Circulating immune complexes in patients with progressive systemic sclerosis

Osteopontin Links Myeloid Activation and Disease Progression in Systemic Sclerosis

Progressive lung fibrosis is a major cause of mortality in systemic sclerosis (SSc) patients, but the underlying mechanisms remain unclear. We demonstrate that immune complexes (ICs) activate human monocytes to promote lung fibroblast migration partly via osteopontin (OPN) secretion, which is amplified by autocrine monocyte colony stimulating factor (MCSF) and interleukin-6 (IL-6) activity. Bulk and single-cell RNA sequencing demonstrate that elevated OPN expression in SSc lung tissue is enriched in macrophages, partially overlapping with CCL18 expression. Serum OPN is elevated in SSc patients with interstitial lung disease (ILD) and prognosticates future lung function deterioration in SSc cohorts. Serum OPN levels decrease following tocilizumab (monoclonal anti-IL-6 receptor) treatment, confirming the connection between IL-6 and OPN in SSc patients. Collectively, these data suggest a plausible link between autoantibodies and lung fibrosis progression, where circulating OPN serves as a systemic proxy for IC-driven profibrotic macrophage activity, highlighting its potential as a promising biomarker in SSc ILD.

Immune complexes induce osteopontin (OPN) secretion from macrophages via MCSF and IL-6

OPN is expressed predominantly by macrophages in fibrotic interstitial lung disease

Circulating OPN levels are elevated and predict disease progression in systemic sclerosis

IL-6 receptor blockade reduces levels of circulating OPN in systemic sclerosis patients

Immune complexes containing scleroderma-specific autoantibodies induce a profibrotic and proinflammatory phenotype in skin fibroblasts

Background

In systemic sclerosis (SSc), autoantibodies provide the most accurate tool to predict the disease subset and pattern of organ involvement. Scleroderma autoantibodies target nucleic acids or DNA/RNA-binding proteins, thus SSc immune complexes (ICs) can embed nucleic acids. Our working hypothesis envisaged that ICs containing scleroderma-specific autoantibodies might elicit proinflammatory and profibrotic effects in skin fibroblasts.

Methods

Fibroblasts were isolated from skin biopsies obtained from healthy subjects and patients with diffuse cutaneous SSc (dcSSc). ICs were purified by polyethylene-glycol precipitation from sera of SSc patients bearing different autoantibodies. ICs from patients with systemic lupus erythematosus (SLE) and primary anti-phospholipid syndrome (PAPS) and from normal healthy subjects (NHS) were used as controls. After incubation with ICs, fibroblasts were evaluated for ICAM-1 expression, interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1, matrix metalloproteinase (MMP)-2, tumor growth factor (TGF)-β1 and Pro-CollagenIα1 secretion, collagen (col)Iα1, mmp-1, toll-like receptor (tlr)2, tlr3, tlr4, tlr7, tlr8, tlr9, interferon (ifn)-α, ifn-β and endothelin-1 mRNA, and NFκB, p38MAPK and SAPK-JNK activation rate. Experiments were also performed after pretreatment with DNase I/RNase and NFκB/p38MAPK inhibitors.

Results

The antigenic reactivity for each SSc-IC mirrored the corresponding serum autoantibody specificity, while no positivity was observed in NHS-ICs or sera. SSc-ICs but not NHS-ICs increased ICAM-1 expression, stimulated IL-6, IL-8, MMP-2, MCP-1, TGF-β1 and Pro-CollagenIα1 secretion, upregulated et-1, ifn-α, ifn-β, tlr2, tlr3 and tlr4, and activated NFκB, p38MAPK and SAPK-JNK. tlr9 was significantly upregulated by ARA-ICs, mmp-1 was significantly induced by ACA-ICs whereas colIα1 was not modulated by any SSc-ICs. SLE-ICs and PAPS-ICs significantly upregulated MMP-2 and activated NFκB, p38MAPK and SAPK-JNK. SLE-ICs and PAPS-ICs did not affect colIα1, mmp-1 and Pro-CollagenIα1. DNase I and RNase treatment significantly reduced the upregulation of study mediators induced by SSc-ICs. Pretreatment with NFκB/p38MAPK inhibitors suggested that response to anti-Th/To-ICs was preferentially mediated by p38MAPK whereas ATA-ICs, ACA-ICs and ARA-ICs engaged both mediators. In dcSSc fibroblasts, stimulation with SSc-ICs and NHS-ICs upregulated IL-6 and IL-8.

Conclusions

These data provide the first demonstration of the proinflammatory and profibrotic effects of SSc-ICs on fibroblasts, suggesting the potential pathogenicity of SSc autoantibodies. These effects might be mediated by Toll-like receptors via the interaction with nucleic acid fragments embedded in SSc-ICs.

Complement activation in atypical hemolytic uremic syndrome and scleroderma renal crisis: a critical analysis of pathophysiology

Scleroderma is an autoimmune disease that affects multiple systems. While pathophysiologic mechanisms governing the development of scleroderma are relatively poorly understood, advances in our understanding of the complement system are clarifying the role of complement pathways in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis. The abundant similarities in their presentation as well as the clinical course are raising the possibility of a common underlying pathogenesis. Recent reports are emphasizing that complement pathways appear to be the unifying link. This article reviews the role of complement system in the development of atypical hemolytic uremic syndrome and scleroderma renal crisis, and calls for heightened awareness to the development of thrombotic angiopathy in patients with scleroderma.

Analysis of complement biomarkers in systemic sclerosis indicates a distinct pattern in scleroderma renal crisis

BACKGROUND

The complement system has been implicated in pathogenesis of systemic sclerosis (SSc). The goal of the present study was to evaluate improved complement biomarkers in SSc.

METHODS

The presence of C4d, reflecting activation of the classical/lectin pathways, C3bBbP corresponding to activation of the alternative pathway, and soluble terminal complement complexes (all complement pathways), was measured in plasma samples by enzyme-linked immunosorbent assay and correlated to clinical parameters. The study included 81 patients with limited cutaneous SSc and 41 with diffuse cutaneous SSc, as well as 47 matched healthy controls and 81 patients with rheumatoid arthritis, 22 with psoriatic arthritis and 20 with ankylosing spondylitis. Skin and kidney biopsies of selected patients were stained to detect deposited C3b as a marker of local complement activation.

RESULTS

Biomarkers of activation of all complement pathways were increased in SSc compared with healthy controls and were similar to those in other rheumatic diseases. When patients with SSc were divided into subgroups, a distinct pattern of complement markers was observed in individuals with scleroderma renal crisis (SRC). By functional assay, we confirmed a significant decrease in complement haemolytic activity in SRC vs. non-SRC patients, indicating complement consumption. Further, we detected glomerular deposits of C3b in some patients with SRC.

CONCLUSIONS

The data indicate that complement activation is an important feature of SRC.

The complement system and systemic sclerosis

Serum concentrations of the various complement components including the classical and the alternative pathways were determined in 58 control healthy subjects and 80 patients with systemic sclerosis (SSC). The mean concentrations of C1q, C2, C5, C6, C7, C9, and factor B were significantly increased in the SSC patients in comparison to controls, while the increases were not significant for C3 and C8. C4 was an exception in that the mean levels were found to be decreased, with 18 patients having levels < 65% of the mean normal value. Properdin was also found to be decreased, but not significantly. We found a similarity between the pattern of serum complement component concentrations in SSC patients and patients with primary biliary cirrhosis, two disorders frequently associated in the same patients. The significance of complement component patterns in these diseases is discussed.

Immunological abnormalities in a group of patients with limited cutaneous systemic sclerosis and prominent vascular disease

Antinuclear antibodies, circulating immune complexes, rheumatoid factors and anticardiolipin antibodies were detected in the sera of 17 patients affected by the limited cutaneous subset of systemic sclerosis and marked clinical evidence of ischaemic cutaneous lesions (fingertip ulcerations). This study was designed to evaluate the possible role of anticardiolipin (aCL) antibodies and other immunological disorders in the endothelial damage characteristic of the disease. ACL antibodies were found in 41% of the patients. With the exception of a significant connection with positive rheumatoid factor tests (RIA), no notable associations between anticardiolipin antibodies and antinuclear antibodies, circulating immune complexes (CIC), and other serological abnormalities were found. ACL antibodies did not significantly correlate with the presence of vascular lesions in our patients. However, a role of these antibodies in endothelial damage cannot be excluded, possibly in association with other serum factors such as immune complexes and antinuclear antibodies. A positive connection between the incidence of CIC and the severity of lung perfusion impairment was observed, and the previously reported relationship between anticentromere antibodies and calcinosis was indirectly confirmed.

Activation of the complement system in systemic sclerosis. Relationship to clinical severity

Using newly developed techniques, we investigated the complement pathways and the extent of their activation in patients with systemic sclerosis (SSc) of both the diffuse cutaneous and limited cutaneous types. Plasma levels of the fragments C3d, C4d, and Ba were measured in patients with SSc and in matched control subjects. All fragments and ratios were higher in SSc patients than in controls (P less than 0.05), demonstrating that complement activation occurs in SSc. Levels of C3d, C3d:C3, Ba, and Ba:factor B were higher in patients with diffuse cutaneous SSc patients than in controls (P less than 0.01). C3d, C3d:C3, C4d, and C4d:C4 levels were also higher in patients with limited cutaneous SSc than in controls (P less than 0.05). These results show that complement activation occurs in SSc patients and that it reflects clinical severity. Complement activation may therefore have a pathogenetic role in SSc, and its measurement may prove useful in monitoring the disease.

Progressive systemic sclerosis: mode of presentation, rapidly progressive disease course, and mortality based on an analysis of 91 patients

The overwhelming majority of patients with PSS present with combinations of Raynaud's phenomenon, sclerodactyly, polyarthralgias, or swelling of an extremity. However, the clinical presentation of PSS may be atypical; 14% of patients in the present series initially sought medical attention for symptoms other than Raynaud's phenomenon, tight skin, or joint pain. In the present series, only 31% of patients fulfilled the ARA criteria for PSS at the time of initial medical evaluation. Most patients manifested advanced disease by the time the criteria were fulfilled. The ARA criteria for the classification of PSS appear to have limited value with regard to making the diagnosis in an individual patient. Rapidly progressive PSS occurred in 17.6% of patients in this series and represents a particularly fulminant form of the disease whose course may not be predictable on clinical grounds at the time of initial medical evaluation or diagnosis. Patients destined to develop renal or cardiorespiratory failure usually do so in the first 3 years of disease. Close observation of PSS patients during the first 12 to 18 months may serve to identify those individuals who will undergo an accelerated disease course. Prognosis for patients with rapidly progressive PSS is poor and is associated with significantly higher mortality compared with patients with a more protracted disease course. Future therapeutic trials in PSS should be designed with the recognition that a subgroup of patients with this disorder will have a rapidly progressive disease course.

Plasma exchange in the treatment of nonadvanced stages of progressive systemic sclerosis

Ten patients suffering from progressive systemic sclerosis, who responded poorly to conventional therapy, underwent plasma exchange (PE) therapy in conjunction with drug therapy. The frequency of PE was twice weekly for 4-6 weeks, two or three times per year, with a summer interruption, when in our own experience a spontaneous relief of symptoms occurs. To judge the efficacy of our therapeutic device, we assessed several laboratory and clinical parameters before and after therapy. The changes in circulating immune complexes, in IgG and IgA, and in some functional indices were significant (P less than 0.001). Eight of 10 patients improved satisfactorily. The remaining two did not improve sufficiently to continue the apheretic treatment. In conclusion, our study suggests that the PE, together with conventional therapy, can be an effective therapeutic device in the treatment of progressive systemic sclerosis.

Interstitial lung disease in scleroderma. Immune complexes in sera and bronchoalveolar lavage fluid

Interstitial lung disease is a common feature of scleroderma (systemic sclerosis), and it may be a major determinant of morbidity and mortality. Analysis of bronchoalveolar lavage fluid from patients with scleroderma has shown evidence of inflammation in the lower respiratory tract of many patients. We have analyzed sera and bronchoalveolar lavage fluid from scleroderma patients for the presence of immune complexes, which may play a role in the inflammatory process. Using a solid-phase C1q enzyme-linked immunosorbent assay, we detected immune complexes in the sera of 6 of 23 patients (26%) and in none of 32 controls (P less than 0.01). All 6 patients with serum immune complexes had inflammatory cells in bronchoalveolar lavage fluid, and the presence of serum immune complexes correlated with the percentage of neutrophils in lavage fluid (P less than 0.02). Immune complexes were detected in lavage fluid of 11 of 21 patients (52%) compared with 1 of 7 normal controls (14%). Subjects having immune complexes in lavage fluid had a lower forced vital capacity than did those without lavage fluid immune complexes (P less than 0.05). The levels of immune complexes in bronchoalveolar lavage fluid exceeded those in serum by a mean of 45-fold, suggesting either local formation or selective deposition of immune complexes in the lower respiratory tract of some scleroderma patients.

Clinical utility of assays for circulating immune complexes

There are now many assays for the quantification of circulating immune complexes, each with distinct specificity and sensitivity. In a wide variety of rheumatic, infectious, neoplastic, and metabolic conditions, levels of circulating immune complexes may be elevated. In select situations, determination of circulating immune complex levels may help clinicians in the management of their patients. In lupus erythematosus, circulating immune complex levels, in conjunction with other immune parameters, may provide more insight into the disease course and activity than assessment of end organ parameters alone. In the differential diagnosis of infective endocarditis, serial levels of circulating immune complexes may provide evidence of effectiveness or failure of treatment. There is evidence that assays for circulating immune complexes may be of potential benefit in the management of Lyme disease and acute myelogenous leukemia.

Serum immune complexes in systemic sclerosis: relationship with precipitating nuclear antibodies

In a comparative study of antinuclear antibodies (ANA) and immune complexes in the serum of 43 patients with systemic sclerosis (SS) ANA were detected by indirect immunofluorescence on Hep 2 cells and/or double immunodiffusion in 90% of patients, while immune complex assays were positive in 32% of patients. The immune complex assays were positive only in sera containing antibodies to Scl 70, n-RNP, Ro, and La. The presence of immune complexes in SS sera is therefore related to ANA specificity. This might explain the variable findings of several previous studies of immune complexes in SS.

Immune complexes and antinuclear, antinucleolar, and anticentromere antibodies in scleroderma

Forty-one patients with various forms of systemic sclerosis (scleroderma) and positive antinuclear antibodies of nucleolar (ten patients), speckled (eleven patients), or centromere pattern (twenty patients) were selected for study of immune complexes by the radioisotope labeled Clq binding and the radioisotope labeled protein A binding methods. The presence of immune complexes was found by the Clq binding assay in sixteen patients (39%) and by a protein A binding assay in eight patients (20%). Overall, 46% of patients (19/41) had immune complexes. A lower incidence of organ involvement and fewer positive results in the screening of serum immune complexes were observed in patients with centromere antibody (35%) than in patients with nucleolar (60%) or speckled pattern (55%). Patients with immune complexes had higher frequencies of kidney, heart, and muscle involvement and digital ulceration than did patients with no detectable immune complexes, but the differences were not statistically significant. Diffuse skin involvement was not related to the presence of immune complexes.

Circulating immune complexes: their immunochemistry, biology, and detection in selected dermatologic and systemic diseases

Circulating immune complexes (CICs) are a heterogeneous group of immunoreactants formed by the noncovalent union of antigen and antibody. Many factors influence the formation, immunochemistry, biology, and clearance of these soluble reactants. The recent development of sensitive assays for the detection of CICs and the capability to assess immune complex (IC) clearance mechanisms in humans in vivo have expanded our understanding of these mediators. CICs influence both the afferent and efferent limbs of the immune response and can mediate tissue damage in certain pathologic states. ICs probably play an important role in the pathogenesis of serum sickness, systemic lupus erythematosus, and cutaneous necrotizing vasculitis. Recent investigations have raised the possibility that CICs may be of significance in other types of vasculitis as well. In other instances, ICs may form in response to tissue injury and subsequently modify the immune response of the host. A review of this material with special emphasis on diseases of relevance to dermatologists is presented.

Lowered angiogeneic capability of peripheral blood lymphocytes in progressive systemic sclerosis (scleroderma)

Peripheral blood lymphocytes isolated from 19 patients with progressive systemic sclerosis (7 with diffuse scleroderma and 12 with CREST syndrome) and from 19 healthy control individuals were tested in a lymphocyte-induced angiogenesis assay. The cells were injected intradermally into x-ray-immunosuppressed mice and their capability to induce new blood vessel formation was assessed by morphologic criteria. The lymphocytes derived from patients with systemic scleroderma showed a significant decrease in angiogeneic capability compared with controls. No significant difference in this capability was found between patients with diffuse scleroderma and those with CREST syndrome. The decrease in the angiogeneic capability of lymphocytes reflects a depression in cell-mediated immunity and might be relevant to the capillary loss observed in systemic scleroderma.