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

Altered Th17/Treg Ratio in Peripheral Blood of Systemic Lupus Erythematosus but Not Primary Antiphospholipid Syndrome

Introduction: The role of the immune response in the pathogenesis of antiphospholipid syndrome (APS) remains elusive. It is possible that differences in the frequencies of Th17 cells and/or defects in the immunoregulatory mechanisms are involved in the pathogenesis of APS. Our aim was to determine the peripheral blood Th cells phenotype and the circulating cytokine profile in patients with primary APS (pAPS) and compare it with systemic lupus erythemathosus (SLE) as disease control group.

Methods: The frequencies of circulating regulatory T cells (Tregs) were determined in PBMCs from 36 patients with pAPS by flow cytometry. As control groups we included 21 age- and gender-matched healthy controls (HC) and 11 patients with SLE. The suppressive capacity of Tregs was evaluated in vitro by coculture assay. On the other hand, intracellular cytokine production was assessed in Th1, Th2, and Th17 cells and circulating IL-6, IL-10, and IL-35 were measured by Cytometric Bead Array and ELISA. The quantification of Th master gene expression levels was performed by real time quantitative PCR.

Results: pAPS patients and SLE patients did not show differences in the percentage or number of Tregs compared to HC. The suppressive capacity of Tregs was also similar in the three study group. Instead, we found higher FoxP3·mRNA expression levels in pAPS patients and HC than SLE patients. Regarding the Th17 response, patients with pAPS and HC showed a significantly lower frequency of circulating Th17 cells than SLE. However, no differences were observed in the Th1 response between patients and controls. Thus, increased Th17/Th1 and Th17/Treg ratios were found in SLE patients but not in pAPS patients. pAPS and SLE patients had higher serum IL-6 levels than HC but there was not difference between both disease groups. Besides, a significant increase in the immunosuppressive cytokine levels was observed only in pAPS as compared to HC.

Conclusions: Our data demonstrate an increased inflammatory profile of peripheral blood CD4⁺ T cells from SLE as compared with pAPS mostly due to an increased Th17 response. In conclusion, there seems not to be a direct pathogenic role for Th cells in pAPS but in SLE.

Peripheral B-Cell Subset Distribution in Primary Antiphospholipid Syndrome

Background: B-cell differentiation and B-cell tolerance checkpoints may be different in antiphospholipid syndrome (APS) from systemic lupus erythematosus (SLE) and can help to understand differences between them. Our aim was to define alterations of B-cell subsets in patients with primary APS (pAPS) and to compare them with SLE patients and healthy controls (HC). Methods: Cross-sectional study including three study groups: 37 patients with pAPS, 11 SLE patients, and 21 age- and gender-matched HC. We determined the frequencies of different B-cell subsets in peripheral blood naïve and memory compartments. In addition, we measured serum B cell-activating factor (BAFF) levels and circulating pro-inflammatory cytokines, such as IL-6, by commercial ELISA and CBA, respectively. Results: Patients with pAPS showed a lower percentage of immature and naïve B cells than patients with SLE (p = 0.013 and p = 0.010, respectively) and a higher percentage of non-switched memory B cells than patients with SLE (p = 0.001). No differences either in the percentage of switched memory cells or plasma cells were found among the different groups. Serum BAFF levels were higher in SLE patients than in healthy controls and pAPS patients (p = 0.001 and p = 0.017, respectively). A significant increase in the serum BAFF levels was also observed in pAPS patients compared to HC (p = 0.047). Circulating IL-6 levels were higher in SLE and pAPS patients than HC (p = 0.036 and p = 0.048, respectively). A positive correlation was found between serum BAFF and IL-6 levels in patients with SLE but not in pAPS (p = 0.011). Conclusions: Our characterization of peripheral blood B-cell phenotypes in pAPS demonstrates different frequencies of circulating B cells at different stages of differentiation. These differences in the naïve B-cell repertoire could explain the higher number and variety of autoantibodies in SLE patients in comparison to pAPS patients, especially in those with obstetric complications.

Clinical presentation and monitoring of lupus nephritis

The diversity of clinical presentations of lupus nephritis parallel the diversity of pathologic lesions seen in the kidneys of patients with SLE. Renal manifestations range from asymptomatic hematuria or proteinuria to overt nephritic and nephrotic syndromes, rapidly progressive glomerulonephritis, and chronic renal failure. Subclinical nephropathy both during presentation and during monitoring of disease activity is frequently missed because of the notorious unreliability of routine screening urinalyses performed in high-throughput clinical pathology laboratories. Requisitions for urine microscopy should be flagged for special attention in patients at risk for lupus nephritis. Depression of classic complement pathway components and high titers of anti-DNA, anti-nucleosome, or anti-C1q antibodies identify patients are increased risk of renal involvement or flares of nephritis. Several disease activity and damage indexes are available, but they are mostly used in clinical research setting and none has achieved wide use for standard clinical practice.

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.

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.

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.

Cytokines and their receptors as biomarkers of systemic lupus erythematosus

Systemic lupus erythematosus is the most clinically diverse autoimmune disease. Owing to its heterogeneous presentation, clinical management of systemic lupus erythematosus remains as one of the greatest challenges. Therefore, there is a great need to assess disease activity accurately. Biomarkers can be objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes or pharmacologic responses to a therapeutic intervention, and may also predict the risk of the disease, confirm diagnosis, monitor disease activity and provide prognostic information. Cytokines play an important and diverse role in the immune dysregulation in systemic lupus erythematosus. Measuring serum levels of soluble IL-2 receptor, IL-6, IL-10, soluble TNF receptor and IFN-alpha/IFN-induced genes may be promising biomarkers of disease activity in systemic lupus erythematosus.

Peritubular capillary C4d deposition in lupus nephritis different from antibody-mediated renal rejection

C4d deposition in peritubular capillaries (PTC) has been used as a marker of antibody-mediated rejection (AMR). However, PTC C4d deposition is not described in patients with lupus nephritis (LN). C4d deposition in PTC was detected in 455 patients with biopsy proven LN in the present study. Renal tissues from 21 cases of acute AMR served as controls. C4d deposition in PTC was found in 31 patients (6.81%) with LN. Patients with PTC C4d positive showed higher SLEDAI score and higher frequency of hypocomplementemia as compared to C4d negative. The prevalence of ANA, anti-dsDNA, anti-Sm and ACA were higher in C4d positive group, and most of these patients showed the diffuse proliferative glomerular lesion. In contrast with acute AMR, the staining pattern of C4d was granular deposition and the detection of C4d along PTC was accompanied by deposition of IgG and C1q or C3. Electron dense deposition on PTC was observed in most of LN patients. In conclusion, C4d deposition in PTC could be found in a small part of patients with LN. Our study suggested for the first time that C4d positive deposition were close relation with the higher disease activity of LN, and that immune complex formation might be involved in PTC C4d deposition in LN patients, Such PTC C4d deposition is distinct from that of AMR.

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.