Acid labile alpha-interferon in sera and synovial fluids from patients with juvenile arthritis

Association between type I interferon pathway activation and clinical outcomes in rheumatic and musculoskeletal diseases: a systematic literature review informing EULAR points to consider

BACKGROUND

Type I interferons (IFN-I) contribute to a broad range of rheumatic and musculoskeletal diseases (RMDs). Compelling evidence suggests that the measurement of IFN-I pathway activation may have clinical value. Although several IFN-I pathway assays have been proposed, the exact clinical applications are unclear. We summarise the evidence on the potential clinical utility of assays measuring IFN-I pathway activation.

METHODS

A systematic literature review was conducted across three databases to evaluate the use of IFN-I assays in diagnosis and monitor disease activity, prognosis, response to treatment and responsiveness to change in several RMDs.

RESULTS

Of 366 screened, 276 studies were selected that reported the use of assays reflecting IFN-I pathway activation for disease diagnosis (n=188), assessment of disease activity (n=122), prognosis (n=20), response to treatment (n=23) and assay responsiveness (n=59). Immunoassays, quantitative PCR (qPCR) and microarrays were reported most frequently, while systemic lupus erythematosus (SLE), rheumatoid arthritis, myositis, systemic sclerosis and primary Sjögren's syndrome were the most studied RMDs. The literature demonstrated significant heterogeneity in techniques, analytical conditions, risk of bias and application in diseases. Inadequate study designs and technical heterogeneity were the main limitations. IFN-I pathway activation was associated with disease activity and flare occurrence in SLE, but their incremental value was uncertain. IFN-I pathway activation may predict response to IFN-I targeting therapies and may predict response to different treatments.

CONCLUSIONS

Evidence indicates potential clinical value of assays measuring IFN-I pathway activation in several RMDs, but assay harmonisation and clinical validation are urged. This review informs the EULAR points to consider for the measurement and reporting of IFN-I pathway assays.

Emerging concepts of type I interferons in SLE pathogenesis and therapy

Type I interferons have been suspected for decades to have a crucial role in the pathogenesis of systemic lupus erythematosus (SLE). Evidence has now overturned several long-held assumptions about how type I interferons are regulated and cause pathological conditions, providing a new view of SLE pathogenesis that resolves longstanding clinical dilemmas. This evidence includes data on interferons in relation to genetic predisposition and epigenetic regulation. Importantly, data are now available on the role of interferons in the early phases of the disease and the importance of non-haematopoietic cellular sources of type I interferons, such as keratinocytes, renal tubular cells, glial cells and synovial stromal cells, as well as local responses to type I interferons within these tissues. These local effects are found not only in inflamed target organs in established SLE, but also in histologically normal skin during asymptomatic preclinical phases, suggesting a role in disease initiation. In terms of clinical application, evidence relating to biomarkers to characterize the type I interferon system is complex, and, notably, interferon-blocking therapies are now licensed for the treatment of SLE. Collectively, the available data enable us to propose a model of disease pathogenesis that invokes the unique value of interferon-targeted therapies. Accordingly, future approaches in SLE involving disease reclassification and preventative strategies in preclinical phases should be investigated.

Nitric oxide synthase 2 and cyclooxygenase 2 interactions in inflammation

Nitric oxide (NO) and prostaglandin (PG) E2 produced by NO synthase type 2 (NOS2) and cyclooxygenase type 2 (COX2), respectively, are important mediators in inflammation. There is much information regarding their roles in models of inflammation in mice and in humans with diseases such as rheumatoid arthritis (RA). A variety of stimuli including cytokines, microbial components, immune complexes, and mechanical stress can induce both NOS2 and COX2 mRNA transcription and protein synthesis and enhance inflammation. This has been demonstrated in both mice and humans. NOS2-specific inhibitors reduce inflammation in mice, and COX2-specific inhibitors reduce inflammation in mice and in humans. There is significant cross-talk between PGE2/NO and COX2/NOS2. Treatments that inhibit both NOS2 and COX2 should provide the most potent antiinflammatory effects.

Cytokine gene polymorphisms and susceptibility to juvenile idiopathic arthritis. British Paediatric Rheumatology Study Group

OBJECTIVE

To investigate the involvement of candidate cytokine genes in the pathogenesis of juvenile idiopathic arthritis (JIA).

METHODS

Single nucleotide polymorphisms and intragenic microsatellite markers within 8 candidate cytokine genes (interleukin-1alpha [IL-1alpha], IL-2, IL-4, IL-6, IL-10, interferon-alpha1 [IFNA1], interferon-gamma [IFNG], and interferon regulatory factor 1 [IRF-1]) were investigated in 417 Caucasian patients with clinically characterized JIA and a panel of 276 unrelated, healthy Caucasian controls, all from the United Kingdom.

RESULTS

A novel 3'-untranslated region (3'UTR) polymorphism in IRF-1 was found to be associated with susceptibility to JIA (corrected P = 0.002). No significant association with IL-1alpha, IL-2, IL-4, IL-6, IL-10, IFNA1, or IFNG was observed.

CONCLUSION

An association between JIA and a previously unreported 3'UTR polymorphism of IRF-1 was observed. This association was not found to be specific to any particular JIA subgroup. This suggests that IRF-1 may contribute to a common pathogenesis shared by all JIA patients, regardless of clinical phenotype. This is most likely to be a genetic contribution to the chronic inflammatory process that underlies JIA pathology.

Anti-cytokine autoantibodies: epiphenomenon or critical modulators of cytokine action

Low amounts of high-affinity autoantibodies to various cytokines have been detected in sera from healthy donors. Their levels, although highly variable, are increased in the circulation of patients subjected to cytokine therapy or suffering from a variety of immunoinflammatory diseases. It has been suggested that these autoantibodies play a regulatory role in the intensity and duration of an immune response. The antibodies may prevent the binding of a cytokine to its specific cell surface receptor thereby neutralizing its biological activity in vivo. They may also act as carrier proteins preventing the rapid elimination of a cytokine from the circulation and thus increase its bioactivity. Additionally or alternatively, autoantibodies may modulate cytokine-induced intracellular signal transduction pathways or trigger complement-mediated cytotoxicity towards cells carrying membrane-bound cytokines. The autoantibodies may exert their regulatory role in compliance with the other factors that control cytokine activity, including soluble cytokine receptors, cell surface decoy receptors, and receptor antagonists. Although not favored by many investigators, a less sophisticated role for naturally occurring anti-cytokine autoantibodies should be considered as well. Recent evidence has shown that autoantibodies are generated at a high frequency as part of a response to foreign antigens. These antibodies are produced by B cells arising from the process of somatic mutation. Thus anti-cytokine autoantibodies may be the result of a "leaky" B cell response triggered by immunoinflammatory processes. High-titered autoantibodies induced by cytokine therapy are of clinical concern since their occurrence is often associated with the loss of response to treatment. Moreover, they may also neutralize endogenously produced cytokines with possible pathological consequences. In this paper we have reviewed the available information on the biological and clinical significance of both naturally occurring and therapeutically induced anti-cytokine autoantibodies in animals and man with the emphasis on antibodies directed to interferons.

Human natural interferon-alpha producing cells

Interferons (IFNs) are critical components of the host immune system, serving as antiviral agents, immunomodulators and inhibitors of cell growth. Among peripheral blood mononuclear cells, the primary IFN-alpha-producing cell is a light density, HLA-DR+ cell negative for cell surface markers typical for T cells, B cells, monocytes, natural-killer or progenitor cells and has been tentatively termed the 'natural IFN-producing cell' or NIPC. Although present in very low frequency (approximately 1:1000 among peripheral blood mononuclear cells), the NIPC are very potent, with an individual cell able to produce 1-2 IU of IFN. In this review, the characteristics, phenotype, regulation and relationship of NIPC to human disease are discussed.

Serum activity that confers acid lability to alpha-interferon in systemic lupus erythematosus: its association with disease activity and its independence from circulating alpha-interferon

We conducted a longitudinal evaluation of a patient with systemic lupus erythematosus who constitutively exhibited elevated levels of circulating alpha-interferon (alpha-IFN). This study demonstrated that the serum levels of an activity that renders the endogenous alpha-IFN acid labile are positively correlated with disease activity. This IFN acid lability-inducing activity can also be found in the sera of systemic lupus erythematosus patients who have active disease but who do not have circulating alpha-IFN.

Interferon alpha associated with systemic lupus erythematosus is not intrinsically acid labile

The physicochemical properties of apparently acid-labile IFN-alpha from patients with SLE have been studied. The antigenicity, apparent molecular size, and isoelectric point of SLE IFN-alpha are indistinguishable from those of conventional, previously characterized, acid-stable subspecies of IFN-alpha. However, after partial purification by anion-exchange chromatography, SLE IFN-alpha no longer exhibits acid lability, suggesting that other plasma factor(s) are responsible for the acid lability of SLE IFN-alpha. Addition of SLE plasma, but not normal plasma, to conventional acid-stable IFN-alpha renders the exogenous IFN-alpha acid labile. Preliminary results demonstrate that an acid-dependent IFN-inactivating activity can be partially purified from SLE plasma by anion-exchange chromatography.

AIDS and autoimmunity

While much evidence appears to support the hypothesis of AIDS being an autoimmune disease, equally impressive facts negate the theory. At most, one can presently speak only of the "autoimmune features" of this very complex syndrome. AIDS most strikingly presents with various autoantibodies including those directed against both red and white blood cells. These antibodies appear to be - at least in part - responsible for some of the autoimmune features of the disease. Several clinical and serological similarities exist between AIDS and the "classic" autoimmune disease SLE. In fact, following the isolation of HIV, researchers once again began searching for a viral etiology of SLE. It appears that while autoimmune mechanisms may explain some of the clinical and serologic manifestations of the disease, not enough evidence exists as yet to decidedly point either for or against its classification as an autoimmune disease.

Interferons and autoimmunity

Autoimmunity can be accelerated in several genetically prone murine models and can even be induced in normal mice by treatment with interferon (IFN) or IFN-inducers. Several cases of IFN-induced autoimmune disease in humans also have been observed; however, more striking is the fact that some of the clinical manifestations in autoimmune diseases and many of the immunological aberrations can be mediated or enhanced by IFN. The finding of high levels of circulating IFN in many patients may be highly significant in that respect, and the characterization of the predominant type of IFN as an unusual acid-labile IFN-alpha may indicate an infectious etiologic agent in autoimmunity, since this peculiar IFN was mostly associated with viral infections in vivo or in vitro. The induction of MHC class II antigens on previously HLA-DR or Ia negative cells appears to be caused primarily by IFN-gamma and may have a central role in the pathogenesis of autoimmunity in susceptible individuals. Such aberrant HLA-DR expression on nonlymphoid cells can be detected early in the disease in the target organs of many varied autoimmune conditions and may trigger a cascade of self-directed, uncontrolled immune response in conjunction with other factors.

Peripheral blood and synovial fluid monocyte activation in inflammatory arthritis. II. Low levels of synovial fluid and synovial tissue interferon suggest that gamma-interferon is not the primary macrophage activating factor

Because synovial fluid monocytes (SFM) in patients with inflammatory arthritis bear an activated phenotype (i.e., high expression of HLA-DR and low expression of the monocyte differentiation antigen Mo2), we assessed the role of gamma-interferon (gamma-IFN) in the activation of these cells. Sensitive and specific radioimmunoassays detected only 0.40 +/- 0.20 units/ml of gamma-IFN in the SF of patients with rheumatoid arthritis (RA) and 0.61 +/- 0.67 units/ml of gamma-IFN in the SF of patients with other forms of chronic inflammatory arthritis. There was no detectable alpha-IFN in any SF studied by radioimmunoassay. Bioassays failed to detect nonimmunoreactive IFN. Synovial tissue (ST) explants produced very little gamma-IFN (0.14 +/- 0.091 units/ml), and production was not increased by the presence of indomethacin in the cultures or by removal of adherent cells. However, gamma-IFN was produced if ST was cultivated in the presence of phytohemagglutinin. In SF and ST supernatants, gamma-IFN-mediated induction of HLA-DR on monocytes was inhibited, even though the amount of immunoreactive IFN was not affected. Prostaglandin E2 was shown to be one possible inhibitor. We demonstrated that a factor that induces HLA-DR on some individuals' peripheral blood monocytes, and cannot be neutralized by monoclonal anti-gamma-IFN antibody, is present in SF and ST supernatants. These data suggest that activation of SFM may occur by mechanisms other than gamma-IFN.

Immunological abnormalities in juvenile chronic arthritis

The immunological alterations that have been reported in juvenile chronic arthritis are reviewed. Their role in patient management and classification as well as their possible etiopathogenetic relevance are discussed.

Effects of interferon-alpha on the expression of a lupus idiotype in normal humans

Interferon (IFN) has extensive immunoregulatory effects but its role in systemic lupus erythematosus (SLE) remains obscure. The observations that a high proportion of patients with active SLE have increased IFN levels in their sera, and that IFN injected to lupus-prone mice aggrevates their disease, led us to examine the effects of IFN on the production of 16/6--a high frequency idiotype of monoclonal anti-DNA antibodies produced by human-human hybridomas derived from SLE patients. Peripheral blood mononuclear cells (PBMC) of healthy donors or of patients with SLE were incubated with IFN and pokeweed mitogen (PWM). Seven-day supernatants were assayed for total IgM, for IgM with 16/6 idiotype, and for IgM anti-DNA activity. PWM-stimulated PBMC of all healthy donors examined produced the 16/6 idiotype (mean 2.5 ng/ml). A significant increase of 16/6 in normals (above the level with PWM alone) was noted with 10-100 u/ml of IFN-alpha but not with 500 u/ml. In 3/10 normals the addition of IFN-alpha resulted in detectable anti-DNA activity. The IFN-induced increase in 16/6 idiotype was significantly more than the increase in IgM (335% vs 47% above baseline, with 10 u/ml of IFN). These effects of IFN could not be demonstrated in the absence of PWM nor in T-cell-depleted preparations. Recombinant IFN-gamma had no augmenting effect on 16/6 production. Three SLE patients in remission had elevated levels of 16/6 in their PBMC supernatant (15-200 ng/ml) which could not be further augmented by IFN. Thus, we have demonstrated the potential of PWM-stimulated normal lymphocytes to generate a "lupus" idiotype and shown that production of this idiotype requires T cells and is preferentially enhanced by IFN-alpha. Further studies of the effects of IFN on the expression of anti-DNA antibodies may clarify a postulated role of IFN in autoimmune diseases.

Monoclonal antibodies against complement 3 neoantigens for detection of immune complexes and complement activation. Relationship between immune complex levels, state of C3, and numbers of receptors for C3b

C3-bearing immune complexes and C3 activation products were detected by using two monoclonal antibodies, one specific for a neoantigenic determinant on C3c and the other for C3d. To quantitate immune complexes, the anti-C3c or anti-C3d antibodies were fixed to microtiter plates and reacted with test plasma. The binding of C3-bearing immune complexes in this plasma was then measured with radioisotope- or enzyme-labeled anti-human IgG. To test for C3 breakdown products, solid-phase monoclonal antibody to the C3d neoantigen was reacted with EDTA-plasma samples, and fixed iC3b or C3d was measured with a polyclonal anti-C3 antibody. Patients with autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and Sjogren's syndrome, and paracoccidioidomycosis were found to contain immune complexes bearing C3b/iC3b or C3d. In most conditions, there were more C3d-containing immune complexes than C3b/iC3b. Although CR1 (C3b receptors) rapidly converted immune complex-bound iC3b to C3dg/C3d and lupus patients had reduced CR1, no correlation between the state of C3 on circulating immune complexes or levels of immune complexes and CR1 numbers was seen. However, levels of C3-fixing ICs correlated with levels of C3 activation products. This assay system with monoclonal antibodies to neoantigens expressed on activated, but not native, C3 provides sensitive and specific means for detecting and classifying C3-fixing immune complexes and for assessing C3 activation.