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

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.

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.

Platelet bound complement split product (PC4d) is a marker of platelet activation and arterial vascular events in Systemic Lupus Erythematosus

Platelet-bound complement activation products (PC4d) are associated with thrombosis in Systemic Lupus Erythematosus (SLE). This study investigated the effect of PC4d on platelet function, as a mechanistic link to arterial thrombosis. In a cohort of 150 SLE patients, 13 events had occurred within five years of enrollment. Patients with arterial events had higher PC4d levels (13.6 [4.4-24.0] vs. 4.0 [2.5-8.3] net MFI), with PC4d 10 being the optimal cutoff for event detection. The association of arterial events with PC4d remained significant after adjusting for antiphospholipid status, smoking, and prednisone use (p = 0.045). PC4d levels correlated with lower platelet counts (r = -0.26, p = 0.002), larger platelet volumes (r = 0.22, p = 0.009) and increased platelet aggregation: the adenosine diphosphate (ADP) concentration to achieve 50% maximal aggregation (EC₅₀) was lower in patients with PC4d 10 compared with PC4d < 10 (1.6 vs. 3.7, p = 0.038, respectively). These results suggest that PC4d may be a mechanistic marker for vascular disease in SLE.

Complement testing in the clinical laboratory

The complement system is the human's first line of defense against microbial pathogens because of its important housekeeping and infection/inflammation roles. It is composed of a series of soluble and cell-bound proteins that are activated in a cascade effect, similar to the coagulation pathways. There are different pattern recognizing molecules that activate the complement system in response to stimuli or threats, acting through three initiation pathways: classical, lectin, and alternative. All three activation pathways converge at the C3 component and share the terminal pathway. The main outputs of the complement system action are lytic killing of microbes, the release of pro-inflammatory anaphylatoxins, and opsonization of targets. Laboratory testing is relevant in the setting of suspected complement deficiencies, as well as in the emerging number of diseases related to dysregulation (over-activation) of complement. Most common assays measure complement lytic activity and the different complement component concentrations. Specialized testing includes the evaluation of autoantibodies against complement components, activation fragments, and genetic studies. In this review, we cover laboratory testing for complement and the conditions with complement involvement, as well as current challenges in the field.

Systemic lupus erythematosus: The search for the ideal biomarker

During the last decades, there has been an increased interest in the discovery and validation of biomarkers that reliably reflect specific aspects of lupus. Although many biomarkers have been developed, few of them have been validated and used in clinical practice, but with unsatisfactory performances. Thus, there is still a need to rigorously validate many of these novel promising biomarkers in large-scale longitudinal studies and also identify better biomarkers not only for lupus diagnosis but also for monitoring and predicting upcoming flares and response to treatment. Besides serological biomarkers, urinary and cerebrospinal fluid biomarkers have emerged for assessing both renal and central nervous system involvement in systemic lupus erythematosus, respectively. Also, novel omics techniques help us to understand the molecular basis of the disease and also allow the identification of novel biomarkers which may be potentially useful for guiding new therapeutic targets.

Utility of the AVISE Connective Tissue Disease test in predicting lupus diagnosis and progression

Background

The AVISE Connective Tissue Disease (CTD) test uses autoantibody, erythrocyte-bound C4d (EC4d) and B-cell-bound C4d (BC4d) levels to aid in diagnoses of SLE, other CTDs and fibromyalgia. We evaluated the utility of the AVISE CTD test in predicting SLE disease development and damage progression.

Methods

Patients who had undergone AVISE CTD testing were assessed for SLE diagnosis by the Systemic Lupus International Collaborating Clinics (SLICC) and American College of Rheumatology criteria and for SLE damage by the Systemic Lupus International Collaborating Clinics Damage Index (SDI) at the time of AVISE testing (t=0) and 2 years later (t=2).

Results

Among 117 patients without a previous diagnosis of SLE, 65% of patients who tested positive developed SLE at t=2, compared with 10.3% of patients who tested non-positive (p<0.0001). AVISE-positive patients fulfilled significantly more SLICC diagnostic criteria than AVISE-non-positive patients at both t=0 (3.8±2.1 vs 1.9±1.1, p=0.001) and t=2 (4.5±2.2 vs 2.1±1.2, p<0.0001). AVISE-positive patients also had had significantly higher SDI at t=2 (1.9±1.3 vs 1.03±1.3, p=0.01). BC4d levels correlated with the number of SLICC criteria at t=0 (r=0.33, p<0.0001) and t=2 (r=0.34, p<0.0001), as well as SDI at t=0 (r=0.25, p=0.003) and t=2 (r=0.26, p=0.002).

Conclusions

The AVISE CTD test can aid in SLE evaluation by predicting SLE disease development and future damage progression.

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

Objective

We 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 reports a two-tiered index test result having 80% sensitivity and 86% specificity for SLE.

Methods

Patients (n=145) with a history of positive antinuclear antibody status were evaluated clinically by rheumatologists and randomised to SDLT arm (tests ordered at the discretion of the rheumatologists) or to MAP/CB-CAPs testing arm. The primary endpoint was based on the change in the physician likelihood of SLE on a five-point Likert scale collected before and after testing. Changes in pharmacological treatment based on laboratory results were assessed in both arms. Statistical analysis consisted of Wilcoxon and Fisher’s exact tests.

Results

At enrolment, patients randomised to SDLT (n=73, age=48±2 years, 94% females) and MAP/CB-CAPs testing arms (n=72, 50±2 years, 93% females) presented with similar pretest likelihood of SLE (1.42±0.06 vs 1.46±0.06 points, respectively; p=0.68). Post-test likelihood of SLE resulting from randomisation in the MAP/CB-CAPs testing arm was significantly lower than that resulting from randomisation to SDLT arm on review of test results (−0.44±0.10 points vs −0.19±0.07 points) and at the 12-week follow-up visit (−0.61±0.10 points vs −0.31±0.10 points) (p<0.05). Among patients randomised to the MAP/CB-CAPs testing arm, two-tiered positive test results associated significantly with initiation of prednisone (p=0.034).

Conclusion

Our data suggest that MAP/CB-CAPs testing has clinical utility in facilitating SLE diagnosis and treatment decisions.