8 T cell cytolytic pathway genes. Secondary HLH presents after infancy and may be associated with heterozygous mutations in HLH genes. We report 2 unrelated teenagers with HLH and an identical heterozygous RAB27A mutation (259 G>C). The contribution of this Rab27A missense (A87P) mutation on NK cell cytotoxicity was studied by cloning it into a lentiviral expression vector prior to introduction into the human NK-92 cell line. NK cell degranulation (CD107a expression), target cell conjugation, and K562 target cell lysis was compared between mutant and wild-type (WT) transduced NK-92 cells. Polarization of granzyme B to the immunologic synapse and interaction of mutant Rab27A (A87P) with Munc13-4 were explored by confocal microscopy and proximity ligation assay (PLA), respectively. Over-expression of the RAB27A mutation had no effect on cell conjugate formation between the NK and target cells but decreased NK cell cytolytic activity and degranulation. Moreover, the mutant Rab27A protein was predicted to disrupt binding to WT Munc13-4 by crystal structure modelling, and decreased interaction of Rab27A (A87P) with WT Munc13-4 was shown by PLA in situ and by co-immunoprecipiation in vitro. Finally, Rab27A (A87P) over-expression in NK-92 cells delayed granzyme B polarization toward the immunologic synapse, as noted by confocal microscopy, with a resulting increase in interferon-γ production, a cytokine responsible for HLH. This heterozygous RAB27A mutation blurs the genetic distinction between primary and secondary HLH by contributing to HLH via a partial dominant-negative effect.

Macrophage activation syndrome in the era of biologic therapy

Macrophage activation syndrome (MAS) refers to acute overwhelming inflammation caused by a 'cytokine storm'. Although increasingly recognized as a life-threatening complication of various rheumatic diseases, clinically, MAS is strikingly similar to primary and secondary forms of haemophagocytic lymphohistiocytosis (HLH). Not surprisingly, many rheumatologists prefer the term secondary HLH rather than MAS to describe this condition, and efforts to change the nomenclature are in progress. The pathophysiology of MAS remains elusive, but observations in animal models, as well as data on the effects of new anticytokine therapies on rates and clinical presentations of MAS in patients with systemic juvenile idiopathic arthritis (sJIA), provide clues to the understanding of this perplexing clinical phenomenon. In this Review, we explore the latest available evidence and discuss potential diagnostic challenges in the era of increasing use of biologic therapies.

Whole-Exome Sequencing Reveals Mutations in Genes Linked to Hemophagocytic Lymphohistiocytosis and Macrophage Activation Syndrome in Fatal Cases of H1N1 Influenza

BACKGROUND

Severe H1N1 influenza can be lethal in otherwise healthy individuals and can have features of reactive hemophagocytic lymphohistiocytosis (HLH). HLH is associated with mutations in lymphocyte cytolytic pathway genes, which have not been previously explored in H1N1 influenza.

METHODS

Sixteen cases of fatal influenza A(H1N1) infection, 81% with histopathologic hemophagocytosis, were identified and analyzed for clinical and laboratory features of HLH, using modified HLH-2004 and macrophage activation syndrome (MAS) criteria. Fourteen specimens were subject to whole-exome sequencing. Sequence alignment and variant filtering detected HLH gene mutations and potential disease-causing variants. Cytolytic function of the PRF1 p.A91V mutation was tested in lentiviral-transduced NK-92 natural killer (NK) cells.

RESULTS

Despite several lacking variables, cases of influenza A(H1N1) infection met 44% and 81% of modified HLH-2004 and MAS criteria, respectively. Five subjects (36%) carried one of 3 heterozygous LYST mutations, 2 of whom also possessed the p.A91V PRF1 mutation, which was shown to decrease NK cell cytolytic function. Several patients also carried rare variants in other genes previously observed in MAS.

CONCLUSIONS

This cohort of fatal influenza A(H1N1) infections confirms the presence of hemophagocytosis and HLH pathology. Moreover, the high percentage of HLH gene mutations suggests they are risk factors for mortality among individuals with influenza A(H1N1) infection.

A Heterozygous RAB27A Mutation Associated with Delayed Cytolytic Granule Polarization and Hemophagocytic Lymphohistiocytosis

Frequently fatal, primary hemophagocytic lymphohistiocytosis (HLH) occurs in infancy resulting from homozygous mutations in NK and CD8 T cell cytolytic pathway genes. Secondary HLH presents after infancy and may be associated with heterozygous mutations in HLH genes. We report two unrelated teenagers with HLH and an identical heterozygous RAB27A mutation (c.259G→C). We explore the contribution of this Rab27A missense (p.A87P) mutation on NK cell cytolytic function by cloning it into a lentiviral expression vector prior to introduction into the human NK-92 cell line. NK cell degranulation (CD107a expression), target cell conjugation, and K562 target cell lysis was compared between mutant- and wild-type-transduced NK-92 cells. Polarization of granzyme B to the immunologic synapse and interaction of mutant Rab27A (p.A87P) with Munc13-4 were explored by confocal microscopy and proximity ligation assay, respectively. Overexpression of the RAB27A mutation had no effect on cell conjugate formation between the NK and target cells but decreased NK cell cytolytic activity and degranulation. Moreover, the mutant Rab27A protein decreased binding to Munc13-4 and delayed granzyme B polarization toward the immunologic synapse. This heterozygous RAB27A mutation blurs the genetic distinction between primary and secondary HLH by contributing to HLH via a partial dominant-negative effect.

2016 Classification Criteria for Macrophage Activation Syndrome Complicating Systemic Juvenile Idiopathic Arthritis: A European League Against Rheumatism/American College of Rheumatology/Paediatric Rheumatology International Trials Organisation Collaborative Initiative

OBJECTIVE

To develop criteria for the classification of macrophage activation syndrome (MAS) in patients with systemic juvenile idiopathic arthritis (JIA).

METHODS

A multistep process, based on a combination of expert consensus and analysis of real patient data, was conducted. A panel of 28 experts was first asked to classify 428 patient profiles as having or not having MAS, based on clinical and laboratory features at the time of disease onset. The 428 profiles comprised 161 patients with systemic JIA-associated MAS and 267 patients with a condition that could potentially be confused with MAS (active systemic JIA without evidence of MAS, or systemic infection). Next, the ability of candidate criteria to classify individual patients as having MAS or not having MAS was assessed by evaluating the agreement between the classification yielded using the criteria and the consensus classification of the experts. The final criteria were selected in a consensus conference.

RESULTS

Experts achieved consensus on the classification of 391 of the 428 patient profiles (91.4%). A total of 982 candidate criteria were tested statistically. The 37 best-performing criteria and 8 criteria obtained from the literature were evaluated at the consensus conference. During the conference, 82% consensus among experts was reached on the final MAS classification criteria. In validation analyses, these criteria had a sensitivity of 0.73 and a specificity of 0.99. Agreement between the classification (MAS or not MAS) obtained using the criteria and the original diagnosis made by the treating physician was high (κ = 0.76).

CONCLUSION

We have developed a set of classification criteria for MAS complicating systemic JIA and provided preliminary evidence of its validity. Use of these criteria will potentially improve understanding of MAS in systemic JIA and enhance efforts to discover effective therapies, by ensuring appropriate patient enrollment in studies.

Expert consensus on dynamics of laboratory tests for diagnosis of macrophage activation syndrome complicating systemic juvenile idiopathic arthritis

OBJECTIVE

To identify which laboratory tests that change over time are most valuable for the timely diagnosis of macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (sJIA).

METHODS

A multistep process, based on a combination of expert consensus and analysis of real patient data, was conducted. A panel of experts was first asked to evaluate 115 profiles of patients with MAS, which included the values of laboratory tests at the pre-MAS visit and at MAS onset, and the change in values between the two time points. The experts were asked to choose the 5 laboratory tests in which change was most important for the diagnosis of MAS and to rank the 5 selected tests in order of importance. The relevance of change in laboratory parameters was further discussed and ranked by the same experts at a consensus conference.

RESULTS

Platelet count was the most frequently selected test, followed by ferritin level, aspartate aminotransferase (AST), white cell count, neutrophil count, and fibrinogen and erythrocyte sedimentation rate. Ferritin was most frequently assigned the highest score. At the end of the process, platelet count, ferritin level and AST were the laboratory tests in which the experts found change over time to be most important.

CONCLUSIONS

We identified the laboratory tests in which change over time is most valuable for the early diagnosis of MAS in sJIA. The dynamics of laboratory values during the course of MAS should be further scrutinised in a prospective study in order to establish the optimal cut-off values for their variation.

Whole-exome sequencing reveals overlap between macrophage activation syndrome in systemic juvenile idiopathic arthritis and familial hemophagocytic lymphohistiocytosis

OBJECTIVE

Macrophage activation syndrome (MAS), a life-threatening complication of systemic juvenile idiopathic arthritis (JIA), resembles familial hemophagocytic lymphohistiocytosis (HLH), a constellation of autosomal-recessive immune disorders resulting from deficiency in cytolytic pathway proteins. We undertook this study to test our hypothesis that MAS predisposition in systemic JIA could be attributed to rare gene sequence variants affecting the cytotolytic pathway.

METHODS

Whole-exome sequencing was used in 14 patients with systemic JIA and MAS and in their parents to identify protein-altering single-nucleotide polymorphisms/indels in known HLH-associated genes. To discover new candidate genes, the entire whole-exome sequencing data were filtered to identify protein-altering, rare recessive homozygous, compound heterozygous, and de novo variants with the potential to affect the cytolytic pathway.

RESULTS

Heterozygous protein-altering rare variants in the known genes (LYST,MUNC13-4, and STXBP2) were found in 5 of 14 patients with systemic JIA and MAS (35.7%). This was in contrast to only 4 variants in 4 of 29 patients with systemic JIA without MAS (13.8%). Homozygosity and compound heterozygosity analysis applied to the entire whole-exome sequencing data in systemic JIA/MAS revealed 3 recessive pairs in 3 genes and compound heterozygotes in 73 genes. We also identified 20 heterozygous rare protein-altering variants that occurred in at least 2 patients. Many of the identified genes encoded proteins with a role in actin and microtubule reorganization and vesicle-mediated transport. "Cellular assembly and organization" was the top cellular function category based on Ingenuity Pathways Analysis (P < 3.10 × 10(-5) ).

CONCLUSION

Whole-exome sequencing performed in patients with systemic JIA and MAS identified rare protein-altering variants in known HLH-associated genes as well as in new candidate genes.

Pathogenesis of macrophage activation syndrome and potential for cytokine- directed therapies

Macrophage activation syndrome (MAS) is an acute episode of overwhelming inflammation characterized by activation and expansion of T lymphocytes and hemophagocytic macrophages. In rheumatology, it occurs most frequently in patients with systemic juvenile idiopathic arthritis (SJIA) and systemic lupus erythematosus. The main clinical manifestations include cytopenias, liver dysfunction, coagulopathy resembling disseminated intravascular coagulation, and extreme hyperferritinemia. Clinically and pathologically, MAS bears strong similarity to hemophagocytic lymphohistiocytosis (HLH), and some authors prefer the term secondary HLH to describe it. Central to its pathogenesis is a cytokine storm, with markedly increased levels of numerous proinflammatory cytokines including IL-1, IL-6, IL-18, TNFα, and IFNγ. Although there is evidence that IFNγ may play a central role in the pathogenesis of MAS, the role of other cytokines is still not clear. There are several reports of SJIA-associated MAS dramatically benefiting from anakinra, a recombinant IL-1 receptor antagonist, but the utility of other biologics in MAS is not clear. The mainstay of treatment remains corticosteroids; other medications, including cyclosporine, are used in patients who fail to respond.

Macrophage activation syndrome and cytokine-directed therapies

Macrophage activation syndrome (MAS) is an episode of overwhelming inflammation that occurs most commonly in children with systemic juvenile idiopathic arthritis (SJIA). It is characterized by expansion and activation of T lymphocytes and hemophagocytic macrophages and bears great similarity to hemophagocytic lymphohistiocytosis (HLH). This disorder has substantial morbidity and mortality, and there is frequently a delay in recognition and initiation of treatment. Here, we will review what is known about the pathogenesis of MAS and, in particular, its similarities to HLH. The development of MAS is characterized by a cytokine storm, with the elaboration of numerous pro-inflammatory cytokines. We will examine the evidence for various cytokines in the initiation and pathogenesis of MAS and discuss how new biologic therapies may alter the risk of MAS. Finally, we will review current treatment options for MAS and examine how cytokine-directed therapy could serve as novel treatment modalities.

Follistatin-like protein 1 and the ferritin/erythrocyte sedimentation rate ratio are potential biomarkers for dysregulated gene expression and macrophage activation syndrome in systemic juvenile idiopathic arthritis

OBJECTIVE

Follistatin-like protein 1 (FSTL-1) is a secreted glycoprotein overexpressed in certain inflammatory diseases. Our objective was to correlate FSTL-1 levels with gene expression, known biomarkers, and measures of disease activity in systemic juvenile idiopathic arthritis (sJIA), including macrophage activation syndrome (MAS).

METHODS

FSTL-1 serum levels were measured by ELISA in 28 patients with sJIA, including 7 patients who developed MAS, and 30 healthy controls. Levels were correlated with erythrocyte sedimentation rate (ESR), ferritin, and soluble interleukin-2 receptor-α (sIL-2Rα). Gene expression based on FSTL-1 levels was analyzed in peripheral blood mononuclear cells (PBMC).

RESULTS

Serum levels of FSTL-1 were elevated at time of presentation of sJIA (mean 200.7 ng/ml) and decreased to normal (mean 133.7 ng/ml) over 24 months (p < 0.01). FSTL-1 levels were markedly elevated during acute MAS (mean 279.8 ng/ml) and decreased to normal following treatment (p < 0.001). FSTL-1 levels correlated with serum markers of inflammation, including sIL-2Rα and ferritin. Ferritin/ESR ratio was superior to ferritin, sIL-2Rα, and FSTL-1 in discriminating MAS from new-onset sJIA. PBMC from patients with FSTL-1 levels > 200 ng/ml showed altered expression of genes related to innate immunity, erythropoiesis, and natural killer cell dysfunction. Two patients with the highest FSTL-1 levels at disease onset (> 300 ng/ml) ultimately developed MAS.

CONCLUSION

Elevated pretreatment serum FSTL-1 levels in sJIA are associated with dysregulated gene expression suggestive of occult MAS, and may have utility in predicting progression to overt MAS. Ferritin/ESR ratio may be superior to ferritin alone in discriminating overt MAS from new-onset sJIA.

The limited role of interferon-γ in systemic juvenile idiopathic arthritis cannot be explained by cellular hyporesponsiveness

OBJECTIVE

Systemic juvenile idiopathic arthritis (JIA) is an autoinflammatory syndrome in which the myelomonocytic lineage appears to play a pivotal role. Inflammatory macrophages are driven by interferon-γ (IFNγ), but studies have failed to demonstrate an IFN- induced gene signature in active systemic JIA. This study sought to characterize the status of an IFN-induced signature within affected tissue and to gauge the integrity of IFN signaling pathways within peripheral monocytes from patients with systemic JIA.

METHODS

Synovial tissue from 12 patients with active systemic JIA and 9 with active extended oligoarticular JIA was assessed by real-time polymerase chain reaction to quantify IFN-induced chemokine gene expression. Peripheral monocytes from 3 patients with inactive systemic JIA receiving anti-interleukin-1β (anti-IL-1β) therapy, 5 patients with active systemic JIA, and 8 healthy controls were incubated with or without IFNγ to gauge changes in gene expression and to measure phosphorylated STAT-1 (pSTAT-1) levels.

RESULTS

IFN-induced chemokine gene expression in synovium was constrained in active systemic JIA compared to the known IFN-mediated extended oligoarticular subtype. In unstimulated peripheral monocytes, IFN-induced gene expression was similar between the groups, except that lower levels of STAT1, MIG, and PIAS were observed in patients with active disease, while higher levels of PIAS1 were observed in patients with inactive disease. Basal pSTAT-1 levels in monocytes tended to be higher in systemic JIA patients compared to healthy controls, with the highest levels seen in those with inactive disease. Upon stimulation of monocytes, the fold increase in gene expression was roughly equal between groups, except for a greater increase in STAT1 in patients with inactive systemic JIA compared to controls, and a greater increase in IRF1 in those with active compared to inactive disease. Upon stimulation, the fold increase in pSTAT-1 was highest in monocytes from patients with inactive systemic JIA.

CONCLUSION

Monocytes in patients with active systemic JIA retain the ability to respond to IFNγ, suggesting that the lack of an IFN-induced gene signature in patients with active disease reflects a limited in vivo exposure to IFNγ. In patients with inactive systemic JIA who received treatment with anti-IL-1β, hyperresponsiveness to IFNγ was observed.

Macrophage activation syndrome as part of systemic juvenile idiopathic arthritis: diagnosis, genetics, pathophysiology and treatment

Macrophage activation syndrome (MAS) is a severe, frequently fatal complication of systemic juvenile idiopathic arthritis (sJIA) with features of hemophagocytosis leading to coagulopathy, pancytopenia, and liver and central nervous system dysfunction. MAS is overt in 10% of children with sJIA but occurs subclinically in another 30-40%. It is difficult to distinguish sJIA disease flare from MAS. Development of criteria for establishing MAS as part of sJIA are under way and will hopefully prove sensitive and specific. Mutations in cytolytic pathway genes are increasingly being recognized in children who develop MAS as part of sJIA. Identification of these mutations may someday assist in MAS diagnosis. Defects in cytolytic genes have provided murine models of MAS to study pathophysiology and treatment. Recently, the first mouse model of MAS not requiring infection but rather dependent on repeated stimulation through Toll-like receptors was reported. This provides a model of MAS that may more accurately reflect MAS pathology in the setting of autoinflammation or autoimmunity. This model confirms the importance of a balance between pro- and anti-inflammatory cytokines. There has been remarkable progress in the use of anti-pro-inflammatory cytokine therapy, particularly against interleukin-1, in the treatment of secondary forms of MAS, such as in sJIA.

Biologic similarities based on age at onset in oligoarticular and polyarticular subtypes of juvenile idiopathic arthritis

OBJECTIVE

To explore biologic correlates to age at onset in patients with juvenile idiopathic arthritis (JIA) using peripheral blood mononuclear cell (PBMC) gene expression analysis.

METHODS

PBMCs were isolated from 56 healthy controls and 104 patients with recent-onset JIA (39 with persistent oligoarticular JIA, 45 with rheumatoid factor-negative polyarticular JIA, and 20 with systemic JIA). RNA was amplified and labeled using NuGEN Ovation, and gene expression was assessed with Affymetrix HG-U133 Plus 2.0 GeneChips.

RESULTS

A total of 832 probe sets revealed gene expression differences (false discovery rate 5%) in PBMCs from children with oligoarticular JIA whose disease began before age 6 years (early-onset disease) compared with those whose disease began at or after age 6 years (late-onset disease). In patients with early-onset disease, there was greater expression of genes related to B cells and less expression of genes related to cells of the myeloid lineage. Support vector machine analyses identified samples from patients with early- or late-onset oligoarticular JIA (with 97% accuracy) or from patients with early- or late-onset polyarticular JIA (with 89% accuracy), but not from patients with systemic JIA or healthy controls. Principal components analysis showed that age at onset was the major classifier of samples from patients with oligoarticular JIA and patients with polyarticular JIA.

CONCLUSION

PBMC gene expression analysis reveals biologic differences between patients with early-and late-onset JIA, independent of classification based on the number of joints involved. These data suggest that age at onset may be an important parameter to consider in JIA classification. Furthermore, pathologic mechanisms may vary with age at onset, and understanding these processes may lead to improved treatment of JIA.

Gene Expression Profiles from Peripheral Blood Mononuclear Cells Are Sensitive to Short Processing Delays

In the analysis of peripheral blood gene expression, timely processing of samples is essential to ensure that measurements reflect in vivo biology, rather than ex vivo sample processing variables. The effect of processing delays on global gene expression patterns in peripheral blood mononuclear cells (PBMCs) was assessed by isolating and stabilizing PBMC-derived RNA from 3 individuals either immediately after phlebotomy or after a 4 h delay. RNA was labeled using NuGEN Ovation labeling and probed using the Affymetrix HG U133 Plus 2.0 GeneChip(®). Comparison of gene expression levels (≥2-fold expression change and P < 0.05) identified 307 probe sets representing genes with increased expression and 46 indicating decreased expression after 4 h. These differentially expressed genes include many that are important to inflammatory, immunologic, and cancer pathways. Among others, CCR2, CCR5, TLR10, CD180, and IL-16 have decreased expression, whereas VEGF, IL8, SOCS2, SOCS3, CD69, and CD83 have increased expression after a 4 h processing delay. The trends in expression patterns associated with delayed processing were also apparent in an independent set of 276 arrays of RNA from human PBMC samples with varying processing times. These data indicate that the time between sample acquisition, initiation of processing, and when the RNA is stabilized should be a prime consideration when designing protocols for translational studies involving PBMC gene expression analysis.

Macrophage activation syndrome: advances towards understanding pathogenesis

PURPOSE OF REVIEW

Macrophage activation syndrome (MAS), a major cause of morbidity and mortality in pediatric rheumatology, is most strongly associated with systemic juvenile idiopathic arthritis (SJIA). There are no validated diagnostic criteria and early diagnosis is difficult. This review summarizes the progress in understanding of MAS pathophysiology that may help define specific diagnostic biomarkers.

RECENT FINDINGS

MAS is similar to the autosomal recessive disorders collectively known as familial hemophagocytic lymphohistiocytosis (FHLH), all associated with various genetic defects affecting the cytolytic pathway. Cytolytic function is profoundly depressed in SJIA with MAS as well. This immunologic abnormality distinguishes SJIA from other rheumatic diseases and is caused by both genetic and acquired factors. Phenotypic characterization of hemophagocytic macrophages has been another focus of research. These macrophages express CD163, a scavenger receptor that binds hemoglobin-haptoglobin complexes, and initiate pathways important for adaptation to oxidative stress induced by free iron. Expansion of these macrophages is seen in more than 30% of SJIA patients perhaps representing early stages of MAS. Recent gene expression studies linked expansion of these macrophages to distinct signatures.

SUMMARY

Recent advances in understanding of pathophysiologic conditions that favor expansion of hemophagocytic macrophages provide a source of new MAS biomarkers with applicability to clinical practice.

Macrophage activation syndrome in patients with systemic juvenile idiopathic arthritis is associated with MUNC13-4 polymorphisms

OBJECTIVE

Systemic juvenile idiopathic arthritis (JIA) is associated with macrophage activation syndrome. Macrophage activation syndrome bears a close resemblance to familial hemophagocytic lymphohistiocytosis (HLH). The development of familial HLH has been recently associated with mutations in MUNC13-4. The purpose of this study was to assess for possible sequence alterations in MUNC13-4 in patients with systemic JIA/macrophage activation syndrome.

METHODS

The MUNC13-4 sequence was analyzed in 18 unrelated patients with systemic JIA/macrophage activation syndrome, using 32 primer pair sets designed to amplify the 32 exons and at least 100 basepairs of the adjacent intronic regions. DNA samples obtained from 73 unrelated patients with systemic JIA and no history of macrophage activation syndrome and 229 unrelated healthy individuals were used as controls.

RESULTS

The biallelic sequence variants in MUNC13-4 reported in familial HLH were present in 2 of the 18 patients with JIA/macrophage activation syndrome. Further analysis of the MUNC13-4 sequences revealed an identical combination of 12 single-nucleotide polymorphisms (SNPs) in 9 of the remaining 16 patients with systemic JIA/macrophage activation syndrome (56%). Additional analysis suggested that these 12 SNPs (154[-19] g>a, 261[+26] c>g, 388[+81] g>a, 388[+122] c>t, 570[-60] t>g, 888 G>C, 1389[+36] g>a, 1992[+5] g>a, 2447[+144] c>t, 2599 A>G, 2830[+37] c>g, 3198 A>G) were inherited as an extended haplotype. In several patients, in addition to the described haplotype, there were other SNPs in the second allele of MUNC13-4. Moreover, 1 patient had a complex mutation with 2 changes, 2542 A>C and 2943 G>C, in a cis configuration. The haplotype was present in only 27 (12%) of 229 healthy control subjects (chi(2) = 23.5) and in 6 (8.2%) of 73 patients with systemic JIA and no history of macrophage activation syndrome.

CONCLUSION

The data suggest an association between MUNC13-4 polymorphisms and macrophage activation syndrome in patients with systemic JIA.

Systemic JIA: new developments in the understanding of the pathophysiology and therapy

Systemic juvenile idiopathic arthritis (sJIA) is a rare, systemic inflammatory disease classified as a subtype of JIA. Besides arthritis, it is characterised by systemic features such as spiking fever, skin rash, hepatosplenomegaly or serositis. It is becoming clear now that abnormalities in the innate immunity (cytokines such as interleukin (IL)-1, IL-6 and IL-18, and neutrophils and monocytes/macrophages rather than lymphocytes) play a major role in the pathogenesis of sJIA, distinguishing it from other JIA subtypes. Another distinctive feature of sJIA is its strong association with macrophage activation syndrome (MAS). Based on this, consensus is emerging that sJIA should be viewed as an autoinflammatory syndrome rather than a classic auto-immune disease. As a consequence of the progression in understanding the underlying mechanisms of sJIA, major changes in the management are evolving. So far, treatment has been based on glucocorticosteroids in combination with disease-modifying drugs such as methotrexate. Recently, remarkable improvement has been observed with IL-1 and IL-6 targeted therapies. These therapies might also change the long-term outcome of this disease. However, controlled trials set up in international collaboration are needed to determine the optimal treatment strategies for all sJIA patients.

Gene expression signatures in polyarticular juvenile idiopathic arthritis demonstrate disease heterogeneity and offer a molecular classification of disease subsets

OBJECTIVE

To determine whether peripheral blood mononuclear cells (PBMCs) from children with recent-onset polyarticular juvenile idiopathic arthritis (JIA) exhibit biologically or clinically informative gene expression signatures.

METHODS

Peripheral blood samples were obtained from 59 healthy children and 61 children with polyarticular JIA prior to treatment with second-line medications, such as methotrexate or biologic agents. RNA was extracted from isolated mononuclear cells, fluorescence labeled, and hybridized to commercial gene expression microarrays (Affymetrix HG-U133 Plus 2.0). Data were analyzed using analysis of variance at a 5% false discovery rate threshold after robust multichip analysis preprocessing and distance-weighted discrimination normalization.

RESULTS

Initial analysis revealed 873 probe sets for genes that were differentially expressed between polyarticular JIA patients and healthy controls. Hierarchical clustering of these probe sets distinguished 3 subgroups within the polyarticular JIA group. Prototypical patients within each subgroup were identified and used to define subgroup-specific gene expression signatures. One of these signatures was associated with monocyte markers, another with transforming growth factor beta-inducible genes, and a third with immediate early genes. Correlation of gene expression signatures with clinical and biologic features of JIA subgroups suggested relevance to aspects of disease activity and supported the division of polyarticular JIA into distinct subsets.

CONCLUSION

Gene expression signatures in PBMCs from patients with recent-onset polyarticular JIA reflect discrete disease processes and offer a molecular classification of disease.