Measurement of erythrocyte C4d and complement receptor 1 in systemic lupus erythematosus

Immune complex signatures of patients with active and inactive SLE revealed by multiplex protein binding analysis on antigen microarrays

Systemic lupus erythematosus is characterized by dysfunctional clearance of apoptotic debris and the development of pathogenic autoantibodies. While the complement system is also involved in the disease no attempt has been made to generate a comprehensive view of immune complex formation from various autoantigens. We increased the complexity of autoantibody profiles by measuring the binding of two complement proteins, C3 and C4, in addition to two antibody classes, IgG and IgM, to a collection of autoantigens. These complement components covalently bind to those microarray features where antibodies and other serum components induce complement activation. Using this technology, we compared functional serum antibody profiles of control subjects (n = 31) and patients with lupus erythematosus (n = 61) in the active (n = 22) and inactive (n = 39) phase of the disease. Multivariate analysis was applied to identify contributions of binding data on 25 antigens to the discrimination of the study groups. Receiver operating characteristic analysis was used to portray the discriminative property of each measured parameter for each antigen in pairwise group comparisons. Complement C3 and C4 deposition increased on autoantibody targets in spite of the decreased serum complement concentrations, and decreased on other autoantigens, demonstrating the imbalance of complement function in patients with lupus erythematosus. Our observations confirmed previously known markers of disease and showed that C3 and C4 deposition data were at least as powerful as Ig binding data in separating the study groups.

Comparison of C4d detection on erythrocytes and PTC-C4d to histological signs of antibody-mediated rejection in kidney transplantation

C4d on erythrocytes (EC4d), C4d peritubular capillary deposition (PTC-C4d) staining and histology were compared in a cross-sectional cohort of 146 renal allograft biopsies (132 patients). EC4d levels paralleled PTC-C4d staining, but were more predictive of peritubular capillaritis (PTC). Donor-specific antibodies (DSA), PTC-C4d, EC4d and PTC were analyzed in an independent longitudinal follow-up cohort (96 biopsies, 76 patients). Seventy-six samples were PTC and EC4d concordant, 11 positive and 65 negative, 7 PTC-EC4d+ and 13 PTC+EC4d-. EC4d levels were related to DSA occurrence. With ABMR defined by PTC and DSA, all apparently discordant patients, EC4d negative, were correctly reassigned comparing EC4d level curves with rejection kinetics, with positive EC4d samples predating biopsy or late biopsies compared with ABMR flare-ups. All EC4d-positive patients without PTC or DSA had permanent high EC4d levels unrelated to rejection. EC4d was more abundant in PTC-positive (mean = 108.5%± 3.4; n = 50) than PTC-negative samples (mean = 88.1%± 1.3; n= 96; p < 0.0001). Sensitivity, specificity, positive predictive value and negative predictive value of PTC-C4d and EC4d for PTC were, respectively, 75%, 79%; 64%, 76% (p < 0.05); 28%, 46% (p < 0.05) and 93%, 94%. Values were similar for DSA. A noninvasive blood test, EC4d, and particularly longitudinally monitoring EC4d levels, may increase surrogate ABMR testing options.

Biomarkers for systemic lupus erythematosus

The urgent need for lupus biomarkers was demonstrated in September 2011 during a Workshop sponsored by the Food and Drug Administration: Potential Biomarkers Predictive of Disease Flare. After 2 days of discussion and more than 2 dozen presentations from thought leaders in both industry and academia, it became apparent that highly sought biomarkers to predict lupus flare have not yet been identified. Even short of the elusive biomarker of flare, few biomarkers for systemic lupus erythematosus (SLE) diagnosis, monitoring, and stratification have been validated and employed for making clinical decisions. This lack of reliable, specific biomarkers for SLE hampers proper clinical management of patients with SLE and impedes development of new lupus therapeutics. As such, the intensity of investigation to identify lupus biomarkers is climbing a steep trajectory, lending cautious optimism that a validated panel of biomarkers for lupus diagnosis, monitoring, stratification, and prediction of flare may soon be in hand.

Validation of new biomarkers in systemic autoimmune diseases

Biomarkers have an important influence on the clinical decision-making processes involved in diagnosis, assessment of disease activity, allocation of treatment, and determining prognosis. The clinical usefulness of a biomarker is dependant on demonstration of its validity. Ideally, biomarkers should provide information not available from currently available tests and should be tested as they would be used in clinical practice; however, potential biomarkers could be affected by many different clinical or patient variables-such as disease activity, therapeutic intervention, or the presence of comorbidities--and validation studies might not include all the design features that are required to ensure that the biomarker is a true measure of the clinical process it is intended to reflect. In this Review, we appraise studies that have been conducted to validate six promising new biomarkers for diagnosis, disease activity assessment, or prognosis in patients with systemic autoimmune diseases. We discuss the validity of these six biomarkers with particular reference to the features of the studies that lend weight to or distract from their findings. The intent of this discussion is to draw attention to elements of validation study design that should be considered when evaluating the robustness of a biomarker, which differ according to the marker's intended use.

Prospective assessment of C4d deposits on circulating cells and renal tissues in lupus nephritis: a pilot study

Complement activation plays a key role in the pathogenesis of lupus nephritis (LN), a severe complication of systemic lupus erythematosus (SLE). We prospectively evaluated 15 LN subjects and two control groups: 13 non-SLE renal subjects (control A) and 239 SLE subjects without LN (control B). All had C4d levels on circulating erythrocytes (E-C4d), reticulocytes (R-C4d) and platelets (P-C4d) measured by flow cytometry, while C4d deposition in renal tissue was semiquantitatively assessed in LN subjects and control A using immunoperoxidase staining. Compared with control A, LN biopsies had higher glomerular-C4d scores (p = 0.003), which were associated with more frequent granular glomerular immunofluorescence staining and electron dense deposits (p < 0.001). Compared with control A and B groups, LN subjects had higher E-C4d (p = 0.002 and p = 0.005) and R-C4d levels (p = 0.002 and p = 0.008), respectively. LN subjects were more likely to have P-C4d compared with control A (p = 0.016). In LN, only E-C4d correlated with National Institutes of Health (NIH) activity index (r = 0.55, p = 0.04). In conclusion, LN biopsies showed frequent glomerular-C4d staining associated with immune complex deposits. LN subjects had higher E-C4d and R-C4d levels compared with both control groups. E-C4d levels also correlated with NIH activity index. These findings suggest a potential role of C4d on circulating cells as a biomarker for lupus nephritis.

Systemic lupus erythematosus serum deposits C4d on red blood cells, decreases red blood cell membrane deformability, and promotes nitric oxide production

OBJECTIVE

Systemic lupus erythematosus (SLE) is characterized by intravascular activation of the complement system and deposition of complement fragments (C3 and C4) on plasma membranes of circulating cells, including red blood cells (RBCs). The aim of this study was to address whether this process affects the biophysical properties of RBCs.

METHODS

Serum and RBCs were isolated from patients with SLE and healthy controls. RBCs from healthy universal donors (type O, Rh negative) were incubated with SLE or control serum. We used flow cytometry to assess complement fragment deposition on RBCs. RBC membrane deformability was measured using 2-dimensional microchannel arrays. Protein phosphorylation levels were quantified by Western blotting.

RESULTS

Incubation of healthy universal donor RBCs with sera from patients with SLE, but not with control sera, led to deposition of C4d fragments on the RBCs. Complement-decorated RBCs exhibited significant decreases in both membrane deformability and flickering. Sera from SLE patients triggered a transitory Ca(++) influx in RBCs that was associated with decreased phosphorylation of β-spectrin and with increased phosphorylation of band 3, two key proteins of RBC cytoskeleton. Finally, incubation with SLE sera led to the production of nitric oxide by RBCs, whereas this did not occur with control sera.

CONCLUSION

Our data suggest that complement activation in patients with SLE leads to calcium-dependent cytosketeletal changes in RBCs that render them less deformable, probably impairing their flow through capillaries. This phenomenon may negatively affect the delivery of oxygen to the tissues.

Increased erythrocyte C4D is associated with known alloantibody and autoantibody markers of antibody-mediated rejection in human lung transplant recipients

BACKGROUND

Immune responses to mismatched donor human leukocyte antigens (HLA) are important in the pathogenesis of chronic rejection. This study evaluated whether erythrocyte-bound C4d (E-C4d) is associated with known alloimmune and autoimmune markers of antibody-mediated rejection after human lung transplantation (LTx).

METHODS

Flow cytometry was used to analyze 22 LTx recipients and 15 healthy individuals for E-C4d. Development of antibodies to donor-mismatched HLA (donor-specific antibody [DSA]) and antibodies to HLA were determined using the solid-phase method by Luminex. Development of antibodies to self-antigens, K-alpha-1-tubulin (KA1T) and collagen V (Col-V), were measured by enzyme-linked immunosorbent assay. C3d deposition in lung biopsy specimens was determined by immunohistochemical staining.

RESULTS

Percent E-C4d (%E-C4d) levels were 19.9% in LTx patients vs 3.7% in healthy individuals (p = 0.02). DSA+ patients had higher E-C4d levels than DSA- patients (34.1% vs 16.7%, p = 0.02). In 5 patients with preformed anti-HLA, E-C4d levels were not significantly different vs 13 patients without detectable anti-HLA (p = 0.1). E-C4d levels were higher in patients who developed antibodies to KA1T (p = 0.02) and Col-V (p = 0.03). Recipients with C3d-positive tissue deposition had higher E-C4d levels than patients with C3d-negative biopsy results (p = 0.01).

CONCLUSIONS

Increased %E-C4d levels are found in patients with positive DSA, high antibody titers to KA1T and Col-V, and have C3d+ lung biopsy findings. Therefore, %E-C4d can serve as a potential marker for antibody-mediated rejection after LTx.

Review article: systemic lupus erythematosus: a review for anesthesiologists

Systemic lupus erythematosus (SLE) is a chronic autoimmune connective tissue disorder, with a heterogeneous presentation. Disease severity is wide ranging, with most suffering milder forms; however, it is potentially fatal depending on organ involvement. The disorder was recognized as early as the Middle Ages, with the 12th-century physician Rogerius being the first to apply the term lupus to the classic malar rash, and in 1872, Moric Kaposi first recognized the systemic nature of the disease. Perioperatively, SLE can present major challenges to the anesthesiologist because of accrued organ damage, coagulation defects, and complex management regimes. In this article I highlight adult SLE manifestations and treatments pertinent to the anesthesiologist and discuss perioperative management of these complex patients.

Biomarkers in lupus nephritis

Biomarkers have the potential to be useful tools for noninvasively evaluating and managing patients with lupus nephritis. Many candidate biomarkers have been identified, but they require validation in larger cohorts. It is likely that combinations or biomarker profiles, rather than individual markers, will emerge to help better predict the severity of inflammation, the extent of fibrosis, degree of drug responsiveness, and other variables. This approach has the potential to reduce the use of the renal biopsy, improve therapeutic efficacy, and limit toxicity. We predict algorithms based on genotype and biomarkers combined with clinical presentation will emerge to help guide physicians in management. Assays that show the most potential include serum erythrocyte bound complement C4d, interleukin 17, interleukin 23, interferon score/chemokine score ratio, and anti-C1q antibodies. Such urinary biomarkers as fractional excretion of endothelial-1, monocyte chemoattractant protein-1, vascular cell adhesion molecule-1, and TWEAK (tumor necrosis factor-like weak inducer of apoptosis) may also be useful but require validations.

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.

Erythrocyte C3d and C4d for monitoring disease activity in systemic lupus erythematosus

OBJECTIVE

Disease activity in systemic lupus erythematosus (SLE) is typically monitored by measuring serum C3 and C4. However, these proteins have limited utility as lupus biomarkers, because they are substrates rather than products of complement activation. The aim of this study was to evaluate the utility of measuring the erythrocyte-bound complement activation products, erythrocyte-bound C3d (E-C3d) and E-C4d, compared with that of serum C3 and C4 for monitoring disease activity in patients with SLE.

METHODS

The levels of E-C3d and E-C4d were measured by flow cytometry in 157 patients with SLE, 290 patients with other diseases, and 256 healthy individuals. The patients with SLE were followed up longitudinally. Disease activity was measured at each visit, using the validated Systemic Lupus Activity Measure (SLAM) and the Safety of Estrogens in Lupus Erythematosus: National Assessment (SELENA) version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI).

RESULTS

At baseline, patients with SLE had higher median levels of E-C3d and E-C4d (P < 0.0001) in addition to higher within-patient and between-patient variability in both E-C3d and E-C4d when compared with the 2 non-SLE groups. In a longitudinal analysis of patients with SLE, E-C3d, E-C4d, serum C3, and anti-double-stranded DNA (anti-dsDNA) antibodies were each significantly associated with the SLAM and SELENA-SLEDAI. In a multivariable analysis, E-C4d remained significantly associated with these SLE activity measures after adjusting for serum C3, C4, and anti-dsDNA antibodies; however, E-C3d was associated with the SLAM but not with the SELENA-SLEDAI.

CONCLUSION

Determining the levels of the erythrocyte-bound complement activation products, especially E-C4d, is an informative measure of SLE disease activity as compared with assessing serum C4 levels and should be considered for monitoring disease activity in patients with SLE.

Urine proteome scans uncover total urinary protease, prostaglandin D synthase, serum amyloid P, and superoxide dismutase as potential markers of lupus nephritis

To identify potential biomarkers in immune-mediated nephritis, urine from mice subjected to an augmented passive model of anti-glomerular basement membrane (GBM)-induced experimental nephritis was resolved using two-dimensional gels. The urinary proteome in these diseased mice was comprised of at least 71 different proteins. Using orthogonal assays, several of these molecules, including serum amyloid P (SAP), PG D synthase, superoxide dismutase, renin, and total protease were validated to be elevated in the urine and kidneys of mice during anti-GBM disease, as well as in mice with spontaneously arising lupus nephritis. Among these, urinary protease was the only marker that appeared to be exclusively renal in origin, whereas the others were partly serum-derived. Longitudinal studies in murine lupus demonstrated that total urinary protease had better predictive value for histologically active nephritis (r = 0.78) compared with proteinuria (r = -0.04), azotemia (r = 0.28), or the other markers examined, whereas urine SAP emerged as the single most predictive marker of histological glomerulonephritis. Collectively, these studies uncover total urinary protease, PG D synthase, SAP, and superoxide dismutase as novel biomarkers of anti-GBM disease and lupus nephritis, with stronger correlation to renal disease compared with currently employed biomarkers. These findings could have important diagnostic and prognostic ramifications in the management of these renal diatheses.

The search for lupus biomarkers

Few biomarkers for systemic lupus erythematosus (SLE) have been validated and employed for making clinical decisions. The lack of reliable, specific biomarkers for SLE hampers the proper clinical management of patients with SLE and impedes the development of new lupus therapeutics. This void has led to renewed enthusiasm for identifying biomarkers that precisely and specifically reflect the pathophysiological and clinical changes of SLE. Several laboratory markers have shown early promise as biomarkers for lupus susceptibility, diagnosis and monitoring. These include polymorphisms and copy-number variations of complement C4 and Fcgamma receptor genes (disease susceptibility), cell-bound complement C4d (diagnosis and/or disease activity), CD27(high) plasma cells (disease activity), 'interferon signature' (disease activity) and anti-C1q and anti-NMDA (disease activity and organ involvement). Although these and other promising candidate biomarkers have been identified, they still need to be validated through rigorous, large-scale multicentre studies. This article briefly reviews the historical aspects of lupus biomarkers and summarises current efforts to advance the field.

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.

Molecular basis of complete complement C4 deficiency in two North-African families with systemic lupus erythematosus

Complete deficiency of complement C4 is among the strongest genetic risk factors for human systemic lupus erythematosus (SLE). C4 is a constituent of the RP-C4-CYP21-TNX (RCCX) module in the human leukocyte antigen (HLA) that exhibits inter-individual copy-number and gene-size variations. Here, we studied two North-African families with complete C4 deficiency and SLE. The first included a Moroccan male SLE patient (1P) and a sibling, who were both homozygous for HLA-A*02 B*17 DRB1*07. The second had an Algerian female SLE patient (2P) homozygous for HLA-A*01 B*17 DRB1*13. Early SLE disease onset, the presence of photosensitive rashes, anti-Ro/SSA, renal disease and high titers of antinuclear antibodies were the common features of complete C4 deficiency. Southern blot analyses showed that 1P had monomodular RCCX with a long C4A, whereas 2P had bimodular RCCX with one long C4A and one short C4B. Genomic DNA fragments for these mutant genes were amplified and sequenced. A C>T transition that created the R540X nonsense mutation in C4A was found in 1P. An identical 4-bp insertion that generated the Y1537X nonsense mutation was discovered in both C4A and C4B of 2P. The high concordance of SLE and C4 deficiency among patients with non-DR3 and non-DR2 haplotypes underscores the importance of C4 proteins in the protection against SLE.

T cells and in situ cryoglobulin deposition in the pathogenesis of lupus nephritis

We discuss a 53-year-old woman with systemic lupus erythematosus who presented with vasculitis, hypocomplementemia and nephritis. Although her serum complement 4 (C4) levels were zero, she had four copies of C4 gene. Renal biopsy revealed membranoproliferative glomerulonephritis and the presence of cryoglobulins, detected by electron microscopy, and significant numbers of T cells in the interstitium. Cryoglobulins were considered responsible for the complete consumption of C4 in the serum the levels of which improved gradually after treatment. T cells in the kidney were found to express CD44 and phosphorylated ezrin/radixin/moiesin which explain why they homed to the kidney inappropriately. The contribution of cryoglobulins and T cells in the expression of kidney pathology is discussed.

Human complement components C4A and C4B genetic diversities: complex genotypes and phenotypes

This unit describes methods that can accurately determine the genotypes and phenotypes of human complement components C4A and C4B. Specifically, they allow investigators to determine how many C4 genes are present in a diploid genome of a human subject and to quantify how many of them encode C4A proteins and how many of them encode C4B proteins. In addition, methods to determine how many long and short C4 genes are present in a diploid genome of a subject are described together with experimental strategies to determine haplotypes and order or configuration of these genes in the MHC. Finally, methods to assess the degree of polymorphism in C4A and C4B proteins and whether low protein levels of plasma C4 may be caused by low C4 gene dosages and/or by mutant C4 genes.

Lymphocytotoxic antibodies in systemic lupus erythematosus are associated with disease activity irrespective of the presence of neuropsychiatric manifestations

OBJECTIVES

To evaluate the association of the presence of lymphocytotoxic, anti-beta2-glycoprotein I (anti-beta2-GPI) and anti-ribosomal P (anti-P) antibodies in patients with systemic lupus erythematosus (SLE), presenting or not neuropsychiatric (NP) manifestations, stratified according to the activity of the disease.

METHODS

A total of 138 patients with SLE (59 with active NPSLE, 49 with active non-NPSLE, and 30 with inactive disease) and 57 healthy controls were studied. Disease activity was assessed by the SLE Disease Activity Index (SLEDAI). The presence of lymphocytotoxic antibodies was assessed using a complement-dependent lymphocytotoxicity assay. The presence of anti-beta2-GPI and anti-P antibodies was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Lymphocytotoxic antibodies were detected primarily in patients with active disease, that is in 35 out of 59 (59.3%) NPSLE and 23 out of 49 (46.9%) non-NPSLE patients, whereas only four out of 30 (13.3%) inactive SLE patients and none of the healthy controls exhibited the autoantibody. The frequency of lymphocytotoxic antibodies in active SLE patients, considered as a whole or stratified into NPSLE or non-NPSLE, was significantly increased in relation to inactive SLE patients (p<0.001 for each comparison). No significant difference was observed when comparing active NPSLE with non-NPSLE patients. No associations were observed between the presence of anti-beta2-GPI or anti-P antibodies and the activity of SLE or the presence of lymphocytotoxic antibodies.

CONCLUSIONS

Lymphocytotoxic antibodies occurred more frequently in patients with active SLE than in patients with inactive disease, irrespective of the presence of NP manifestations, a finding that is similar to classical biomarkers of lupus activity (anti-dsDNA and complement). These results indicate that the assessment of the presence of lymphocytotoxic antibodies may be an additional useful tool for the evaluation of SLE activity.

Antibody CR1-2B11 recognizes a non-polymorphic epitope of human CR1 (CD35)

Measurement of erythrocyte [red blood cells (RBC)] complement receptor type 1 (CR1, CD35) has the potential to serve as a sensitive assessment of complement activation and immune complex clearance. All previously reported monoclonal antibodies (MoAb) to the extracellular region of CR1 recognize epitopes within the long homologous repeats (LHR) of CR1 and the epitopes for the most frequently used MoAbs are repeated at least twice per CR1 molecule. Furthermore, CR1 exhibits structural polymorphism characterized by a variable number of LHR per molecule. Thus, accurate enumeration of cell surface CR1 using currently available MoAb would require that the results be corrected for the number of antibody epitopes per CR1 molecule encoded by each individual's alleles. To obtain a MoAb to a non-polymorphic epitope on human CR1, hybridomas were generated from mice immunized with recombinant soluble CR1 (sCR1) and MoAb were screened for those that recognized the full-length extracellular domain but failed to bind to all four recombinant LHR fragments. A single antibody, CR1-2B11, was identified and was found to recognize an epitope located wholly within SCR29-30 of CR1, NH2-terminal to an elastase cleavage site. Like other CR1 MoAb, the CR1-2B11 epitope expression decreased on old erythrocytes compared to younger cells and CR1-2B11 did not identify a CR1 'stump' on RBC. Importantly, CR1-2B11 immunofluorescence did not change with storage or handling of RBC, unlike the apparent decrease in immunofluorescence observed with other MoAb. CR1-2B11 should be useful for the accurate enumeration of RBC CR1.

Gene copy-number variation and associated polymorphisms of complement component C4 in human systemic lupus erythematosus (SLE): low copy number is a risk factor for and high copy number is a protective factor against SLE susceptibility in European Americans

Interindividual gene copy-number variation (CNV) of complement component C4 and its associated polymorphisms in gene size (long and short) and protein isotypes (C4A and C4B) probably lead to different susceptibilities to autoimmune disease. We investigated the C4 gene CNV in 1,241 European Americans, including patients with systemic lupus erythematosus (SLE), their first-degree relatives, and unrelated healthy subjects, by definitive genotyping and phenotyping techniques. The gene copy number (GCN) varied from 2 to 6 for total C4, from 0 to 5 for C4A, and from 0 to 4 for C4B. Four copies of total C4, two copies of C4A, and two copies of C4B were the most common GCN counts, but each constituted only between one-half and three-quarters of the study populations. Long C4 genes were strongly correlated with C4A (R=0.695; P<.0001). Short C4 genes were correlated with C4B (R=0.437; P<.0001). In comparison with healthy subjects, patients with SLE clearly had the GCN of total C4 and C4A shifting to the lower side. The risk of SLE disease susceptibility significantly increased among subjects with only two copies of total C4 (patients 9.3%; unrelated controls 1.5%; odds ratio [OR] = 6.514; P=.00002) but decreased in those with > or =5 copies of C4 (patients 5.79%; controls 12%; OR=0.466; P=.016). Both zero copies (OR=5.267; P=.001) and one copy (OR=1.613; P=.022) of C4A were risk factors for SLE, whereas > or =3 copies of C4A appeared to be protective (OR=0.574; P=.012). Family-based association tests suggested that a specific haplotype with a single short C4B in tight linkage disequilibrium with the -308A allele of TNFA was more likely to be transmitted to patients with SLE. This work demonstrates how gene CNV and its related polymorphisms are associated with the susceptibility to a human complex disease.

Use of serum or buffer-changed EDTA-plasma in a rapid, inexpensive, and easy-to-perform hemolytic complement assay for differential diagnosis of systemic lupus erythematosus and monitoring of patients with the disease

We previously described a simplified quantitative hemolytic assay for classical pathway (CP) hemolytic function in serum that has been shown to correlate with the 50% hemolytic complement (CH50) assay. In the present study, we used this assay to compare CP functions; plasma levels of C3, C4, and C3dg; and ratios of C3dg to C3 in healthy individuals and patients with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA) with different degrees of complement activation. A significant depression in CP function and levels of C4 and C3 and increased C3dg levels and C3dg/C3 ratios were observed in the SLE patients. In patients with RA, CP function was normal, whereas C3, C4, and C3dg levels and the C3dg/C3 ratio were elevated. The SLE results are compatible with systemic complement consumption, whereas the RA data suggest an acute-phase reaction with a normal C3 catabolic rate. To facilitate the handling of patient samples, we also developed a method to restore the hemolytic function of EDTA-plasma by transferring it to Veronal-buffered saline containing the thrombin inhibitor lepirudin. This process inhibits coagulation and enables complement activation, allowing a longer time lag between sample harvesting and testing. These results, combined with previous correlation studies, suggest that the CP hemolytic assay can effectively replace the CH50 assay for routine SLE differential diagnosis and monitoring of disease activity.

Cell-Bound Complement Activation Products (CB-CAPs) as a Source of Lupus Biomarkers

Measurement of serum C3 and C4 has been used for several decades to monitor disease activity in patients with SLE. Despite the limited utility and recognized weaknesses of these assays, they have remained the gold standard during an era of unprecedented discovery in the complement field. The current urgent need for lupus biomarkers warrants efforts to mine the complement system for assays superior to serum C3 and C4. Recent studies of soluble and cell-bound complement activation products hold promise for achieving this goal.

Rapid flow cytometric measurement of cytokine-induced phosphorylation pathways [CIPP] in human peripheral blood leukocytes

Current strategies designed to assess cells in the peripheral blood are limited to evaluation of phenotype or delayed measurement [>6 h] of function, usually quantifying cytokine production, cytolytic activity, or response to antigens. We reasoned that measurable abnormalities in signaling pathways could reflect pathological environs that cells experience in the setting of inflammatory states/cancer and could be represented in the peripheral blood. Two major pathways regulating the immune response are the JAK/STAT and MAPK/ERK pathways. These pathways are initiated by ligand-receptor binding and are rapidly propagated by subsequent protein phosphorylation cascades. We evaluated the brief application of cytokines in vitro to interrogate the early phosphorylation events of these signaling pathways in normal peripheral blood mononuclear cells (PBMC). Individual cytokine doses and time intervals of treatment were assessed to identify conditions useful in a clinical laboratory and as an initial goal to induce maximal phosphorylation. Surprisingly, all of the STAT proteins assessed and ERK1/2 are maximally phosphorylated within 15 min in human PBMC simply following addition of cytokines without preactivation of the cells. At 2 h, cells typically return to their basal phosphorylation states. For most of the cytokines tested, increased phosphorylation directly correlated with increased concentrations of the individual cytokines. These strategies will enable robust development of simple blood analyses to identify normal levels as well as impairments in STAT and MAPK/ERK signaling pathways associated with various human disease states including acute and chronic inflammatory conditions throughout clinical immunology.

Complement receptor 1 and 2 deficiency increases coxsackievirus B3-induced myocarditis, dilated cardiomyopathy, and heart failure by increasing macrophages, IL-1beta, and immune complex deposition in the heart

Complement and complement receptors (CR) play a central role in immune defense by initiating the rapid destruction of invading microorganisms, amplifying the innate and adaptive immune responses, and mediating solubilization and clearance of immune complexes. Defects in the expression of C or CR have been associated with loss of tolerance to self proteins and the development of immune complex-mediated autoimmune diseases such as systemic lupus erythematosus. In this study, we examined the role of CR on coxsackievirus B3 (CVB3)-induced myocarditis using mice deficient in CR1/2. We found that CR1/2 deficiency significantly increased acute CVB3 myocarditis and pericardial fibrosis resulting in early progression to dilated cardiomyopathy and heart failure. The increase in inflammation was not due to increased viral replication, which was not significantly altered in the hearts of CR1/2-deficient mice, but was associated with increased numbers of macrophages, IL-1beta levels, and immune complex deposition in the heart. The complement regulatory protein, CR1-related gene/protein Y (Crry), was increased on cardiac macrophage populations, while immature B220(low) B cells were increased in the spleen of CR1/2-deficient mice during acute CVB3-induced myocarditis. These results show that expression of CR1/2 is not necessary for effective clearance of CVB3 infection, but prevents immune-mediated damage to the heart.

Consumption of erythrocyte CR1 (CD35) is associated with protection against systemic lupus erythematosus renal flare

Erythrocyte complement receptor type one (E-CR1) is thought to protect against immune complex (IC) disease through interactions that lead to E-CR1 consumption, and low E-CR1 levels are characteristic of systemic lupus erythematosus (SLE). The purpose of this study was to test the hypothesis that E-CR1 consumption can predict or mark SLE flare. Recurrently active SLE patients [n = 43; 28 with past or present major renal manifestations (SLER) and 15 without (SLENR)], were evaluated every 2 months by detailed protocol testing (mean follow-up 22 months), including direct measurements of E-CR1 levels using a radioimmunoassay. In all patients, detectable E-CR1 levels fluctuated widely through acute periods of consumption and regeneration, preventing the use of any single value as a baseline. However, when individual chronic baseline values were used, determined as the mean of all E-CR1 values 4 months or more from a flare, a clear trend was observed. In 16 of 16 instances of non-renal flare in SLER patients, E-CR1 levels decreased at flare (mean decrease 34%, P < 0.0001). In contrast, no consistent difference was observed for flare in SLENR patients or for renal flare in SLER patients. Changes in E-CR1 levels did not correlate with plasma CR1 levels. In conclusion, single occurrences of E-CR1 consumption did not generally predict or mark SLE flare. However, compared to the average E-CR1 levels measured during no-flare intervals, E-CR1 consumption in SLER patients at flare was strongly associated with freedom from signs of renal involvement. We postulate that E-CR1 consumption reflects E-CR1 function that includes protecting against SLE nephritis.

Platelet C4d is highly specific for systemic lupus erythematosus

OBJECTIVE

Complement-activation product C4d is deposited on normal erythrocytes, while abnormal levels have been observed on the surface of erythrocytes of patients with systemic lupus erythematosus (SLE). This study examines whether C4d also deposits on human platelet surfaces, and whether platelet-bound C4d may provide a biomarker for SLE.

METHODS

We conducted a cross-sectional study of 105 patients with SLE, 115 patients with other diseases, and 100 healthy controls. Levels of C4d on the surface of platelets were examined by flow cytometry and scanning confocal microscopy. Statistical analyses were performed to determine the clinical variables associated with platelet C4d.

RESULTS

Abnormal levels of platelet C4d were found to be highly specific for SLE. Platelet C4d was detected in 18% of patients with SLE, being 100% specific for a diagnosis of SLE compared with healthy controls and 98% specific for SLE compared with patients with other diseases (P < 0.0001). In addition, platelet C4d was significantly associated with positivity for lupus anticoagulant (P < 0.0001) and anticardiolipin antibodies of the IgG (P = 0.035) or the IgM (P = 0.016) isotype. Platelet C4d was also significantly associated with SLE disease activity according to the SLE Disease Activity Index (P = 0.039), low serum C4 (P = 0.046), an elevated erythrocyte sedimentation rate (P = 0.006), and abnormal levels of C4d on erythrocytes (P < 0.0001).

CONCLUSION

This observation suggests that platelet-bound C4d may be a useful biomarker for SLE and may be a clue to the pathogenic mechanisms responsible for the myriad thrombotic and vascular complications of lupus associated with antiphospholipid antibodies.

The role of biomarkers in the assessment of lupus

Although considered a prototypic autoimmune disease, the hallmark of systemic lupus erythematosus (SLE) is its heterogeneity. Accordingly, manifestations can vary widely from person to person, with the potential involvement of virtually any bodily organ. Furthermore, the genetic abnormalities underlying this condition are complicated, with diverse genetic polymorphisms described in different ethnic groups, strongly suggesting that the actual pathology underlying the immunologic disarray might not be the same for each patient. Evolving concepts of genetics and immunity have clarified that patients can carry unique arrays of exacerbating and protective factors. These factors, in conjunction with variable environmental triggers for SLE, probably determine the sequelae that an individual experiences. Therefore, it is not surprising that the clinical manifestations are diverse, the temporal sequence of organ involvement often unpredictable, and that the flares of inflammatory activity that characterize SLE can either remit without consequence or leave permanent damage in their wake. It is widely accepted that the current standard of care for SLE patients is inadequate. Programs to develop and test new drug and/or device therapies have been ongoing since the mid-1990s but have encountered formidable obstacles. With the current burst of drug discovery and the advent of several large international trials of promising new agents, the challenge to overcome these obstacles has never been greater. A burgeoning literature in the past decades nevertheless suggests that despite the complexities of the many immunologic pathways that impact on SLE, characteristic biologic markers are emerging as potential signposts that can characterize patient subgroups, predict prognosis, mark the exacerbations and remissions of SLE flares, and serve as endpoints in the determination of the dosing and timing of immune-modulating treatments. Several of the promising biomarkers are addressed in this chapter.

Frühdiagnose des systemischen Lupus erythematodes (SLE)

Early diagnosis in patients with systemic lupus erythematosus (SLE) remains a challenge even to experienced rheumatologists. This is due to the diversity of presentation with single or multiple manifestations and the variable course. In contrast to the considerable progress in treatment modalities no reliable diagnostic marker has been developed in the last years. So the diagnosis is made largely on clinical grounds with great awareness of anamnestic features, thoroughly performed physical examination supported by laboratory and organspecific tests. The 1997 revised ACR classification criteria are of great value, though they do not satisfy in every single case. With respect to the potentially life or organ threatening course of SLE a good interdisciplinary cooperation of general practitioners and specialists with rheumatologists is of special importance.

SLE: challenges and candidates in human disease

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immunological hyperactivity and multi-system organ damage. A complex genetic trait involving multiple genes, with both genetic heterogeneity and a threshold effect for disease expression, SLE involves abnormalities of both the innate and adaptive immune systems. Recognition of an 'interferon signature' in SLE leukocytes, of the role of B cells in promoting disease activity, and of FCGR3A alleles as a biomarker of end organ damage, provide important insights into disease pathogenesis. Nonetheless, coordinated studies in humans and model systems hold promise for an even more rapid advance in understanding pathways of disease development and strategies for intervention. More effective markers of disease risk, disease activity, severity of organ damage and outcomes would facilitate earlier diagnosis and guide appropriately targeted treatment.

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.

Complement and its breakdown products in SLE

The complement system has important protective functions in both the innate and the adaptive immune systems but can also, when inappropriately activated, cause tissue damage. Complement deficiency predisposes to infection and also to development of autoimmune disease, especially SLE, and complement is at the same time involved in the pathogenesis of this disease. In this review, various aspects of this dualism are discussed. An overview of activation pathways and activation products is given, together with a description of autoimmunity against complement and the potential of complement regulation in future therapeutics.

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.

Reticulocytes bearing C4d as biomarkers of disease activity for systemic lupus erythematosus

OBJECTIVE

There is an urgent need for biomarkers with which to monitor disease activity in patients with systemic lupus erythematosus (SLE). We recently showed that abnormal levels of C4d, an activation-derived fragment of complement component C4, are deposited on the surface of erythrocytes from patients with SLE. This study focused on reticulocytes, the youngest and shortest-lived erythrocytes (lifespan 24-48 hours), with the objective of testing our hypothesis that when reticulocytes emerge from the bone marrow, they are immediately exposed to and acquire C4d at levels proportionate to the extent of complement activation at that time, thereby reflecting disease activity in SLE.

METHODS

We conducted a cross-sectional study of 156 patients with SLE, 140 patients with other diseases, and 159 healthy controls. Levels of C4d on the surface of reticulocytes were examined using a 2-color flow cytometric assay. The results were analyzed for correlations with SLE disease activity.

RESULTS

A wide range of increased levels of reticulocyte C4d was specifically detected in SLE patients. These levels fluctuated in SLE patients and correlated with clinical disease activity, as determined by the Safety of Estrogens in Lupus Erythematosus: National Assessment (SELENA) version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and the Systemic Lupus Activity Measure (SLAM). Specifically, in cross-sectional analyses, patients with reticulocyte C4d levels in the highest quartile compared with those in the lowest quartile had significantly higher SELENA-SLEDAI (P = 0.00002) and SLAM (P = 0.02) scores. Longitudinal observation demonstrated that the reticulocyte C4d levels changed in relation to the clinical course in individual patients.

CONCLUSION

These findings support our hypothesis that C4d-bearing reticulocytes may serve as biomarkers of disease activity in patients with SLE.