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

Reaching the Threshold: A Multilayer Pathogenesis of Macrophage Activation Syndrome

Macrophage activation syndrome (MAS) is a potentially fatal complication of rheumatic diseases. The condition is considered part of secondary hemophagocytic lymphohistiocytoses (HLH). There are similarities in genetic background, pathogenesis, and clinical and laboratory features with primary HLH (p-HLH). We describe findings in mouse models of secondary HLH, comparing them with models of p-HLH and the cellular and molecular mechanisms involved, and relate them to recent findings in patients with secondary HLH. A multilayer model is presented in which background inflammation, infections, and genetics all contribute in different proportions and in several ways. Once the “threshold” has been reached, inflammatory cytokines are the final effectors, independent of the interplay between different upstream pathogenic factors.

Monogenic causes of inflammatory disease in rheumatology

PURPOSE OF REVIEW

To review the single-gene defects that can mimic rheumatologic diseases.

RECENT FINDINGS

Monogenic disorders can cause a variety of diseases that may be seen by a rheumatologist. Many of these illnesses present with recurrent episodes of arthritis, rash, fever and inflammation, and serositis. Recent discoveries have defined inflammatory diseases due to mutations in the IL-1 and IL-36 receptor antagonists, as well as the immunoproteosome. Further study of well defined monogenic causes of inflammatory diseases, such as FMF, PAPA, TRAPS, and HIDS, has elucidated the pathophysiology of these diseases leading to targeted immunotherapy with anticytokine biological medications.

SUMMARY

A rheumatologist should be aware of the genetic causes of inflammatory disease mimics. This will not only help with the prognosis of these diseases, but also help to guide therapy to prevent long-term complications associated with these disorders.

Treatment of hemophagocytic lymphohistiocytosis with alemtuzumab in systemic lupus erythematosus

Hemophagocytic lymphohistiocytosis (HLH) is an immune disorder characterized by cytokine dysregulation and uncontrolled activation of T lymphocytes and macrophages. It is categorized as primary when associated with specific genetic mutations or secondary when associated with infections, malignancies, or autoimmune disorders. Clinical features of HLH include unexplained fever, hepatosplenomegaly, pancytopenia, and severe hyperferritinemia. Treatment of primary HLH has become standardized based on the HLH-2004 protocol using cyclosporine, etoposide, and dexamethasone with or without intrathecal methotrexate followed by hematopoietic stem cell transplantation. Treatment of secondary HLH is directed at control of the underlying condition. If unsuccessful, cytotoxic agents such as those in HLH-2004, steroids, intravenous γ-globulin, or targeted immune therapy have been used. Immunotherapy targeting CD52 expressed on immune effector cells of HLH is a rational therapeutic approach in patients too ill for traditional cytotoxic chemotherapy. We describe the successful use of alemtuzumab to treat HLH due to systemic lupus erythematosus.

Protection from inflammatory organ damage in a murine model of hemophagocytic lymphohistiocytosis using treatment with IL-18 binding protein

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition due to the association of an infectious agent with lymphocyte cytotoxicity defects, either of congenital genetic origin in children or presumably acquired in adults. In HLH patients, an excess of lymphocyte or macrophage cytokines, such as IFN-γ and TNFα is present in serum. In animal models of the disease, IFN-γ and TNF-α have been shown to play a central pathogenic role. In humans, unusually high concentrations of IL-18, an inducer of IFN-γ, and TNF-α have been reported, and are associated with an imbalance between IL-18 and its natural inhibitor IL-18 binding protein (IL-18BP) resulting in an excess of free IL-18. Here we studied whether IL-18BP could reduce disease severity in an animal model of HLH. Mouse cytomegalovirus infection in perforin-1 knock-out mice induced a lethal condition similar to human HLH characterized by cytopenia with marked inflammatory lesions in the liver and spleen as well as the presence of hemophagocytosis in bone marrow. IL-18BP treatment decreased hemophagocytosis and reversed liver as well as spleen damage. IL-18BP treatment also reduced both IFN-γ and TNF-α production by CD8(+) T and NK cells, as well as Fas ligand expression on NK cell surface. These data suggest that IL-18BP is beneficial in an animal model of HLH and in combination with anti-infectious therapy may be a promising strategy to treat HLH patients.

Treating inflammation by blocking interleukin-1 in a broad spectrum of diseases

Interleukin-1 (IL-1) is a highly active pro-inflammatory cytokine that lowers pain thresholds and damages tissues. Monotherapy blocking IL-1 activity in autoinflammatory syndromes results in a rapid and sustained reduction in disease severity, including reversal of inflammation-mediated loss of sight, hearing and organ function. This approach can therefore be effective in treating common conditions such as post-infarction heart failure, and trials targeting a broad spectrum of new indications are underway. So far, three IL-1-targeted agents have been approved: the IL-1 receptor antagonist anakinra, the soluble decoy receptor rilonacept and the neutralizing monoclonal anti-IL-1β antibody canakinumab. In addition, a monoclonal antibody directed against the IL-1 receptor and a neutralizing anti-IL-1α antibody are in clinical trials.

Clinical analysis of macrophage activation syndrome in pediatric patients with autoimmune diseases

Macrophage activation syndrome (MAS) belongs to secondary hemophagocytic lymphohistiocytosis (HLH) syndrome. It is usually associated with rheumatic diseases. We retrospectively reviewed our hospital's medical records of 102 HLH/MAS patients from the past 20 years. Demographics, clinical data, treatment, and outcomes were analyzed. Among 102 patients, eight patients with underlying juvenile systemic lupus erythematous (two patients), mixed connective tissue disease (one patient), primary anti-phospholipid syndrome (one patient), and systemic type juvenile rheumatoid arthritis (sJRA; four patients) with 13 episodes of MAS were studied. Clinical manifestations of MAS included fever (100 %), hepatosplenomegaly (77 %), lymphadenopathy (38 %), skin rash (62 %), and neurological involvement (31 %). Laboratory features included leukopenia (54 %), anemia (46 %), thrombocytopenia (77 %), jaundice (27 %), hypofibrinogenemia (40 %), decreased erythrocyte sedimentation rate (67 %), and elevated liver enzymes (77 %), lactate dehydrogenase (100 %), ferritin (88 %), triglycerides (91 %), C-reactive protein (85 %), plasma D-dimer (50 %), and hemophagocytosis in bone marrow (83 %). The Epstein-Barr virus and adenovirus infection triggered MAS in two patients with sJRA. Methylprednisolone pulse therapy was effective in two out of three patients, and high-dose intravenous immunoglobulin (IVIG) was effective in two out of six patients. Patients with sJRA responded well to corticosteroids and cyclosporine. Complications included opportunistic infection with Pneumocystis jiroveci, multiple organ failure, and intensive care unit myopathy. The mortality rate was one out of eight (12.5 %). Our results showed that MAS could be fatal and complicate various pediatric autoimmune diseases. It generally has a good response to corticosteroids and IVIG. Prompt recognition and timely treatment can result in good outcomes.

Familial and acquired hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome in which an uncontrolled and ineffective immune response, triggered in most cases by infectious agents, leads to severe hyperinflammation. Familial forms of HLH (FHL), which are increasingly found also in adolescents and adults, are due to genetic defects leading to impaired function of natural killer cells and cytotoxic T cells. These mutations occur either in the perforin gene or in genes important for the exocytosis of cytotoxic granules. Cytotoxic granules contain perforin and granzymes, which induce apoptosis upon entering (infected) target cells. Additionally, perforin is important for the downregulation of the immune response. Acquired forms of HLH are encountered in association with (usually) viral infections, autoinflammatory/autoimmune diseases, malignant diseases, and acquired immune deficiency states (e.g., after organ transplantation). Treatment of HLH includes immune-suppressive and immune-modulatory agents, cytostatic drugs, and biological response modifiers. For patients with FHL, stem cell transplantation is indicated and can be curative.

Making sense of the cytokine storm: a conceptual framework for understanding, diagnosing, and treating hemophagocytic syndromes

Cytokine storm syndromes (CSS) are a group of disorders representing a variety of inflammatory causes. The clinical presentations of all CSS can be strikingly similar, creating diagnostic uncertainty. However, clinicians should avoid the temptation to treat all CSS equally, because their inciting inflammatory insults vary widely. Failure to identify and address this underlying trigger results in delayed, inoptimal, or potentially harmful consequences. This review places the hemophagocytic syndromes hemophagocytic lymphohistiocytosis and macrophage activation syndrome within a conceptual model of CSS and provides a logical framework for diagnosis and treatment of CSS of suspected rheumatic origin.

Hemophagocytic lymphohistiocytosis in adults: diagnosis and treatment

Hemophagocytic lymphohistiocytosis occurring as a primary or acquired disorder is a condition of chaotic and uncontrolled immune system stimulation. Cytotoxic cells and macrophages cause multiorgan damage, hemophagocytosis, and severe systemic inflammation. Clinical manifestations include a fever, organ enlargement, and weight loss. Laboratory tests show bicytopenia or pancytopenia, cytolysis and cholestasis, serum ferritin elevation, and clotting disorders. The reference standard for the diagnosis remains the presence in histological specimens of hemophagocytic macrophages, which may be lacking early in the disease, leading to diagnostic challenges. Inherited forms produce symptoms in early childhood and are fatal in the absence of specific treatment. In adults, the clinical spectrum ranges from mild and self-limited hemophagocytic lymphohistiocytosis to rapidly fatal multiorgan failure. Many questions remain unresolved regarding the diagnosis and treatment in adults. This update is an attempt at providing answers.

Not all hemophagocytes are created equally: appreciating the heterogeneity of the hemophagocytic syndromes

PURPOSE OF REVIEW

The deadly macrophage activation syndrome (MAS) constitutes one of the few rheumatologic emergencies. MAS is part of a larger group of diseases referred to as hemophagocytic syndromes that are seen in infections, malignancies, or genetic immunodeficiencies. Because of the clinical similarity of these diseases, many clinicians are tempted to approach them all similarly, both in diagnostic criteria and treatment paradigms. New work in the field suggests that not all hemophagocytic syndromes are equal. We will review the latest literature from both human and murine models related to the diagnosis, etiology, and treatment of hemophagocytic syndromes including MAS.

RECENT FINDINGS

More specific diagnostic criteria for the different hemophagocytic syndromes are being developed. Animal models suggest at least two different mechanisms by which hemophagocytic syndromes arise: enhanced antigen presentation and excessive Toll-like receptor signaling. Work in humans suggests different cytokine profiles, and different treatment strategies for the variety of hemophagocytic syndromes.

SUMMARY

The recent studies reviewed in this article suggest that despite clinical similarities the different hemophagocytic syndromes are indeed likely heterogeneous. Diagnostic criteria and treatment strategies tailored to the underlying disease or genetic context are needed and will hopefully be addressed by future work in this field.

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.

Alternative activation in systemic juvenile idiopathic arthritis monocytes

Systemic juvenile idiopathic arthritis (SJIA) is a chronic autoinflammatory condition. The association with macrophage activation syndrome, and the therapeutic efficacy of inhibiting monocyte-derived cytokines, has implicated these cells in SJIA pathogenesis. To characterize the activation state (classical/M1 vs. alternative/M2) of SJIA monocytes, we immunophenotyped monocytes using several approaches. Monocyte transcripts were analyzed by microarray and quantitative PCR. Surface proteins were measured at the single cell level using flow cytometry. Cytokine production was evaluated by intracellular staining and ELISA. CD14(++)CD16(-) and CD14(+)CD16(+) monocyte subsets are activated in SJIA. A mixed M1/M2 activation phenotype is apparent at the single cell level, especially during flare. Consistent with an M2 phenotype, SJIA monocytes produce IL-1β after LPS exposure, but do not secrete it. Despite the inflammatory nature of active SJIA, circulating monocytes demonstrate significant anti-inflammatory features. The persistence of some of these phenotypes during clinically inactive disease argues that this state reflects compensated inflammation.

Systemic arthritis in children: a review of clinical presentation and treatment

Systemic juvenile idiopathic arthritis (sJIA) constitutes a small part of juvenile idiopathic arthritis (JIA), yet has a disproportionally higher rate of mortality. Despite being grouped under JIA, it is considered to be a multifactorial autoinflammatory disease. The objective of this paper is to review the epidemiology, pathogenesis, genetics, clinical manifestations, complications, therapy, prognosis, and outcome of sJIA. The presentation and clinical manifestations of sJIA have not changed much in the past several decades, but the collective understanding of the pathogenesis and the development of new targeted therapies (particularly the biologic agents) have transformed and improved the disease outcome for children with sJIA.

Juvenile idiopathic arthritis

Juvenile idiopathic arthritis is a heterogeneous group of diseases characterised by arthritis of unknown origin with onset before age of 16 years. Pivotal studies in the past 5 years have led to substantial progress in various areas, ranging from disease classification to new treatments. Gene expression profiling studies have identified different immune mechanisms in distinct subtypes of the disease, and can help to redefine disease classification criteria. Moreover, immunological studies have shown that systemic juvenile idiopathic arthritis is an acquired autoinflammatory disease, and have led to successful studies of both interleukin-1 and interleukin-6 blockade. In other forms of the disease, synovial inflammation is the consequence of a disturbed balance between proinflammatory effector cells (such as T-helper-17 cells), and anti-inflammatory regulatory cells (such as FOXP3-positive regulatory T cells). Moreover, specific soluble biomarkers (S100 proteins) can guide individual treatment. Altogether these new developments in genetics, immunology, and imaging are instrumental to better define, classify, and treat patients with juvenile idiopathic arthritis.

Pathogenesis of systemic juvenile idiopathic arthritis: some answers, more questions

Systemic juvenile idiopathic arthritis (sJIA) has long been recognized as unique among childhood arthritides, because of its distinctive clinical and epidemiological features, including an association with macrophage activation syndrome. Here, we summarize research into sJIA pathogenesis. The triggers of disease are unknown, although infections are suspects. Once initiated, sJIA seems to be driven by innate proinflammatory cytokines. Endogenous Toll-like receptor ligands, including S100 proteins, probably synergize with cytokines to perpetuate inflammation. These and other findings support the hypothesis that sJIA is an autoinflammatory condition. Indeed, IL-1 is implicated as a pivotal cytokine, but the source of excess IL-1 activity remains obscure and the role of IL-1 in chronic arthritis is less clear. Another hypothesis is that a form of hemophagocytic lymphohistiocytosis underlies sJIA, with varying degrees of its expression across the spectrum of disease. Alternatively, sJIA with MAS might be a genetically distinct subtype. Yet another hypothesis proposes that inadequate downregulation of immune activation is central to sJIA, supporting evidence for which includes 'alternative activation' of monocyte and macrophages and possible deficiencies in IL-10 and T regulatory cells. Some altered immune phenotypes persist during clinically inactive disease, which suggests that this stage might represent compensated inflammation. Despite much progress being made, many questions remain, providing fertile ground for future research.

Critical care of the pediatric patient with rheumatic disease

PURPOSE OF REVIEW

Extensive systemic illness and treatment with immunosuppressive agents often require patients with rheumatic diseases to be monitored or managed in the pediatric intensive care unit. Additionally, severe disease-specific manifestations of childhood rheumatic disorders present pediatric rheumatologists and critical care physicians with diagnostic and treatment challenges. Although mortality from rheumatic disease in children is rare, the most severe diseases, such as pediatric systemic lupus erythematosus and juvenile dermatomyositis, remain life-threatening.

RECENT FINDINGS

Advances in therapy have reduced the incidence of severe complications of autoimmune and inflammatory diseases and have expanded treatment options. However, patients with active underlying rheumatic disease and secondary infection who are being treated with immunosuppressive agents are most at risk for poor outcomes.

SUMMARY

Here we discuss the complications of childhood rheumatic conditions that necessitate critical intervention. We discuss how improved understanding of the cellular and molecular basis of disease pathogenesis holds the promise of more targeted therapy without the adverse effects of global immunosuppression.

Gene expression profiling of peripheral blood mononuclear cells from children with active hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare, genetically heterogeneous autosomal recessive immune disorder that results when the critical regulatory pathways that mediate immune defense mechanisms and the natural termination of immune/inflammatory responses are disrupted or overwhelmed. To advance the understanding of FHL, we performed gene expression profiling of peripheral blood mononuclear cells from 11 children with untreated FHL. Total RNA was isolated and gene expression levels were determined using microarray analysis. Comparisons between patients with FHL and normal pediatric controls (n = 30) identified 915 down-regulated and 550 up-regulated genes with more than or equal to 2.5-fold difference in expression (P ≤ .05). The expression of genes associated with natural killer cell functions, innate and adaptive immune responses, proapoptotic proteins, and B- and T-cell differentiation were down-regulated in patients with FHL. Genes associated with the canonical pathways of interleukin-6 (IL-6), IL-10 IL-1, IL-8, TREM1, LXR/RXR activation, and PPAR signaling and genes encoding of antiapoptotic proteins were overexpressed in patients with FHL. This first study of genome-wide expression profiling in children with FHL demonstrates the complexity of gene expression patterns, which underlie the immunobiology of FHL.

Association of IRF5 polymorphisms with susceptibility to macrophage activation syndrome in patients with juvenile idiopathic arthritis

OBJECTIVE

Systemic-onset juvenile idiopathic arthritis (systemic JIA) and macrophage activation syndrome (MAS), the most devastating complication of systemic JIA, are characterized by abnormal levels of proinflammatory cytokines. Interferon regulatory factor 5 (IRF5) is a member of the IRF family of transcription factors, and acts as a master transcription factor in the activation of genes encoding proinflammatory cytokines. Polymorphisms in the IRF5 gene have been associated with susceptibility to autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis. Our aim was to assess associations of IRF5 gene polymorphisms with susceptibility to systemic JIA and MAS.

METHODS

Three IRF5 single-nucleotide polymorphisms (rs729302, rs2004640, and rs2280714) were genotyped using TaqMan assays in 81 patients with systemic JIA (33 with MAS, 48 without) and 190 controls.

RESULTS

There were no associations of the IRF5 gene polymorphisms or haplotypes under study with susceptibility to systemic JIA. There was a significant association of the rs2004640 T allele with MAS susceptibility (OR 4.11; 95% CI 1.84, 9.16; p = 0.001). The IRF5 haplotype (rs729302 A, rs2004640 T, and rs2280714 T), which was reported as conferring an increased risk of SLE, was significantly associated with MAS susceptibility in patients with systemic JIA (OR 4.61; 95% CI 1.73, 12.3; p < 0.001).

CONCLUSION

IRF5 gene polymorphism is a genetic factor influencing susceptibility to MAS in patients with systemic JIA, and IRF5 contributes to the pathogenesis of MAS in these patients.

Contemporary diagnostic methods for hemophagocytic lymphohistiocytic disorders

Hemophagocytic lymphohistiocytosis is a life-threatening multi-system hyperinflammatory disorder characterized by dysfunctional cytolytic lymphocyte responses, hypercytokinemia, and widespread lymphohistiocytic tissue infiltration and destruction. Diagnosis and definitive therapy are often delayed as clinical efforts are directed toward treatment of presumed overwhelming infection. Sporadic cases occur in association with underlying immune dysfunction related to autoimmune disease, malignancy, or severe infection. However, familial cases predominate with remarkable associations between underlying genetic defects and dysregulation of immune responses. Here, we review the genetic and immunologic basis of contemporary diagnostic methods for hemophagocytic lymphohistiocytosis.

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.

STX11 mutations and clinical phenotypes of familial hemophagocytic lymphohistiocytosis in North America

BACKGROUND

Mutations in STX11 are responsible for Familial Hemophagocytic Lymphohistiocytosis (FHLH) type 4, a rare primary immunodeficiency which has previously been observed only in patients of Kurdish, Turkish, and Lebanese ethnic background.

METHODS

We reviewed our experience with STX11 mutations among North American patients and studied the impact of patient mutations upon syntaxin 11 expression and NK cell function.

RESULTS

Between 2007 and 2008, 243 patients with HLH (lacking disease-causing mutations in PRF1 and UNC13D) were referred for STX11 mutational analysis. We observed 1 novel homozygous nonsense mutation, 73 G > T (E25X), occurring in Hispanic siblings, and 2 novel biallelic heterozygous missense mutations, 106G > C (E36Q) and 616G > A (E206K), occurring in 1 Caucasian patient. The N-terminal nonsense mutation resulted in absence of detectable syntaxin 11 and abrogation of in vitro NK cell degranulation and function, while the biallelic heterozygous missense mutations resulted in detectable mutated syntaxin 11 and preservation of in vitro NK cell degranulation and cytotoxicity. The two sibling patients with the nonsense mutations presented with HLH during infancy, whereas the patient with biallelic heterozygous missense mutations presented at 5 years of age.

CONCLUSION

We conclude that mutations in STX11 are responsible for HLH in approximately 1% of North American patients and can cause variable defects in syntaxin 11 expression and function with resultant impact on clinical phenotype.

Cytomegalovirus infection in pediatric rheumatic diseases: a review

Human cytomegalovirus (HCMV) is familiar to pediatric rheumatologists mainly as a cause of opportunistic disease in pharmacologically immune suppressed patients. However, HCMV also has a variety of immuno-modulatory effects, through which it may influence the course of rheumatic conditions. In this article we discuss the interplay between HCMV and the immune system, and review the clinical manifestations, diagnosis, and treatment of HCMV infection in children with rheumatic disease.

An overview of genetics of paediatric rheumatic diseases

The evidence so far suggests that the paediatric inflammatory diseases encountered in rheumatology practice may be largely genetic in origin, where common single nucleotide polymorphisms (SNPs) in multiple genes contribute to risk, with real but variable environmental components. As far as genetic susceptibility to common paediatric rheumatic diseases is concerned, only juvenile idiopathic arthritis (JIA) has been investigated in any substantial way so far. This article discusses susceptibility for different types of JIA, the different methods used and their advantages and disadvantages. The genetic code is also modifiable by epigenetic mechanisms and examples of these in immunity and rheumatoid arthritis are given to indicate another area of research in the elucidation of the genetics of paediatric rheumatic diseases.

D-penicillamine-induced autoimmunity: relationship to macrophage activation

Idiosyncratic drug reactions represent a serious health problem, and they remain unpredictable largely due to our limited understanding of the mechanisms involved. Penicillamine-induced autoimmunity in Brown Norway (BN) rats represents one model of an idiosyncratic reaction, and this drug can also cause autoimmune reactions in humans. We previously demonstrated that penicillamine binds to aldehydes on the surface of macrophages. There is evidence that an imine bond formed by aldehyde groups on macrophages and amine groups on T cells is one type of interaction between these two cells that is involved in the induction of an immune response. We proposed that the binding of penicillamine with aldehyde groups on macrophages could lead to their activation and in some patients could lead to autoimmunity. In this study, the transcriptome profile of spleen macrophages 6 h after penicillamine treatment was used to detect effects of penicillamine on macrophages with a focus on 20 genes known to be macrophage activation biomarkers. One biological consequence of macrophage activation was investigated by determining mRNA levels for IL-15 and IL-1 beta which are crucial for NK cell activation, as well as levels of mRNA for selected cytokines in spleen NK cells. Up-regulation of the macrophage activating cytokines, IFN-gamma and GM-CSF, and down-regulation of IL-13 indicated activation of NK cells, which suggests a positive feedback loop between macrophages and NK cells. Furthermore, treatment of a murine macrophage cell line, RAW264.7, with penicillamine increased the production of TNF-alpha, IL-6, and IL-23, providing additional evidence that penicillamine activates macrophages. Hydralazine and isoniazid cause a lupus-like syndrome in humans and also bind to aldehyde groups. These drugs were also found to activate RAW264.7 macrophages. Together, these data support the hypothesis that drugs that bind irreversibly with aldehydes lead to macrophage activation, which in some patients can lead to an autoimmune syndrome.

Mutations in the perforin gene can be linked to macrophage activation syndrome in patients with systemic onset juvenile idiopathic arthritis

OBJECTIVE

Macrophage activation syndrome (MAS) in systemic onset juvenile idiopathic arthritis (SoJIA) is considered to be an acquired form of familial haemophagocytic lymphohistiocytosis (fHLH). FHLH is an autosomal recessive disorder, characterized by diminished NK cell function and caused by mutations in the perforin gene (PRF1) in 20-50% of patients. Interestingly, SoJIA patients display decreased levels of perforin in NK cells and diminished NK cell function as well. Here, we analysed PRF1 and its putative promoter in SoJIA patients with or without a history of MAS.

METHODS

DNA of 56 SoJIA patients (41 Italian and 15 Dutch) was isolated. Of these, 15 (27%) had a confirmed history of MAS. We sequenced PRF1 and 1.5 kb of the 5'-upstream region. DNA sequence variations in the promoter region were functionally tested in transfection experiments using a human NK cell line.

RESULTS

We detected a previously undescribed sequence variation (-499 C > T) in the promoter of PRF1 in 18% of the SoJIA patients. However, transfection experiments did not show functional implications of this variation. Secondly, we found that 11 of 56 (20%) SoJIA patients were heterozygous for missense mutations in PRF1. In particular, we found a high prevalence of the Ala91Val mutation, a variant known to result in defective function of perforin. Interestingly, the prevalence of Ala91Val in SoJIA patients with a history of MAS (20%) was increased compared with SoJIA patients without MAS (9.8%). One SoJIA patient, heterozygous for Ala91Val, showed profound decreased perforin levels at the time of MAS.

CONCLUSIONS

These findings suggest that PRF1 mutations play a role in the development of MAS in SoJIA patients.

Histiocytic disorders: recent insights into pathophysiology and practical guidelines

The Histiocytoses are defined as non-malignant disorders due to abnormal accumulation and behavior of cells of the mononuclear phagocytic system. The best known histiocytoses, Langerhans cell histiocytosis (LCH), and hemophagocytic lymphohistiocytosis (HLH), each with an estimated incidence of 1/50,000 to 1/150,000, are sufficiently "common," complex and costly, to constitute an important problem in medical practice. At the same time, LCH, HLH and an array of other and more rare histiocytoses are sufficiently uncommon that most physicians lack the experience to diagnose, let alone care for patients with these conditions. The pathophysiology of most of the histiocytoses is unknown and, in the case of the widely-disseminated and potentially fatal forms, treatments to date have been variably effective and sometimes highly toxic. MAS has been reported to occur in association with almost any rheumatic disease, it is by far most common in the systemic form of Juvenile Idiopthic Arthritis (SoJIA). It is now recognized that MAS bears a close resemblance to Hemophagocytic Lymphohistiocytosis or HLH, and MAS is recognized as the major fatal complication of soJIA.

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.

Horror autoinflammaticus: the molecular pathophysiology of autoinflammatory disease (*)

The autoinflammatory diseases are characterized by seemingly unprovoked episodes of inflammation, without high-titer autoantibodies or antigen-specific T cells. The concept was proposed ten years ago with the identification of the genes underlying hereditary periodic fever syndromes. This nosology has taken root because of the dramatic advances in our knowledge of the genetic basis of both mendelian and complex autoinflammatory diseases, and with the recognition that these illnesses derive from genetic variants of the innate immune system. Herein we propose an updated classification scheme based on the molecular insights garnered over the past decade, supplanting a clinical classification that has served well but is opaque to the genetic, immunologic, and therapeutic interrelationships now before us. We define six categories of autoinflammatory disease: IL-1beta activation disorders (inflammasomopathies), NF-kappaB activation syndromes, protein misfolding disorders, complement regulatory diseases, disturbances in cytokine signaling, and macrophage activation syndromes. A system based on molecular pathophysiology will bring greater clarity to our discourse while catalyzing new hypotheses both at the bench and at the bedside.

A comprehensive review of the genetics of juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common chronic arthropathy of childhood which is believed to be influenced by both genetic and environmental factors. The progress in identifying genes underlying JIA susceptibility using candidate gene association studies has been slow. Several associations between JIA and variants in the genes encoding the human leukocyte antigens (HLA) have been confirmed and replicated in independent cohorts. However it is clear that genetic variants outside the HLA also influence susceptibility to JIA. While a large number of non-HLA candidate genes have been tested for associations, only a handful of reported associations such as PTPN22 have been validated. In this review we discuss the principles behind genetic studies of complex traits like JIA, and comprehensively catalogue non-HLA candidate-gene association studies performed in JIA to date and review several validated associations. Most candidate gene studies are underpowered and do not detect associations, and those that do are often not replicated. We also discuss the principles behind genome-wide association studies and discuss possible implications for identifying genes underlying JIA. Finally we discuss several genetic variants underlying multiple clinically distinct autoimmune phenotypes.