The value of complement activation products in the assessment of systemic lupus erythematosus flares

Serum RGC-32 in children with systemic lupus erythematosus

Childhood-onset systemic lupus erythematosus (SLE) can be more severe than adult patients. Early diagnosis and accurate evaluation of the disease are very important for the patients. Response gene to complement-32 (RGC-32) protein is the downstream regulator of C5b-9 complex which is the terminal pathway of complement activation. Complement system plays a very important role in the pathogenesis of SLE. RGC-32 in patients with SLE has not been reported yet. We aimed to examine the clinical value of RGC-32 in children with SLE. A total of 40 children with SLE and another 40 healthy children were enrolled for this study. Clinical data were obtained prospectively. Serum RGC-32 was determined by ELISA. We found that serum RGC-32 was significantly elevated in children with SLE than that in the healthy group. Serum RGC-32 was significantly higher in the children with moderately/severely active SLE than that in the children with no/mildly active SLE. Furthermore, serum RGC-32 level correlated positively with C-reactive protein, erythrocyte sedimentation rate and ferritin and correlated negatively with white blood cell counts and C3. RGC-32 may be involved in the pathogenesis of SLE. RGC-32 might become a good biomarker in the diagnosis and evaluation of SLE.

Measurement of Complement Activation via Plasma-Soluble C5b-9 Comparison with Terminal Complement Complex Staining in a Series of Kidney Biopsies

INTRODUCTION

With the emergence of therapeutic complement inhibitors, there is a need to identify patients with complement-driven inflammation. C5b-9 is the terminal product of the three complement pathways and therefore a marker of total complement activation. We present a pilot study which aims to assess whether plasma soluble C5b-9 (sC5b-9) correlates with terminal complement complex (TCC) staining in kidney tissue. The secondary aim was to assess the utility of plasma sC5b-9 as part of routine workup in kidney patients undergoing kidney biopsy.

METHODS

Thirty-seven patients undergoing kidney biopsy had plasma sC5b-9 and TCC staining on kidney tissue performed. Additional blood markers including creatinine, haemoglobin, CRP, factor H, factor I, and midkine levels were also taken. These parameters were correlated with the histological diagnoses. Patients were divided into a diseased group (n = 31) and a control group (n = 6) consisting of transplanted kidneys with minor or no changes. Of the biopsies in the control group, 50% were performed as per protocol, and the other 50% were performed due to clinical need.

RESULTS

There was no correlation found between plasma sC5b-9 and TCC kidney staining. Elevated sC5b-9 levels were found in a heterogeneous group of patients but were associated with higher CRP and lower haemoglobin levels. Overall, there was more TCC kidney staining in the diseased group compared with the control group, and a trend was observed of diabetic, primary membranous nephropathy, and amyloidosis patients having more intense glomerular and peritubular/interstitial staining.

CONCLUSION

Plasma sC5b-9 as a marker of total complement activation does not correlate with TCC kidney staining. This discordance suggests that plasma sC5b-9 and TCC staining are distinct markers of disease. TCC staining reflects chronicity and tissue deposition of complement over time. Conversely, plasma sC5b-9 concentrations change rapidly and reflect systemic complement activation. Complement activation was present in a heterogeneous group of kidney disease, indicating the underlying role of complement in many disorders.

Significance of urine complement proteins in monitoring lupus activity

Objectives

Complement activation is a critical feature in the development of systemic lupus erythematosus (SLE). Whether there are changes of complement components in the urine of SLE has not been reported. The aim of the study was to evaluate the complement-related proteins in the urine of SLE, verify differentially expressed proteins(DEPs) in the active phase of SLE, further explore their clinical application value.

Methods

First, we used bioinformatics and functional enrichment to screen and identify the urine protein profile of SLE patients. Then, analyzed and verified the proteins related to the complement pathway by western-blot and Parallel Reaction Monitoring (PRM) technology. Further evaluated the relationship between urinary DEPs related to complement pathway and disease activity.

Results

A total of 14 complement pathway-related proteins were screened for differences in expression between the active group and the stable group, eight of these DEPs were up-regulated and six were down-regulated. These DEPs may play a key role in SLE disease activity. We used PRM technology to verify the eight up-regulated proteins, and found that four of these complement proteins, namely C9, C8A, C4B, and C8G, were significantly increased in active group. Furthermore, these four DEPs were highly correlated with disease activity. In the urine of SLE patients, AUCs of 0.750, 0.840, 0.757 and 0.736 were achieved with C9, C8A, C4B, and C8G, respectively.

Conclusions

Complement-related DEPs in urine have a certain correlation with SLE disease activity. Urine C9, C8A, C4B and C8G present promising non-invasive biomarkers for monitoring lupus activity.

Urinary C3d is elevated in patients with active Lupus nephritis and a fall in its level after 3 months predicts response at 6 months on follow up

INTRODUCTION

Complement activation is central to the pathogenesis of lupus nephritis (LN). Low serum complement C3 and C4, are traditionally used as markers of lupus disease activity in general and LN in particular. In this study we prospectively measured plasma and urine C3d and C4d, degradation products of C3 and C4 corrected to creatinine in a cohort of biopsy proven LN in a longitudinal fashion for its correlation with disease activity.

METHODS

Twenty eight biopsy proven active lupus nephritis (AN) were recruited along with four inactive nephritis (IN) and 10 healthy controls (HC). Plasma and urine were collected at baseline, prior to induction treatment and 3 months later. Clinical measures of disease activity, Systemic lupus erythematosus disease activity index 2000 (SLEDAI 2K), renal SLEDAI, serum C3, C4 and antibodies to ds DNA, urine protein and creatinine excretion (UP/UC) were collected. Plasma and urine C3d and C4d were measured using ELISA and normalized to spot urine creatinine value.

RESULTS

Twenty eight AN of median age of 26.5 (20-31.50) years and disease duration of 3 (0.7-5) years were enrolled. The median urinary C3d/creatinine before treatment was 388.20 (48.98-1296) ng/mg which fell significantly to 62.69 (28.04-502.4) ng/mg at 3 months followup (p-0.01). The baseline values for the active renal disease was significantly different from IN group (9.9 (4.5-46.53 ng/mg) p-0.00). Treatment responders (partial and complete) at 6 months showed a significant fall in urinary C3d at 3 months whereas non responders had a non significant change in value. There was a significant correlation of urine C3d/creatinine with SLEDAI2K (r-0.433, p-0.00), renal SLEDAI (r-0.356, p-0.00), UP/UC ratio (r-0.489, p-<0.0001) but no significant correlation with C3 or C4. There was a significant fall in the median values of plasma C3d from 791.1 (516.0.00-1550.43) µg/ml to 338.52 (211.35-525.82) (p-0.00) µg/ml at the end of 3 months. The values showed a significant correlation with SLEDAI 2K, renal SLEDAI, UP/UC along with a significant negative correlation with C3 and C4.

CONCLUSION

Urinary C3d/creatinine levels and plasma C3d levels can be used as biomarker of disease activity and treatment response.

The receptor for advanced glycation end-products (RAGE) is an important pattern recognition receptor (PRR) for inflammaging

The receptor for advanced glycation end-products (RAGE) was initially characterized and named for its ability to bind to advanced glycation end-products (AGEs) that form upon the irreversible and non-enzymatic interaction between nucleophiles, such as lysine, and carbonyl compounds, such as reducing sugars. The concentrations of AGEs are known to increase in conditions such as diabetes, as well as during ageing. However, it is now widely accepted that RAGE binds with numerous ligands, many of which can be defined as pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The interaction between RAGE and its ligands mainly results in a pro-inflammatory response, and can lead to stress events often favouring mitochondrial dysfunction or cellular senescence. Thus, RAGE should be considered as a pattern recognition receptor (PRR), similar to those that regulate innate immunity. Innate immunity itself plays a central role in inflammaging, the chronic low-grade and sterile inflammation that increases with age and is a potentially important contributory factor in ageing. Consequently, and in addition to the age-related accumulation of PAMPs and DAMPs and increases in pro-inflammatory cytokines from senescent cells and damaged cells, PRRs are therefore important in inflammaging. We suggest here that, through its interconnection with immunity, senescence, mitochondrial dysfunction and inflammasome activation, RAGE is a key contributor to inflammaging and that the pro-longevity effects seen upon blocking RAGE, or upon its deletion, are thus the result of reduced inflammaging.

Association of Blood Concentrations of Complement Split Product iC3b and Serum C3 With Systemic Lupus Erythematosus Disease Activity

Objective

To examine correlations between blood levels of complement split product iC3b and serum component C3 with clinically meaningful changes in disease activity in patients with systemic lupus erythematosus (SLE).

Methods

A total of 159 consecutive patients with SLE, diagnosed according to the American College of Rheumatology or Systemic Lupus International Collaborating Clinics classification criteria, were enrolled in CASTLE (Complement Activation Signatures in Systemic Lupus Erythematosus), a prospective observational study. Patients with 1–7 study visits were included in this longitudinal analysis. In addition, 48 healthy volunteers were enrolled to establish a normal reference value for the ratio of blood iC3b to serum C3 concentrations. Serum C3 and C4 levels were measured by nephelometry, and blood iC3b levels were measured by a lateral flow assay. SLE disease activity was monitored with the Responder Index 50 instrument of the SLE Disease Activity Index 2000.

Results

Relative changes in the iC3b:C3 ratio, levels of anti–double‐stranded DNA (anti‐dsDNA) antibodies, and use of a supraphysiologic dose of prednisone (>7.5 mg/day) each independently correlated with SLE disease activity, as determined in multilevel multiple logistic regression analyses. Only the iC3b:C3 ratio was significantly associated with clinically meaningful improvements in disease activity among patients with SLE who were receiving a supraphysiologic dose of prednisone. The iC3b:C3 ratio outperformed C3 and C4 levels with regard to discriminating active SLE from inactive SLE, and major flares from no disease activity. The iC3:C3 ratio, anti‐dsDNA antibody levels, erythrocyte sedimentation rate, and use of a supraphysiologic prednisone dose were each independently associated with the presence of lupus nephritis, whereas none of these measures was associated with SLE rash. The association of the iC3b:C3 ratio with lupus nephritis was independent of other observed clinical manifestations.

Conclusion

The ratio of blood iC3b to serum C3 concentrations correlates with the extent of SLE disease activity and with clinically meaningful changes in disease activity in patients with SLE. Furthermore, the iC3b:C3 ratio may discriminate between active and inactive SLE, and between major flares and no active disease.

Glomerular membrane attack complex is not a reliable marker of ongoing C5 activation in lupus nephritis

Complement plays an important role in the pathogenesis of lupus nephritis (LN). With the emergence of therapeutic complement inhibition, there is a need to identify patients in whom complement-driven inflammation is a major cause of kidney injury in LN. Clinical and histopathological data were obtained retrospectively from 57 biopsies with class III, IV, and V LN. Biopsies were stained for complement components C9, C5b-9, C3c, and C3d and for the macrophage marker CD68. C9 and C5b-9 staining were highly correlated (r = 0.92 in the capillary wall). C5b-9 staining was detected in the mesangium and/or capillary wall of both active and chronic proliferative LN in all but one biopsy and in the capillary wall of class V LN in all biopsies. C5b-9 staining intensity in the tubular basement membrane correlated with markers of tubulointerstitial damage, and more intense capillary wall C5b-9 staining was significantly associated with nonresponse to conventional treatment. Glomerular C5b-9 staining intensity did not differ between active and chronic disease; in contrast, C3c and CD68 staining were associated with active disease. Evaluation of serial biopsies and comparison of staining in active and chronic LN demonstrated that C5b-9 staining persisted for months to years. These results suggest that C5b-9 staining is almost always present in LN, resolves slowly, and is not a reliable marker of ongoing glomerular C5 activation. This limits the utility of C5b-9 staining to identify patients who are most likely to benefit from C5 inhibition.

Flares in systemic lupus erythematosus: diagnosis, risk factors and preventive strategies

Despite advances in the treatment, patients with systemic lupus erythematosus (SLE) often experience disease exacerbations (flares) of varying severity. Their diagnosis is primarily made on clinical grounds after exclusion of other diseases or disturbances, primarily infections, and can be assisted by the use of validated clinical indices. Serological tests such as serum complement fractions and anti-dsDNA autoantibodies, are helpful in monitoring SLE activity, but they lack high diagnostic accuracy. Flares are more frequent in patients with persistent immunological and clinical activity, and have been described as significant risk factor for development of irreversible end-organ damage. Accordingly, prevention of flares has been recognized as a distinct therapeutic target in SLE and involves adequate control of disease activity, use of hydroxychloroquine, maintaining immunosuppressive or biologic therapy for several years, and avoiding non-compliance issues. The future holds promise for the discovery of biomarkers that will accurately predict or diagnose SLE flares, thus allowing for the implementation of patient-tailored preventive strategies.

Lupus nephritis biomarkers

Lupus nephritis (LN), a potentially destructive outcome of SLE, is a real challenge in the management of SLE because of the difficulty in diagnosing its subclinical onset and identifying relapses before serious complications set in. Conventional clinical parameters such as proteinuria, GFR, urine sediments, anti-dsDNA and complement levels are not sensitive or specific enough for detecting ongoing disease activity in lupus kidneys and early relapse of nephritis. There has long been a need for biomarkers of disease activity in LN. Such markers ideally should be capable of predicting early sub-clinical flares and could be used to gauge response to therapy, thus obviating the need for serial renal biopsies with their possible hazardous complications. Since urine can be readily obtained, it lends itself as an obvious biological substrate. In this review, the use of urine and serum as sources of lupus nephritis biomarkers is described, and the results of biomarker discovery studies using candidate and proteomic approaches are summarized.

Inhibition of terminal complement: a novel therapeutic approach for the treatment of systemic lupus erythematosus

The importance of the complement system in the pathophysiology of systemic lupus erythematosus (SLE) is clear although individual complement components play very different roles in the disease process. Early complement proteins are critical in the clearance of immune complexes and apoptotic bodies, and their absencepredisposesindividualsto SLE. Conversely, activationof terminalcomplement is associated with exacerbations of disease and damage to tissues and organs, particularly in lupus nephritis. Monoclonal antibodies that specifically inhibit terminal complement activation while preserving the critical functions of the early complement cascade have now been developed. These antibodies target the C5 complement protein, blocking its cleavage and the subsequent generation of potent proinflammatory molecules. Anti-C5 therapeutics have recently been investigated in an animal model of SLE and in a Phase I single dose study in humans. The results of these studiesand the multiple roles of complement in SLE are discussed.

Ethnic, clinical and immunological factors in systemic lupus erythematosus and the development of lupus nephritis: results from a multi-ethnic New Zealand cohort

The aim of this study was to identify risk factors for lupus nephritis including clinical, laboratory, and ethnic factors in a cohort of lupus patients in New Zealand. A retrospective study of patients from two teaching hospitals in Auckland, New Zealand. Patients were selected if they had attended as either an inpatient, or a rheumatology outpatient between 2000 and 2005. 170 patients had SLE according to ACR classification. Lupus nephritis (LN) was diagnosed according to ACR criteria. Clinical, laboratory, and ethnic data were gathered from the patient notes. Twenty-four patients had LN at diagnosis and 32 patients developed LN after diagnosis. LN was associated with serositis ( P = 0.008), cutaneous vasculitis ( P = 0.026), anaemia ( P = 0.005), CRP elevation >6 months ( P < 0.001), hypocomplementaemia >6 months ( P < 0.0001). Patients with elevated doublestranded DNA (dsDNA) (>5 × normal) were more likely to develop type IV LN ( P = 0.0096). Forty-one percent of patients were Caucasian, 12% Maori, 23% Pacific People, 16% Asian, 6% Indian. Maori patients with SLE (odds ratio (OR) = 8.47, 95% confidence interval (CI) = 2.11—33.96, P = 0.002), and Pacific People (OR = 3.11, 95% CI = 1.29—11.48, P = 0.014) had increased risk for developing LN. Anaemia at presentation (hazard ratio (HR) 3.2, 95% CI = 1.4—7.1, P = 0.004), and low complement >6 months (HR = 3.4, 95% CI = 1.4—8.7, P = 0.008) were independent risk factors for developing LN after SLE diagnosis. In New Zealand, Pacific People and Maori patients with SLE have a higher incidence of LN, and patients with anaemia and hypocomplementaemia are more likely to develop LN after diagnosis. Patients with high dsDNA levels are more likely to develop Type IV lupus nephritis. Lupus (2007) 16, 830—837.

New insights into complement: a mediator of injury and marker of disease activity in systemic lupus erythematosus

Studies performed during the past several decades have demonstrated a role for the complement system in both the etiology and pathogenesis of systemic lupus erythematosus (SLE). However the specifically defective molecular and cellular pathways responsible for the disease and its complications have generally not been identified. In this report, we describe two recent advances in complement pathobiology that highlight future directions for promising investigation toward enhancing our capacity to diagnose SLE, to monitor activity of the disease, and to identify molecular and cellular defects in SLE that can be targeted by therapeuticinhibitors of complement activation.In the first example, we describe recently developed assays to detect erythrocyte C4d and complement receptor1 for diagnosis and monitoring of disease activity in SLE. In the second example, we describe a recently discovered role for complement in mediating fetal loss in antiphospholipid syndrome and discuss the potential for this observation to facilitate identification and development of complement based biomarkers to predict poor fetal outcome in pregnant patients with SLE. These two examples are meant to underscore the importance of complement in the etiology and pathogenesis of SLE and its complications, and to stress the need for further investigation focused on the link between the complement system and SLE.

A quantitative lateral flow assay to detect complement activation in blood

Complement is a major effector arm of the innate immune system that responds rapidly to pathogens or altered self. The central protein of the system, C3, participates in an amplification loop that can lead to rapid complement deposition on a target and, if excessive, can result in host tissue damage. Currently, complement activation is routinely monitored by assessing total C3 levels, which is an indirect and relatively insensitive method. An alternative approach would be to measure downstream C3 activation products such as C3a and iC3b. However, in vitro activation can produce falsely elevated levels of these biomarkers. To circumvent this issue, a lateral flow immunoassay system was developed that measures iC3b in whole blood, plasma, and serum and avoids in vitro activation by minimizing sample handling. This assay system returns results within 15 min and specifically measures iC3b while having minimal cross-reactivity to other C3 split products. While evaluating the potential of this assay, it was observed that circulating iC3b levels can distinguish healthy individuals from those with complement activation-associated diseases. This tool is engineered to provide an improved method to assess complement activation at point of care and could facilitate studies to monitor disease progression in a variety of inflammatory conditions.

Use of biomarkers in the management of children with lupus

Childhood systemic lupus erythematosus (SLE) is known to have a worse prognosis than adult-onset disease, and monitoring and treatment of the disease are still a challenge. Thus, there is an urgent need for highly reliable, non-invasive biomarkers for early detection of relapses, to avoid long-term complications and to optimize the management of children with LN. Recent studies of pediatric patients have yielded novel specific biomarkers for SLE diagnosis which can be used for monitoring disease activity and response to treatment. The most promising biomarkers in juvenile-onset SLE include cell-bound complement activation products, some genomic profiles, and urinary proteins such as neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and alpha-1-acid glycoprotein. None of these might be suitable for use as a single SLE-biomarker. More likely a combination of novel biomarkers with traditionally used data, including autoantibodies and complement, might help to enhance sensitivity and specificity for early diagnosis, disease monitoring, and prediction of relapses.cp.

Noninvasive detection of complement activation through radiologic imaging

A wealth of experimental and clinical data demonstrates that the complement system is involved in the pathogenesis of numerous inflammatory diseases. Complement activation contributes to injury in disorders that involve nearly every tissue in the body. Concerted effort has been expended in recent years to develop therapeutic complement inhibitors. Eculizumab, an inhibitory antibody to C5, was recently approved for the treatment of several diseases, and many other complement inhibitors are in clinical development. As these drugs are developed, the need for improved methods of detecting and monitoring complement activation within particular tissues will be increasingly important. We have developed a magnetic resonance imaging (MRI)-based method for noninvasive detection of complement activation. This method utilizes iron-oxide nanoparticles that are targeted to sites of complement activation with a recombinant protein that contains the C3d-binding region of complement receptor (CR) 2. Iron-oxide nanoparticles darken (negatively enhance) images obtained by T2-weighted MRI. We have demonstrated that the CR2-targeted nanoparticles bind within the kidneys of mice with lupus-like kidney disease (MRL/1pr mice), causing a decrease in the T2 signal within the kidneys. This method discriminates diseased kidneys from healthy controls, and the magnitude of the negative enhancement in the cortex of MRL/lpr mice correlates with their disease severity. This method may be useful for identifying those patients most likely to benefit from complement inhibitors and for monitoring the response of these patients to treatment. These results may open up new avenues to develop tools for the monitoring of disease progression in complement-dependent diseases.

Biomarkers for systemic lupus erythematosus

In recent years, biomarkers have shown significant promise in helping decision-making in drug development. Systemic lupus erythematosus (SLE) is a complicated and highly heterogeneous disease that involves all organs. Only one drug, belimumab, has been approved by the US Food and Drug Administration to treat SLE during the last 50 years and there remains a high unmet medical need to develop new and effective therapies to benefit different patient populations in SLE. Due to the extreme heterogeneity of the disease and the complex and rigorous process to validate individual biomarkers, there is currently a very limited number of consensus biomarkers to aid the treatment decision-making in SLE. This review provides a snapshot of some biomarkers in the field that have the potential to make a big impact on drug development and/or treatment decisions by physicians. These include: type I interferon (IFN) gene signature as a pharmacodynamic marker and potential predictive marker for anti-type I IFN therapy; anti-double stranded DNA as a disease marker and potential predictive marker for flares; the complements and neutrophil signatures as disease marker of SLE; and TWEAK (a tumor necrosis factor family member produced by macrophages) and MCP-1 as potential markers to predict renal flares. Most of these markers need carefully planned and prospective studies with high statistical power to confirm their respective utilities. With the development and application of powerful new technologies, more successful biomarkers will emerge in SLE. This could improve the management of patients in the clinic and facilitate the development of novel and more effective therapeutics for this difficult-to-treat disease.

Therapeutic regulation of complement in patients with renal disease - where is the promise?

Numerous renal diseases are characterized by complement activation within the kidney, and several lines of evidence implicate complement activation as an important part of the pathogenesis of these diseases. Investigators have long anticipated that complement inhibitors would be important and effective therapies for renal diseases. Eculizumab is a monoclonal antibody to the complement protein C5 that has now been administered to patients with several types of renal disease. The apparent efficacy of this agent may herald a new era in the treatment of renal disease, but many questions about the optimal use of therapeutic complement inhibitors remain. Herein we review the rationale for using complement inhibitors in patients with renal disease and discuss several drugs and approaches that are currently under development.

Cell-bound complement biomarkers for systemic lupus erythematosus: from benchtop to bedside

Systemic lupus erythematosus is arguably the most clinically and serologically diverse autoimmune disease. This article highlights the biomarkers helpful in diagnosing this disease. The authors' own research is presented.

Lymphocyte-bound complement activation products as biomarkers for diagnosis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is frequently misdiagnosed due to the lack of definitive diagnostic tests. The purpose of this study was to determine specifically whether complement activation products (CAP) are deposited on lymphocytes of SLE patients and whether lymphocyte-bound CAP (LB-CAP) may serve as novel biomarkers for the diagnosis of SLE. We conducted a cross-sectional study of 224 patients with SLE, 179 patients with other diseases, and 114 healthy controls. LB-CAP on peripheral blood lymphocytes was measured by flow cytometry. Diagnostic utility of LB-CAP was determined by receiver operating characteristic (ROC) analysis. Significantly elevated levels of C4d and C3d were detected specifically on T and B lymphocytes (designated T-C4d, T-C3d, B-C4d, and B-C3d) of SLE patients. As diagnostic tools, T-C4d and B-C4d, respectively, were 56% sensitive/80% specific and 60% sensitive/82% specific in differentiating SLE from other diseases. Moreover, compared with measurement of anti-dsDNA, serum C3, or serum C4, measurement of T-C4d/B-C4d was significantly more sensitive in identifying SLE patients during a single clinic visit. This is the first investigation of lymphocytes bearing complement activation products in human disease. T-C4d and B-C4d have high diagnostic sensitivity and specificity for SLE and may have added value to current laboratory tests for SLE diagnosis.

USEFULNESS OF COMPLEMENT SPLIT PRODUCT, Bb, AS A CLINICAL MARKER FOR DISEASE ACTIVITY OF LUPUS NEPHRITIS

To evaluate the usefulness of Bb, a split product of complement factor B, as a clinical marker for disease activity of lupus nephritis, we measured the Bb concentration of sera from 42 patients with lupus nephritis. Serum Bb levels were significantly higher in patients with active nephritis (active nephritis group, n= 30) than in patients with nephritis in remission (remission group, n=12) (14.3+/-8.3 versus 7.4+/-5.9 microg/ml; p = 0.012). In contrast, there was no significant difference in serum C3 levels between active nephritis group and remission group (42.5+/-20.9 versus 44.7+/-15.9 mg/dl ; p = 0.77). In the comparison of Bb levels between active nephritis group and remission group, the sensitivity was 66.6%, specificity was 83.3%, and the positive and negative likelihood ratios were 3.95% and 0.41%, respectively. The present results suggest that serum Bb level is a useful clinical marker for disease activity in lupus nephritis.

Biomarkers for systemic lupus erythematosus: a review and perspective

PURPOSE OF REVIEW

Despite decades of extensive work in the understanding of the etiopathogenesis of systemic lupus erythematosus, few biomarkers have been validated and widely accepted for this disease. The lack of reliable, specific biomarkers not only hampers clinical management of systemic lupus erythematosus but also impedes development of new therapeutic agents. This paper reviews briefly the historical aspects of systemic lupus erythematosus biomarkers and summarizes recent studies on candidate biomarkers.

RECENT FINDINGS

Recognizing the urgent need for lupus biomarkers, a Lupus Biomarker Working Group has recently been initiated to facilitate collaborative efforts aimed at identifying and validating biomarkers for systemic lupus erythematosus. Based on available data, several laboratory markers have shown promise as biomarkers for susceptibility, diagnosis, and disease activity. These include Fc receptor genes (disease susceptibility), complement C4d-bound erythrocytes (diagnosis or disease activity), CD27 plasma cells (disease activity), 'interferon signature' (disease activity), and anti-C1q antibodies (disease activity and organ involvement).

SUMMARY

There is a longstanding and recently rejuvenated enthusiasm for biomarkers that precisely and specifically reflect the pathophysiologic and clinical changes in systemic lupus erythematosus. Promising candidate biomarkers have been identified but must still be validated through rigorous, large-scale multicenter studies.

Hypocomplementemia in systemic lupus erythematosus and primary antiphospholipid syndrome: prevalence and clinical significance in 667 patients

The objective of the study was to analyse the prevalence and clinical significance of hypocomplementemia in a large series of patients diagnosed either with systemic lupus erythematosus (SLE) or with primary antiphospholipid syndrome (APS) and its association with the main clinical, hematological and immunological features of these diseases. Between 1992 and 2003, complement determinations (C3 and C4 levels, CH50 activity) were performed in 597 consecutive patients diagnosed with SLE (530 women and 67 men, mean age 32.6 years) and 70 with primary APS (57 women and 13 men, mean age 38.7) visited in our department. Complement determinations are routinely made at the first visit of patients and yearly during the follow-up. SLE and primary APS were diagnosed according to current classification criteria. Hypocomplementemia was detected in 371 (62%) of SLE patients. Compared with patients with normal complement values, those with hypocomplementemia showed a higher prevalence of female gender (P < 0.001), fever (P = 0.021), nephropathy (P < 0.001), cutaneous vasculitis (P = 0.023), positive anti-dsDNA antibodies (P = 0.012) and cryoglobulinemia (P < 0.001). In addition, patients with hypocomplementemia showed a higher prevalence of APS-related features such as hemolytic anemia (P = 0.001) and antiphospholipid antibodies (P < 0.001). Hypocomplementemia was prospectively related to accumulated hospitalization in SLE patients but not with the accumulated number of lupus flares or with the survival after follow-up of five years. In contrast, 33 (47%) patients with primary APS presented low complement values, which were associated with a higher prevalence of livedo reticularis (P = 0.022), thrombocytopenia (P = 0.004), lupus anticoagulant (P = 0.013), positive IgM-aCL (P = 0.039), positive ANA (P = 0.002) and anti-dsDNA (P = 0.046). The diagnostic value of hypocomplementemia in patients with SLE is based on the association with disease activity, immune-complex mediated manifestations (glomerulonephritis, cryoglobulinemia) and APS-related features (livedo reticularis, hemolytic anemia and aPL). Hypocomplementemia was found in nearly half of patients with primary APS, and was associated with some APS features (livedo reticularis, thrombocytopenia, aPL) but also with SLE-related immunological markers (ANA and anti-dsDNA), identifying a subset of patients with primary APS with a higher risk of evolving to SLE. These results clearly support the routine determination of complement factors in the clinical follow-up of patients with SLE and primary APS.

New advances in measurement of complement activation: lessons of systemic lupus erythematosus

Activation of the complement system plays a fundamental role in the pathogenesis of systemic lupus erythematosus (SLE). For the past several decades, quantifying this process has focused primarily on determination of serum C3 and C4, although the utility of these assays for diagnosis and monitoring disease activity is still debated. During this same timespan, knowledge of the complement system has exploded, with identification of more than 30 proteins, an abundance of newly recognized functions, and even a third pathway of activation. These advances suggest that it is appropriate to revisit the complement system as a potential source of biomarkers for SLE. This paper reviews briefly the role of complement in SLE and other inflammatory diseases, discusses conventional methods for complement measurement and their drawbacks, and focuses on recent advancements in harnessing the complement system for monitoring SLE. Specifically, novel assays that measure cell-bound complement activation products are introduced and their utility as biomarkers of SLE disease activity is discussed.

Pathological study on the relationship between C4d, CD59 and C5b-9 in acute renal allograft rejection

In order to evaluate the activation or inhibition of the later phases of classical complement cascade in renal allograft presenting with acute rejection, particularly with C4d deposition on the peritubular capillary (PTC), we observed the expression of CD59 and C5b-9 on the PTC. Subjective cases were divided into two groups, an acute rejection group, of 4 males and 6 females, and a normal donor group, of 5 males and 5 females. Renal biopsies were performed at the onset of acute rejection and at the transplant operation, before reperfusion. C4d deposition on PTC was found in three of 10 cases (30%) with biopsy proven acute rejection, whereas CD59 on PTC was positively expressed in all of the rejection cases. Although C5b-9 was not observed on PTC in the acute rejection group, it was intensively deposited on the tubular basement membrane (TBM) in five cases, including the three with positive C4d on PTC. In the normal donor group, CD59 on PTC was intensively observed, whereas C5b-9 was weakly expressed on TBM. CD59, a complement regulatory factor, works as an inhibitory factor against the formation of C5b-9, a membrane attack complex. From our data, we noted the dissociation between the depositions of C4d and C5b-9 on PTC. The substantially expressed CD59 on PTC may affect this dissociation between C4d and C5b-9 on PTC. The intensive deposition of C5b-9 on TBM in acute rejection cases may suggest an independent immunological injury attacking tubular cells.

Pre-neutralization of C5a-mediated effects by the monoclonal antibody 137-26 reacting with the C5a moiety of native C5 without preventing C5 cleavage

Complement C5a is aetiologically linked to inflammatory tissue damage in conditions like septicaemia, immune complex diseases and ischaemia-reperfusion injury. We here describe a monoclonal antibody (mAb), 137-26, that binds to the C5a moiety of human C5 and neutralizes the effects of C5a without interfering with C5 cleavage and the subsequent formation of lytic C5b-9 complex. Mouse anti-human C5 mAbs were generated and the reactivity with C5 and C5a was detected by ELISA and surface plasmon resonance. The inhibition of C5a binding to C5a receptor was studied using a radioligand binding assay. The effects of the antibody on C5a functions were examined using isolated neutrophils and a novel human whole blood model of inflammation. Haemolytic assays were used to study the effect on complement-mediated lysis. mAb 137-26 reacted with both solid- and solution-phase C5 and C5a in a dose-dependent manner with high affinity. The antibody competed C5a binding to C5a receptor and inhibited C5a-mediated chemotaxis of neutrophils. Furthermore, the antibody effectively abrogated complement-dependent E. coli-induced CD11b up-regulation and oxidative burst in neutrophils of human whole blood. mAb 137-26 was more potent than a C5a receptor antagonist and a previously described anti-C5a antibody. mAb 137-26 did not inhibit complement-mediated lysis, nor did it activate complement itself. Together, mAb 137-26 binds both the C5a moiety of native C5 and free C5a, thereby effectively neutralizing the biological effects of C5a. The antibody may have therapeutic potential in inflammatory diseases where C5a inhibition combined with an operative lytic pathway of C5b-9 is particularly desired.

Complement and systemic lupus erythematosus

Complement is implicated in the pathogenesis of systemic lupus erythematosus (SLE) in several ways and may act as both friend and foe. Homozygous deficiency of any of the proteins of the classical pathway is causally associated with susceptibility to the development of SLE, especially deficiency of the earliest proteins of the activation pathway. However, complement is also implicated in the effector inflammatory phase of the autoimmune response that characterizes the disease. Complement proteins are deposited in inflamed tissues and, in experimental models, inhibition of C5 ameliorates disease in a murine model. As a further twist to the associations between the complement system and SLE, autoantibodies to some complement proteins, especially to C1q, develop as part of the autoantibody response. The presence of anti-C1q autoantibodies is associated with severe illness, including glomerulonephritis. In this chapter the role of the complement system in SLE is reviewed and hypotheses are advanced to explain the complex relationships between complement and lupus.

A decrease in complement is associated with increased renal and hematologic activity in patients with systemic lupus erythematosus

OBJECTIVE

To determine the degree to which changes in C3 and C4 precede or coincide with changes in systemic lupus erythematosus (SLE) activity, as measured by 5 global activity indices, the physician's global assessment (PGA), modified SLE Disease Activity Index (M-SLEDAI), modified Lupus Activity Index (M-LAI), Systemic Lupus Activity Measure (SLAM), and the modified British Isles Lupus Assessment Group (M-BILAG), and to evaluate the association between changes in C3 and C4 levels and SLE activity in individual organ systems.

METHODS

Fifty-three lupus patients were observed monthly for 1 year in a longitudinal study. Lupus disease activity and complement levels were measured at each visit. Lupus flare was defined as a 1.0 (or greater) increase in the PGA, a 3-point increase in the M-SLEDAI, a 0.1 increase in the M-LAI, a 3-point increase in the SLAM, or a 4-point increase in the M-BILAG within a 1-month period. Flare rates were calculated for subgroups defined by previous (1 month before) or concurrent changes in complement levels. Logistic regression models were used to determine the significance of the association between recent changes in complement levels and flare, controlling for prednisone dosage. Similar models were used to assess the association between changes in C3 or C4 levels and increased SLE activity in specific organ systems.

RESULTS

Lupus flares occurred at 12% of visits based on the PGA, 19% based on the M-SLEDAI, 25% based on the M-LAI, 13% based on the SLAM, and 12% based on the M-BILAG. Recent changes in C3 and C4 levels were not associated with flares based on 3 of the 5 activity indices. Flares defined by the M-LAI were more frequent when there was a concurrent decrease in C3 (odds ratio [OR] 1.9, 95% confidence interval [95% CI] 1.1-3.1) or C4 (OR 2.1, 95% CI 1.3-3.6). Higher flare rates, as defined by the SLAM, were associated with previous increases in C3 (OR 1.6, 95% CI 1.0-2.6) and C4 (OR 2.2, 95% CI 1.2-3.9). When individual organ systems were analyzed, decreases in C3 and C4 were associated with a concurrent increase in renal disease activity (OR 2.2, 95% CI 1.4-3.5 and OR 1.9, 95% CI 1.1-3.4, respectively). Decreases in C3 were also associated with concurrent decreases in the hematocrit (OR 4.6, 95% CI 1.7-12.3), platelet (OR 2.5, 95% CI 1.5-4.1), and white blood cell (OR 2.2, 95% CI 1.3-3.6) counts. Previous increases in C3 levels were associated with a decrease in platelets (OR 1.7, 95% CI 1.1-2.7). A decrease in C4 was associated with a concurrent decrease in the hematocrit level (OR 3.2, 95% CI 1.3-7.5) and platelet count (OR 1.6, 95% CI 1.0-2.5).

CONCLUSION

Decreases in complement levels were not consistently associated with SLE flares, as defined by global measures of disease activity. However, decreasing complement was associated with a concurrent increase in renal and hematologic SLE activity.

Measurement of intracellular interferon-gamma and interleukin-4 in whole blood T lymphocytes from patients with systemic lupus erythematosus

Contradictory data are available about the dominance of T-helper 1 (T(H)1), or T-helper 2 (T(H)2) cytokines in systemic lupus erythematosus (SLE). Therefore, intracellular interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) production of T lymphocytes was measured in whole blood of healthy donors and active and inactive SLE patients by flow cytometry. The percentage of IFN-gamma and IL-4 positive cells was low (<1%) in unstimulated samples of the healthy controls, while that of IFN-gamma and IL-4 positive cells in the stimulated cells was 25.2+/-10.6% and 0.6+/-1.5%, respectively. No significant difference was found between SLE patients and healthy controls and between active and inactive patients in these parameters either in the unstimulated or in the stimulated samples. One patient with severe disease had as high as 11.8% IL-4 positive cells and 12.5% IFN-gamma positive cells in the stimulated samples, but after the initiation of intensive corticosteroid and cytostatic therapy, the percentage of IL-4 positive T cells decreased (4.76%) while that of IFN-gamma positive T cells increased (47.91%). We conclude that the intracellular IL-4 and IFN-gamma expression of T lymphocytes does not differ markedly between SLE patients and healthy controls, with the possible exception of severe disease, when marked IL-4 overproduction may exist beside low IFN-gamma production. Furthermore, corticosteroid and cytostatic therapy might normalize this altered IFN-gamma/IL-4 ratio.

Usefulness of detection of complement activation products in evaluating SLE activity

Complement activation products, such as C1rs-C1inh, specific for the activation of the classical pathway, C3b(Bb)P, specific for the activation of the alternative pathway and SC5b-9, specific for common terminal pathway of the complement cascade, were measured in healthy donors and in patients with clinically active and inactive systemic lupus erythematosus (SLE). Plasma levels of C3b(Bb)P and SC5b-9 were moderately, those of C1rs-C1inhibitor (C1rs-C1inh) were markedly elevated in patients with clinically inactive SLE, compared with healthy controls. The difference between active and inactive stages of the disease was best reflected by C3b(Bb)P plasma concentration (P<0.001), which also showed the highest correlation with the SLEDAI (Rs=0.41 P<0.001) and which was the most useful in distinguishing active and inactive sample pairs as well. The difference between SC5b-9 levels in the active and inactive stages was also significant (P=0.007), while that of C1rs-C1inh did not differ significantly (P=0.136). The correlation of the SLEDAI with SC5b-9 was 0.3 (P=0.015), while with C1rs-C1inh it was 0.21 (P=0. 089). These findings suggest that the measurement of complement activation products, especially that of the alternative pathway, are sensitive markers of the activity of SLE and can be used for clinical purposes.

Dehydroepiandrosterone and biologics in the treatment of systemic lupus erythematosus

Our understanding of the immune system in health and disease has greatly increased over this past decade. An outgrowth of this burgeoning knowledge has been the discovery of novel strategies to treat a variety of autoimmune diseases. As a result, significant advances have been made in the treatment of arthritis with a half-dozen new treatments approved between September, 1998 and November, 1999. Although no new therapies have been approved for the treatment of systemic lupus erythematosus (SLE), this decade has witnessed an unprecedented amount of activity in drug development for this disease. This article specifically addresses the current status of drug development in the area of hormonal and biologic therapies for SLE.

Complement activation in patients with systemic lupus erythematosus without nephritis

OBJECTIVE

To study the association between disease activity and complement activation prospectively in patients with systemic lupus erythematosus (SLE).

PATIENTS AND METHODS

Twenty-one SLE patients were examined monthly for 1 yr. Disease activity, autoantibodies, conventional complement tests and the following complement activation products were investigated: C1rs-C1inh complexes, C4bc, Bb, C3a, C3bc, C5a and the terminal SC5b-9 complement complex (TCC).

RESULTS

Modest variation in disease activity was noted. None of the patients had nephritis. Flare was observed at 27 visits. Four patients had anti-C1q antibodies in conjunction with modestly low C1q concentrations. The complement parameters were rather constant during the observation period. Slightly to moderately decreased C4 (0.05-0.10 g/l) was found in 10 patients and severely decreased C4 (<0.05 g/l) in seven patients. Decreased C4 was not associated with increased complement activation. Complement activation products were either normal or slightly elevated. TCC was the only activation product correlating significantly with score for disease activity at flare. None of the variables tested predicted flares.

CONCLUSION

Complement tests are of limited importance in routine examination of SLE without nephritis, although TCC is suggested to be one of the most sensitive markers for disease activity.

A critical evaluation of the putative role of C3adesArg (ASP) in lipid metabolism and hyperapobetalipoproteinemia

The acylation stimulating protein, ASP is a small, basic serum protein capable of stimulating triglyceride synthesis in cultured fibroblasts and adipocytes. Sequence analysis of ASP has shown that ASP is identical to C3adesArg the inactive fragment of the complement anaphylatoxin peptide, C3a. It has been proposed that C3adesArg (ASP) can be generated by mature adipocytes secreting the three complement proteins: complement protein C3, factor B and factor D (adipsin). There have also been indications that adipocytes may express a specific C3adesArg (ASP)-receptor that is distinct from the recently cloned C3a-receptor. This suggests that C3adesArg (ASP) acts as an adipocyte autocrine and that it plays a central role in the metabolism of adipose tissue. Based on these observations a hypothesis for the etiology of hyperapobetalipoproteinemia (hyperapoB) has been proposed. Hyperapobetalipoproteinemia (hyperapoB), is a familial lipoprotein disorder characterized by increased hepatic secretion of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) particles. If C3adesArg (ASP) function in the adipose tissue is impaired, a reduced rate of triglyceride synthesis will follow, generating an increased flux of fatty acids to the liver. In response to an increased flow of fatty acids, the liver will increase its production of VLDL particles yielding the phenotype of hyperapoB. This review critically assesses this hypothesis and the potential role of C3adesArg (ASP) as a major determinant for triglyceride synthesis in the light of data collected in vitro and in vivo.

An echocardiographic study of valvular heart disease associated with systemic lupus erythematosus

BACKGROUND

Valvular heart disease is the most important cardiac manifestation of systemic lupus erythematosus. We performed a study to determine the relation of valvular disease to other clinical features of lupus, whether or not the valve disease progresses, and the associated morbidity and mortality.

METHODS

We performed transesophageal echocardiography and rheumatologic evaluations in 69 patients with systemic lupus erythematosus. The echocardiographic findings were compared with those in 56 healthy volunteers. Fifty-eight patients (84 percent) had second evaluations a mean (+/-SD) period of 29 +/- 13 months later. The patients and controls were followed for 57 months.

RESULTS

Valvular abnormalities were common on the initial and the follow-up echocardiograms (in 61 and 53 percent of the patients, respectively). Valvular thickening was the predominant finding initially and on follow-up (in 51 and 52 percent of the patients, respectively), followed by vegetations (in 43 and 34 percent), valvular regurgitation (in 25 and 28 percent), and stenosis (in 4 and 3 percent). Valvular abnormalities frequently resolved, appeared for the first time, or persisted but changed in appearance or size between the two studies. Mild or moderate valvular regurgitation did not progress to become severe, and new stenoses did not develop. Neither the presence of valvular disease nor changes in the echocardiographic findings were temporally related to the duration, activity, or severity of lupus or to its treatment. The combined incidence of stroke, peripheral embolism, heart failure, infective endocarditis, and the need for valve replacement was 22 percent in the patients with valvular disease, but only 8 percent in those without it. A total of seven patients died during follow-up, in most cases as a result of valvular disease. Valvular abnormalities and complications were uncommon in the controls (occurring in 9 and 2 percent, respectively).

CONCLUSIONS

Valvular heart disease is common in patients with systemic lupus erythematosus, frequently changes over time, appears to be temporally unrelated to other clinical features of lupus, and is associated with substantial morbidity and mortality.

Sensitivity and specificity of plasma and urine complement split products as indicators of lupus disease activity

OBJECTIVE

To determine if measurement of serum complement split products (C4d, Bb, C5b-9) is better than conventional C3 and C4 measurements in distinguishing patients with varying degrees of lupus disease activity, and to determine if the presence of C3d in urine is helpful in distinguishing lupus patients with from those without early lupus nephritis.

METHODS

Lupus disease activity was prospectively determined at 3 consecutive visits an average of 4 months apart, using the Systemic Lupus Activity Measure (SLAM), the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), and physician global assessment (PGA). Blood samples were evaluated for the presence of C4d, Bb, and C5b-9 by quantitative microassay plate enzyme immunoassay at each patient visit. We characterized urinary excretion of C3 fragments (with attention to C3d) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Western blotting.

RESULTS

Thirty-one SLE patients were enrolled in the study. The mean SLAM score and the mean SLEDAI score each correlated well with the PGA at all 3 visits. A SLAM score of 6 and a SLEDAI score of 4 had the best overall sensitivity and specificity for predicting moderate-to-severe disease activity by PGA (100% and 73%, respectively, for the SLAM and 86% and 94%, respectively, for the SLEDAI). Serum C4d and Bb were more sensitive indicators of current moderate-to-severe lupus disease activity at all 3 visits than were serum C5b-9, C3, and C4. C3 and C4 were more specific indicators of moderate-to-severe disease activity. Serum C4d and Bb were more sensitive at predicting moderate-to-severe disease activity at subsequent visits than were C5b-9, C3, and C4. Urine C3d was better than C3, plasma C4d, Bb, C5b-9 and anti-double-stranded DNA antibody in distinguishing patients with from those without acute lupus nephritis (P = 0.02).

CONCLUSION

C4d and Bb are sensitive indicators of moderate-to-severe lupus disease activity and may be most helpful in situations where conventional measurements are not, such as in lupus patients whose C3 and C4 levels remain normal despite evidence of clinical disease activity. It appears from this study that detection of urine C3d may be a simple way of measuring complement activation in the setting of lupus renal disease. The availability of instruments for clinical disease activity measurement such as the SLAM and the SLEDAI may enable more consistent definition of lupus disease activity and may thus provide a means for better examining the role of complement activation products in predicting lupus disease activity in larger patient populations.

Inherited deficiencies of complement in rheumatic diseases

Inherited complement deficiencies are rare but occur with increased frequency in systemic lupus erythematosus. This selective review summarizes the fundamentals of complement activation and biology and focuses on recent findings. system lupus erythematosus is highly associated with homozygous C1q deficiencies and with C4A null allotypes, and homozygous C2 and C3 deficiencies are less uniformly associated with autoimmune disease. This hierarchy of disease associations suggests the importance of an intact early classic activation pathway in preventing systemic lupus erythematosus. Assays of complement activation products may have greater sensitivity and specificity for systemic lupus erythematosus disease activity and lupus flares.