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

Complement C4d as a biomarker for systemic lupus erythematosus and lupus nephritis

Background: Increasing studies in the last decade have led to the widespread understanding that C4d, a split product of complement component 4 (C4), is a potential biomarker for systemic lupus erythematosus (SLE) and lupus nephritis (LN).Purpose: The aim of this review is to summarize the highlights of studies investigating the use of C4d as a biomarker for diagnosing and monitoring SLE and LN patients.Data collection: we searched PubMed/Medline and Wanfang databases using the terms "C4d and systemic lupus erythematosus", "C4d and lupus nephritis", and "Complement C4d".Results: The deposition of C4d on circulating blood cells has been shown in several clinical studies to be a potential diagnostic marker that can be used to monitor patients with SLE. In addition, C4d deposits on circulating blood cells may be a helpful diagnostic marker for LN, one of the most severe complications of SLE. Meanwhile, studies utilizing renal biopsy specimens have indicated that C4d deposition in the renal peritubular capillaries of LN patients may predict more severe LN or a worse patient prognosis. Generally, a high plasma C4d level and a high plasma C4d/C4 ratio may also be promising indicators that can be used to monitor patients with SLE and LN.Conclusions: C4d detection may be a novel strategy for further clinical prediction and therapy.

Systemic evaluation of lymphocyte-bound C4d and immunoglobulins for diagnosis and activity monitoring of Systemic Lupus Erythematosus

OBJECTIVE

To investigate the role of lymphocyte-bound C4d (LB-C4d: T-C4d, B-C4d) and immunoglobulins (LB-Igs: T-IgG, T-IgM, B-κ and B-λ) in the diagnosis and monitoring of SLE.

DESIGN & METHODS

The levels of C4d and Igs on peripheral lymphocytes were measured in 172 patients with SLE, 174 patients with other non-SLE inflammatory diseases and 100 healthy individuals. Immunobinding and blocking experiments were performed to characterize Igs from SLE patients to generate LB-C4d/Igs in vitro. Sixty-five patients with SLE were followed up longitudinally. Disease activity was assessed for each SLE patient.

RESULTS

Patients with SLE had the highest median LB-C4d/Igs levels. LB-C4d had a significant but weak positive association with LB-Igs, with correlation coefficients ranging from 0.008 to 0.316. Anti-cardiolipin IgG and anti-β2GP1 IgG, but not C3 and C4, were found to be closely associated with LB-C4d/Igs formation, with correlations as high as 0.337. Compared to anti-dsDNA, LB-C4d performed better in SLE diagnosis, while B-κ and B-λ performed better in disease activity monitoring.

CONCLUSIONS

Both autoantibodies and receptors on lymphocytes contribute to LB-C4d/Igs formation. LB-C4d/Igs could be used as reliable indicators for SLE diagnosis and activity monitoring.

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.

Systemic Lupus Erythematosus: New Diagnostic and Therapeutic Approaches

Systemic lupus erythematosus (SLE) is a devastating autoimmune disease that can result in substantial morbidity and mortality. Diagnosis and treatment of SLE are clinical challenges. Patient presentation and response to therapy are heterogeneous because of the complex immune dysregulation that results in SLE disease pathogenesis. An intricate interplay between genetic risk and skewing of adaptive and innate immune system responses leads to overproduction of type I interferons and other cytokines, complement activation, immune-complex deposition, and ultimately inflammation and tissue damage. Here, we review the classification criteria as well as standard and emerging diagnostic tools available to identify patients with SLE. We then focus on medical management, including novel therapeutics, nonpharmacologic interventions, and comorbidity management.

Anti-RNP antibodies are associated with the interferon gene signature but not decreased complement levels in SLE

OBJECTIVES

The goals of these studies were to elucidate the inter-relationships of specific anti-nuclear antibody (ANA), complement, and the interferon gene signature (IGS) in the pathogenesis of systemic lupus erythematosus (SLE).

METHODS

Data from the Illuminate trials were analysed for antibodies to dsDNA as well as RNA-binding proteins (RBP), levels of C3, C4 and various IGS. Statistical hypothesis testing, linear regression analyses and classification and regression trees analysis were employed to assess relationships between the laboratory features of SLE.

RESULTS

Inter-relationships of ANAs, complement and the IGS differed between patients of African Ancestry (AA) and European Ancestry (EA); anti-RNP and multiple autoantibodies were more common in AA patients and, although both related to the presence of the IGS, relationships between autoantibodies and complement differed. Whereas, anti-dsDNA had an inverse relationship to C3 and C4, levels of anti-RNP were not related to these markers. The IGS was only correlated with anti-dsDNA in EA SLE and complement was more correlated to the IGS in AA SLE. Finally, autoantibodies occurred in the presence and absence of the IGS, whereas the IGS was infrequent in anti-dsDNA/anti-RBP-negative SLE patients.

CONCLUSION

There is a complex relationship between autoantibodies and the IGS, with anti-RNP associated in AA and both anti-dsDNA and RNP associated in EA. Moreover, there was a difference in the relationship between anti-dsDNA, but not anti-RBP, with complement levels. The lack of a relationship of anti-RNP with C3 and C4 suggests that anti-RNP immune complexes (ICs) may drive the IGS without complement fixation, whereas anti-dsDNA ICs involve complement consumption.

Relationship of complement activation pathway to clinical and pathological characteristics and renal outcome in patients with lupus nephritis

BACKGROUND

Involvement of the complement system in the pathogenesis of lupus nephritis (LN) is well accepted, but its exact role remains unclear. The aim of this study was to investigate the relationship of complement activation pathway to clinical and pathological characteristics and renal outcome in patients with LN.

MATERIAL AND METHODS

Patients with LN were divided into two groups: those in whom the complement system was mainly activated through the classical pathway (low serum C3 and C4 levels; CP group); and those in whom the complement system was solely activated through the alternative pathway (low serum C3 with normal C4 levels; AP group). Clinical and pathological data and renal outcomes were compared between the two groups.

RESULTS

A total of 102 LN patients were enrolled in this study, 63 patients (61.8%) in the CP group and 39 patients (38.2%) in the AP group. LN patients in the CP group had significantly higher SLEDAI (p < 0.001), more anti-dsDNA (p = 0.001), higher renal activity index (p < 0.001), and more class IV LN (p = 0.008) than LN patients in the AP group. Mean length of follow-up was 50.6 ± 26.4 months. Renal outcome in the form of progression of kidney disease was significantly poorer in the CP group in the AP group (p = 0.037).

CONCLUSION

Our findings suggest that evaluation of the complement activation pattern may be useful for evaluating disease activity and predicting the prognosis of LN.

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

Objective

To 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.

Methods

Patients 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.

Results

Of 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.

Conclusion

Approximately one‐third of patients with pSLE transitioned within the study period. MAP of greater than 0.8 predicted disease evolution into classifiable SLE.