Cell-bound Complement Activation Products Research Articles

Cell-bound complement activation products in antiphospholipid antibody-positive patients without other systemic autoimmune rheumatic diseases

The objective of this study was to analyze complement activation in antiphospholipid antibody (aPL)-positive patients without other systemic autoimmune rheumatic diseases, using C3/C4 and cell-bound complement activation products (CB-CAPs) (B-lymphocytes [BC4d], erythrocytes [EC4d], and platelets [PC4d]). Persistently aPL-positive patients with or without aPL-related clinical manifestations (thrombotic APS [TAPS], microvascular APS [MAPS], obstetric APS, thrombocytopenia [TP], and/or hemolytic anemia [HA]) were enrolled in a single center study. Blood and clinical data were collected at baseline; a subgroup of patients completed 6- or 12-month follow-up. At baseline, 4/31 (13%) patients had decreased C3/C4, while 7/29 (24%) had elevated BC4d, 11/33 (33%) EC4d, and 12/32 (38%) PC4d. Based on different aPL profiles, all patients with decreased C3/C4 or elevated BC4d, EC4d, and PC4d had triple aPL or isolated lupus anticoagulant positivity. Based on different aPL clinical phenotypes, the number of patients with strongly positive EC4d and PC4d were proportionally higher in those with MAPS/TP/HA, compared to TAPS or no APS. Compared to baseline, the frequencies of BC4d, EC4d, and PC4d positivity were not significantly different in the subgroup of patients during their 6- or 12-month follow-up. There was a weak correlation between C3/C4 and CB-CAPs, especially for PC4d. In summary, complement activation in aPL-positive patients varies based on aPL profiles and clinical phenotypes. Given the higher percentage of aPL-positive patients with abnormal CB-CAPs, compared to C3/C4, and the poor inverse correlation between CB-CAPs and C3/C4, our study generates the hypothesis that CB-CAPs have a role in assessing disease activity and thrombosis risk in aPL-positive patients.

Earlier vs. later time period of COVID-19 infection and emergent autoimmune signs, symptoms, and serologies

ObjectiveAutoantibodies and autoimmune diseases after SARS-CoV-2 infection are widely reported. Given evolving variants, milder infections, and increasing population vaccination, we hypothesized that SARS-CoV-2 infection earlier in the pandemic would be associated with more autoimmune connective tissue disease (CTD) symptoms and immunologic abnormalities. MethodsPatients ≥18 years old with COVID-19 3/1/2020-8/15/2022 completed the CTD Screening Questionnaire and were tested for 27 autoimmune serologies, SARS-CoV-2 serologies, cell-bound complement activation products (CB-CAPs), and T and B lymphocyte immunophenotypes by flow cytometry. We assessed relationships between symptoms, serologies, and immunophenotypes in earlier (3/1/2020-1/31/2021) vs. later (2/1/2021-8/15/2022) periods, with different predominating SARS-CoV-2 viruses. Results57 subjects had earlier and 23 had later pandemic COVID-19. 35 % of earlier vs. 17 % of later pandemic patients had CTD symptoms (p 0.18). More patients were antinuclear antibody (ANA) positive (44 % vs. 13 %, p 0.01) and had lupus anticoagulant (11 % vs. 4 %, p 0.67). After adjustment for age, race, and sex, earlier (vs. later) COVID-19 was associated with increased ANA positivity (OR 4.60, 95%CI 1.17, 18.15). No subjects had positive CB-CAPs. T and B cell immunophenotypes and SARS-CoV-2 serologies did not differ by group. In heatmap analyses, higher autoantibody variety was seen among those with infection in the early pandemic. ConclusionIn this sample, having COVID-19 infection in the earlier (pre-2/1/2021) vs. later pandemic was associated with more CTD symptoms, ANA positivity, and autoantibody reactivities. Earlier SARS-CoV-2 variants circulating in a less vaccinated population with less natural immunity may have been more immunogenic.

Complement as a Biomarker for Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a disease of immune complex deposition; therefore, complement plays a vital role in the pathogenesis of SLE. In general, complement levels in blood and complement deposition in histological tests are used for the management of SLE. Thus, the evaluation of complement status can be useful in the diagnosis of SLE, assessment of disease activity, and prediction of treatment response and prognosis. In addition, novel complement biomarkers, such as split products and cell-bound complement activation products, are considered to be more sensitive than traditional complement markers, such as serum C3 and C4 levels and total complement activity (CH50), which become more widely used. In this review, we report the complement testing in the management of SLE over the last decade and summarize their utility.

A multianalyte assay panel with cell-bound complement activation products demonstrates clinical utility in systemic lupus erythematosus

ObjectiveTo evaluate the clinical utility of the multianalyte assay panel (MAP), commercially known as AVISE Lupus test (Exagen Inc.), in patients suspected of SLE.MethodsA systematic review of medical records of...

A Multianalyte Assay Panel With Cell‐Bound Complement Activation Products Predicts Transition of Probable Lupus to American College of Rheumatology–Classified Lupus

ObjectiveTo evaluate the usefulness of biomarkers to predict the evolution of patients suspected of systemic lupus erythematosus (SLE), designated as probable SLE (pSLE), into classifiable SLE according to the American College of Rheumatology (ACR) classification criteria.MethodsPatients suspected of SLE were enrolled by lupus experts if they fulfilled three ACR criteria for SLE and were followed for approximately 1‐3 years to evaluate transition into ACR‐classifiable SLE. Individual cell‐bound complement activation products (CB‐CAPs), serum complement proteins (C3 and C4), and autoantibodies were measured by flow cytometry, turbidimetry, and enzyme‐linked immunosorbent assay, respectively. Blood levels of hydroxychloroquine (HCQ) were measured by mass spectrometry. A multianalyte assay panel (MAP), which includes CB‐CAPs, was also evaluated. A MAP of greater than 0.8 reflected the optimal cutoff for transition to SLE. Time to fulfillment of ACR criteria was evaluated by Kaplan‐Meier analysis and Cox proportional hazards model.ResultsOf the 92 patients with pSLE enrolled, 74 had one or two follow‐up visits 9‐35 months after enrollment for a total of 128 follow‐up visits. Overall, 28 patients with pSLE (30.4%) transitioned to ACR‐classifiable SLE, including 16 (57%) in the first year and 12 (43%) afterwards. A MAP score of greater than 0.8 at enrollment predicted transition to classifiable SLE during the follow‐up period (hazard ratio = 2.72; P = 0.012), whereas individual biomarkers or fulfillment of Systemic Lupus International Collaborating Clinics criteria did not. HCQ therapy was not associated with the prevention of transition to SLE.ConclusionApproximately one‐third of patients with pSLE transitioned within the study period. MAP of greater than 0.8 predicted disease evolution into classifiable SLE.

Cell-bound complement activation products associate with lupus severity in SLE

ObjectivesTo evaluate the association between lupus severity and cell-bound complement activation products (CB-CAPs) or low complement proteins C3 and C4.MethodsAll subjects (n=495) fulfilled the American College of Rheumatology (ACR) classification...

Complement Activation in Patients With Probable Systemic Lupus Erythematosus and Ability to Predict Progression to American College of Rheumatology-Classified Systemic Lupus Erythematosus.

ObjectiveTo evaluate the frequency of cell‐bound complement activation products (CB‐CAPs) as a marker of complement activation in patients with suspected systemic lupus erythematosus (SLE) and the usefulness of this biomarker as a predictor of the evolution of probable SLE into SLE as classified by the American College of Rheumatology (ACR) criteria.MethodsPatients in whom SLE was suspected by lupus experts and who fulfilled 3 ACR classification criteria for SLE (probable SLE) were enrolled, along with patients with established SLE as classified by both the ACR and the Systemic Lupus International Collaborating Clinics (SLICC) criteria, patients with primary Sjögren's syndrome (SS), and patients with other rheumatic diseases. Individual CB‐CAPs were measured by flow cytometry, and positivity rates were compared to those of commonly assessed biomarkers, including serum complement proteins (C3 and C4) and autoantibodies. The frequency of a positive multianalyte assay panel (MAP), which includes CB‐CAPs, was also evaluated. Probable SLE cases were followed up prospectively.ResultsThe 92 patients with probable SLE were diagnosed more recently than the 53 patients with established SLE, and their use of antirheumatic medications was lower. At the enrollment visit, more patients with probable SLE were positive for CB‐CAPs (28%) or MAP (40%) than had low complement levels (9%) (P = 0.0001 for each). In probable SLE, MAP scores of >0.8 at enrollment predicted fulfillment of a fourth ACR criterion within 18 months (hazard ratio 3.11, P < 0.01).ConclusionComplement activation occurs in some patients with probable SLE and can be detected with higher frequency by evaluating CB‐CAPs and MAP than by assessing traditional serum complement protein levels. A MAP score above 0.8 predicts transition to classifiable SLE according to ACR criteria.

Randomised prospective trial to assess the clinical utility of multianalyte assay panel with complement activation products for the diagnosis of SLE

ObjectiveWe compared the physician-assessed diagnostic likelihood of SLE resulting from standard diagnosis laboratory testing (SDLT) to that resulting from multianalyte assay panel (MAP) with cell-bound complement activation products (MAP/CB-CAPs), which...

Cell bound complement activation products alone and in combination with low serum complement C3 or C4 have superior diagnostic performance in systemic lupus erythematosus

Abstract BACKGROUND Cell-bound complement activation products (CB-CAPs) are sensitive and specific diagnostic markers of systemic lupus erythematosus (SLE). We compared the performance of CB-CAPs to low serum complement C3 or C4 in distinguishing SLE from other rheumatic diseases and healthy individuals. METHODS Adult subjects (n=1200) were enrolled from multiple academic centers, including SLE (498), healthy individuals (252) and subjects with other rheumatic diseases (450). Erythrocyte bound C4d [EC4d] and B-Lymphocyte bound C4d [BC4d] were quantitated using flow cytometry. Serum C3 and C4 levels were determined using immunoturbidimetry. Measurements included sensitivity, specificity, area under the curve (AUC) of the receiver operating characteristic curve (ROC) and Youden Index, for each marker as well as combinations. RESULTS Abnormal CB-CAPs status yielded 62% sensitivity with 88% specificity in distinguishing SLE from the group with other diseases compared to low C3/C4 status − 38% sensitivity, 93% specificity. Youden index was 0.492±0.03 for CB-CAPs compared to 0.313±0.03 for low C3/C4 (p&amp;lt;0.01). AUC was higher with BC4d (0.72) than with EC4d (0.68; p&amp;lt;0.01), low C3 (0.62; p&amp;lt;0.01), low C4 (0.62; p&amp;lt;0.01) and low C3 and/or C4 levels (0.66; p&amp;lt;0.01). The cumulative complement scoring system yielded higher AUC (0.81). A score with greater than 1 complement abnormality yielded 45% sensitivity and 98% specificity. CONCLUSION Our data suggests that CB-CAPs have greater diagnostic performance than low serum complement C3/C4. The combination of these complement abnormalities in a composite complement score is superior in distinguishing SLE from other rheumatic diseases and healthy individuals.

Cell-bound complement activation products (CB-CAPs) have high sensitivity and specificity in pediatric-onset systemic lupus erythematosus and correlate with disease activity.

Elevated levels of cell-bound complement activation products (CB-CAPs) (C4d deposition on B lymphocytes (BC4d) and/or erythrocytes (EC4d)) are sensitive and specific in diagnosis and monitoring of adult systemic lupus erythematosus (SLE). Our objective was to evaluate the role of CB-CAPs for diagnosis and monitoring of pediatric-onset SLE (pSLE). A prospective cohort study of 28 pSLE and 22 juvenile arthritis patients was conducted. SLE disease activity was determined using a clinical Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) that excluded serologies. Autoantibodies were measured using solid-phase immunoassays, C3 and C4 using immunoturbidimetry, and CB-CAPs using quantitative flow cytometry. Abnormal CB-CAPs were defined as EC4d or BC4d above the 99th percentile for healthy adults (>14 and > 60 net mean fluorescence intensity (MFI), respectively). Performance characteristics of CB-CAPs were assessed using area under the curve (AUC) for receiver operating characteristics. Linear mixed effect models evaluated the correlation between CB-CAPs and clinical SLEDAI over 6 months. BC4d yielded higher AUC (0.91 ± 0.04) than C3 (0.63 ± 0.08) and C4 (0.67 ± 0.08) ( p < 0.05). Abnormal CB-CAPs were 78% sensitive and 86% specific for diagnosis of pSLE (Youden's index = 0.64 ± 0.11). In contrast to BC4d, EC4d levels correlated with clinical SLEDAI ( p < 0.01). CB-CAPs (EC4d and BC4d) have higher sensitivity and specificity than low complement in pSLE, and may help with diagnosis of pSLE. EC4d could provide a useful biomarker for disease activity monitoring.

SLE and Serum Complement: Causative, Concomitant or Coincidental?

Background Systemic Lupus Erythematosus (SLE) is an incurable autoimmune disorder with complement activation playing a key role in the pathogenesis of immune-mediated tissue injury. While quantifying complement to monitor SLE disease activity has been the standard of care since the 1950s, decreased complement levels are not consistently associated with flares. Objective We seek to clarify the SLE phenotype in which complement deficiency is causative, concomitant, or coincidental. Methods A PUBMED literature review was conducted using key words 'complement,' 'SLE,' and 'SLE flares' in English-only journals from 1972-2017. Relevant clinical studies and review articles were found that examined the measurement of complement levels in SLE, and more specifically, interpretation of low serum complement levels regardless of disease activity. Conclusion Complement activation plays a key role in the pathophysiology of SLE and it is recommended to continue monitoring serum levels of C3 and C4 to assess for disease activity. However, it is important to note that decreased serum complement is not consistently associated with disease flares.It is clinically important to find novel ways to assess disease activity in SLE. Reduced serum levels of cell-bound complement activation products may more accurately reflect disease activity than conventional serum C3 and C4 monitoring.

SLE and Serum Complement: Causative, Concomitant or Coincidental?

Background:Systemic Lupus Erythematosus (SLE) is an incurable autoimmune disorder with complement activation playing a key role in the pathogenesis of immune-mediated tissue injury. While quantifying complement to monitor SLE disease activity has been the standard of care since the 1950s, decreased complement levels are not consistently associated with flares.Objective:We seek to clarify the SLE phenotype in which complement deficiency is causative, concomitant, or coincidental.Methods:A PUBMED literature review was conducted using key words 'complement,' 'SLE,’ and ‘SLE flares’ in English-only journals from 1972-2017. Relevant clinical studies and review articles were found that examined the measurement of complement levels in SLE, and more specifically, interpretation of low serum complement levels regardless of disease activity.Conclusion:Complement activation plays a key role in the pathophysiology of SLE and it is recommended to continue monitoring serum levels of C3 and C4 to assess for disease activity. However, it is important to note that decreased serum complement is not consistently associated with disease flares.It is clinically important to find novel ways to assess disease activity in SLE. Increased serum levels of cell-bound complement activation products may more accurately reflect disease activity than conventional serum C3 and C4 monitoring.

Validation of a multi-analyte panel with cell-bound complement activation products for systemic lupus erythematosus

BackgroundWe describe the analytical validation of an assay panel intended to assist clinicians with the diagnosis of systemic lupus erythematosus (SLE). The multi-analyte panel includes quantitative assessment of complement activation and measurement of autoantibodies. MethodsThe levels of the complement split product C4d bound to erythrocytes (EC4d) and B-lymphocytes (BC4d) (expressed as mean fluorescence intensity [MFI]) are measured by quantitative flow cytometry, while autoantibodies (inclusive of antinuclear and anti-double stranded DNA antibodies) are determined by immunoassays. Results of the multi-analyte panel are reported as positive or negative based on a 2-tiered index score. Post-phlebotomy stability of EC4d and BC4d in EDTA-anticoagulated blood is determined using specimens collected from patients with SLE and normal donors. Three-level C4 coated positive beads are run daily as controls. Analytical validity is reported using intra-day and inter-day coefficient of variation (CV). ResultsEC4d and BC4d are stable for 2days at ambient temperature and for 4days at 4°C post-phlebotomy. Median intra-day and inter-day CV range from 2.9% to 7.8% (n=30) and 7.3% to 12.4% (n=66), respectively. The 2-tiered index score is reproducible over 4 consecutive daysupon storage of blood at 4°C. A total of 2,888 three-level quality control data were collected from 6 flow cytometers with an overall failure rate below 3%. Median EC4d level is 6 net MFI (Interquartile [IQ] range 4-9 net MFI) and median BC4d is 18 net MFI (IQ range 13-27 net MFI) among 86,852 specimens submitted for testing. The incidence of 2-tiered positive test results is 13.4%. ConclusionWe have established the analytical validity of a multi-analyte assay panel for SLE.

The Avise Lupus Test and Cell-bound Complement Activation Products Aid the Diagnosis of Systemic Lupus Erythematosus.

Background:Systemic lupus erythematosus (SLE) is a multifaceted disease, and its diagnosis may be challenging. A blood test for the diagnosis of SLE, the Avise Lupus test, has been recently commercialized and validated in clinical studies.Objectives:To evaluate the use of the Avise Lupus test by community rheumatologists.Methods:The study is a longitudinal, case-control, retrospective review of medical charts. Cases had a positive test result, and controls had a negative result; all patients were anti-nuclear antibodies (ANA) positive but negative for SLE-specific autoantibodies. Features of SLE, diagnosis, and medications at two time points were recorded.Results:Twenty of the 23 cases (87%) and 4 of the 23 controls (17%) were diagnosed with SLE (sensitivity=83%; specificity=86%). More cases than controls (43% vs. 17%) fulfilled 4 American College of Rheumatology (ACR) classification criteria of SLE. Sensitivity of the test was significantly higher than the ACR score (83% vs. 42%, p=0.006). A higher percentage of patients who met the classification criteria had elevated cell-bound complement activation products (CB-CAPs) compared to patients who did not. Anti-rheumatic medications were used in a higher percentage of cases than controls (83% vs. 35% at baseline, p=0.002), suggesting that cases were treated more aggressively early on.Conclusion:A positive Avise Lupus test result aids in formulating a SLE diagnosis when diagnosis based on standard-of-care tests and clinical features may be challenging, and impacts patient management. Prospective studies will be performed to better evaluate the clinical utility of the test and of CB-CAPs as biomarkers of SLE.

Reduction in erythrocyte-bound complement activation products and titres of anti-C1q antibodies associate with clinical improvement in systemic lupus erythematosus

BackgroundThe relationship between cell-bound complement activation products (CB-CAPs: EC4d, EC3d), anti-C1q, soluble complement C3/C4 and disease activity in systemic lupus erythematosus (SLE) was evaluated.MethodsPer protocol, at baseline all SLE subjects...

Probable systemic lupus erythematosus with cell-bound complement activation products (CB-CAPS)

Complement activation is a key feature of systemic lupus erythematosus (SLE). Detection of cell-bound complement activation products (CB-CAPS) occurs more frequently than serum hypocomplementemia in definite lupus. We describe a patient with normocomplementemic probable SLE who did not fulfill ACR classification criteria for lupus, but the diagnosis was supported by the presence of CB-CAPS.

Systemic lupus erythematosus and primary fibromyalgia can be distinguished by testing for cell-bound complement activation products

ObjectiveWe sought to establish the performance of cell-bound complement activation products (CB-CAPs) as a diagnostic tool to distinguish primary fibromyalgia (FM) from systemic lupus erythematosus (SLE).MethodsA total of 75 SLE...

Biomarkers for childhood-onset systemic lupus erythematosus.

Childhood-onset systemic lupus erythematosus (cSLE) is a systemic autoimmune disease characterized by the presence of autoantibodies. cSLE often affects multiple organs in the body and is known to have a poorer prognosis than adult-onset disease (Azevedo et al. 2014). Current laboratory tests are clearly insufficient for identifying and monitoring the disease. Recent studies have yielded novel biomarkers for cSLE which can be used for monitoring disease activity and response to treatment. The most encouraging biomarkers will be discussed herein and include cell-bound complement activation products, some genomic profiles, and urinary proteins such as neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and others. Previous studies suggested that a combination of the novel biomarkers might help to enhance sensitivity and specificity for early diagnosis, disease monitoring, and prediction of cSLE flares.

Cell-bound complement activation products in systemic lupus erythematosus: comparison with anti-double-stranded DNA and standard complement measurements

ObjectiveTo compare the performance characteristics of cell-bound complement (C4d) activation products (CBCAPS) on erythrocyte (EC4d) and B cells (BC4d) with antibodies to double-stranded DNA (anti-dsDNA) and complement C3 and C4...

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.