The complement is a powerful cascade of the innate immunity and also acts as a bridge between innate and acquired immune defence. Complement activation can occur via three distinct pathways, the ...classical, alternative and lectin pathways, each resulting in the common terminal pathway. Complement activation results in the release of a range of biologically active molecules that significantly contribute to immune surveillance and tissue homeostasis. Several soluble and membrane-bound regulatory proteins restrict complement activation in order to prevent complement-mediated autologous damage, consumption and exacerbated inflammation. The crucial role of complement in the host homeostasis is illustrated by association of both complement deficiency and overactivation with severe and life-threatening diseases. Autoantibodies targeting complement components have been described to alter expression and/or function of target protein resulting in a dysregulation of the delicate equilibrium between activation and inhibition of complement. The spectrum of diseases associated with complement autoantibodies depends on which complement protein and activation pathway are targeted, ranging from autoimmune disorders to kidney and vascular diseases. Nevertheless, these autoantibodies have been identified as differential biomarkers for diagnosis or follow-up of disease only in a small number of clinical conditions. For some autoantibodies, a clear relationship with clinical manifestations has been identified, such as anti-C1q, anti-Factor H, anti-C1 Inhibitor antibodies and C3 nephritic factor. For other autoantibodies, the origin and the functional consequences still remain to be elucidated, questioning about the pathophysiological significance of these autoantibodies, such as anti-mannose binding lectin, anti-Factor I, anti-Factor B and anti-C3b antibodies. The detection of autoantibodies targeting complement components is performed in specialized laboratories; however, there is no consensus on detection methods and standardization of the assays is a real challenge. This review summarizes the current panorama of autoantibodies targeting complement recognition proteins of the classical and lectin pathways, associated proteases, convertases, regulators and terminal components, with an emphasis on autoantibodies clearly involved in clinical conditions.
Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of multiple autoantibodies. Antibodies against Ficolin-3 were previously identified in the sera of ...some SLE patients, but their prevalence and significance have not been yet investigated. The aims of this study were to determine the prevalence of anti-ficolin-3 antibodies among SLE patients and to investigate their potential as diagnostic and/or prognostic biomarkers in SLE. In this retrospective study, sera from SLE patients (n = 165) were selected from a preexisting declared biological collection. Samples from healthy controls (n = 48) were matched with SLE sera. Disease activity was determined according to the SLEDAI score. Anti-ficolin-3, anti-dsDNA and anti-C1q antibodies levels were measured in sera by ELISA. First, a highly significant difference was found in the anti-ficolin-3 levels between SLE patients and healthy subjects. Anti-ficolin-3 antibodies were detected as positive in 56 of 165 (34%) SLE patients. The titer of anti-ficolin-3 antibodies was correlated with the SLEDAI score (r = 0.38, p<0.0001). The presence of anti-ficolin-3 antibodies was associated with anti-C1q and anti-dsDNA antibodies. Regarding associations with clinical manifestations, the presence of active lupus nephritis was significantly associated with the presence of anti-ficolin-3 antibodies (p≤0.001). This association with renal involvement was higher with anti-ficolin-3 or anti-C1q antibodies than with other auto-antibodies. Interestingly, the combination of anti-ficolin-3 and anti-C1q antibodies demonstrated higher specificity than any other serological biomarker. These results suggest that anti-ficolin-3 antibodies could be useful for the diagnosis of active nephritis in SLE patients.
Objective
Systemic lupus erythematosus (SLE) is a multisystem inflammatory disease characterized by the production of various autoantibodies. The aim of this study was to investigate the presence of ...anti–ficolin‐2 antibodies in SLE patients and to evaluate the association between the levels of these autoantibodies, clinical manifestations, and disease activity.
Methods
This is a comparative study using a cohort of 165 SLE patients and 48 healthy subjects. SLE patients were further divided into 2 groups (low disease activity SLE Disease Activity Index (SLEDAI) score ≤4, n = 88 and high disease activity SLEDAI score >4, n = 77). Clinical manifestations were defined according to the physician in charge. Active lupus nephritis (LN) was documented by kidney biopsy. Detection of anti–ficolin‐2 antibodies was performed by enzyme‐linked immunosorbent assay.
Results
Levels of anti–ficolin‐2 autoantibodies were significantly higher in SLE patients as compared to healthy subjects and associated with SLEDAI score. They were found to be positive in 61 of 165 SLE patients (37%). The presence of anti–ficolin‐2 antibodies was significantly related only to renal involvement, with a very high prevalence (86%) of anti–ficolin‐2 antibodies in SLE patients with active LN. Patients with active proliferative LN had significantly more positive anti–ficolin‐2 antibodies than those with nonproliferative LN. The combination of anti–ficolin‐2, anti–ficolin‐3, and anti‐C1q demonstrated a very high specificity (98%) for the diagnosis of active LN.
Conclusion
Our results support the usefulness of anti–ficolin‐2 as a complementary serologic biomarker for the diagnosis of active lupus with renal manifestations.
Background
The SARS-CoV-2 infection triggers excessive immune response resulting in increased levels of pro-inflammatory cytokines, endothelial injury, and intravascular coagulopathy. The complement ...system (CS) activation participates to this hyperinflammatory response. However, it is still unclear which activation pathways (classical, alternative, or lectin pathway) pilots the effector mechanisms that contribute to critical illness. To better understand the immune correlates of disease severity, we performed an analysis of CS activation pathways and components in samples collected from COVID-19 patients hospitalized in Grenoble Alpes University Hospital between 1 and 30 April 2020 and of their relationship with the clinical outcomes.
Methods
We conducted a retrospective, single-center study cohort in 74 hospitalized patients with RT-PCR-proven COVID-19. The functional activities of classical, alternative, and mannose-binding lectin (MBL) pathways and the antigenic levels of the individual components C1q, C4, C3, C5, Factor B, and MBL were measured in patients’ samples during hospital admission. Hierarchical clustering with the Ward method was performed in order to identify clusters of patients with similar characteristics of complement markers. Age was included in the model. Then, the clusters were compared with the patient clinical features: rate of intensive care unit (ICU) admission, corticoid treatment, oxygen requirement, and mortality.
Results
Four clusters were identified according to complement parameters. Among them, two clusters revealed remarkable profiles: in one cluster (n = 15), patients exhibited activation of alternative and lectin pathways and low antigenic levels of MBL, C4, C3, Factor B, and C5 compared to all the other clusters; this cluster had the higher proportion of patients who died (27%) and required oxygen support (80%) or ICU care (53%). In contrast, the second cluster (n = 19) presented inflammatory profile with high classical pathway activity and antigenic levels of complement components; a low proportion of patients required ICU care (26%) and no patient died in this group.
Conclusion
These findings argue in favor of prominent activation of the alternative and MBL complement pathways in severe COVID-19, but the spectrum of complement involvement seems to be heterogeneous requiring larger studies.
Detection of circulating anti‐GBM antibodies has a key role for the diagnosis of Goodpasture syndrome but immunoassays using purified or recombinant alpha3(IV)NC1 as antigen do not recognize all ...anti‐GBM antibodies. We show that anti‐GBM antibodies directed against epitopes in their native conformation or cryptic epitopes are detected by indirect immunofluorescence.
A precise identification and phenotypic characterization of human B-cell subsets is of crucial importance in both basic research and medicine. In the literature, flow cytometry studies for the ...phenotypic characterization of B-lymphocytes are mainly focused on the description of a particular cell stage, or of specific cell stages observed in a single type of sample. In the present work, we propose a backbone of 6 antibodies (CD38, CD27, CD10, CD19, CD5 and CD45) and an efficient gating strategy to identify, in a single analysis tube, a large number of B-cell subsets covering the whole B-cell differentiation from precursors to memory and plasma cells. Furthermore, by adding two antibodies in an 8-color combination, our approach allows the analysis of the modulation of any cell surface marker of interest along B-cell differentiation. We thus developed a panel of seven 8-colour antibody combinations to phenotypically characterize B-cell subpopulations in bone marrow, peripheral blood, lymph node and cord blood samples. Beyond qualitative information provided by biparametric representations, we also quantified antigen expression on each of the identified B-cell subsets and we proposed a series of informative curves showing the modulation of seventeen cell surface markers along B-cell differentiation. Our approach by flow cytometry provides an efficient tool to obtain quantitative data on B-cell surface markers expression with a relative easy-to-handle technique that can be applied in routine explorations.
Summary
The complement system has been implicated in several kidney diseases, such as antibody‐mediated rejection after kidney transplantation. Antibody‐depletion techniques allow successful ABO‐ ...and/or HLA‐incompatible transplantation. Considering the IgG removal, the use of semi‐selective immunoadsorption (IA) has been advocated. However, because of results on incomplete IgM depletion, the adjunctive use of membrane filtration (MF) has been proposed to enhance the removal of macromolecules and to interfere with complement activation. This secondary endpoint analysis of a recently published randomized, controlled, cross‐over trial was designed to investigate the effect of combined treatment IA + MF compared to IA alone on complement depletion. Two treatment sequences, a single session of IA + MF followed by IA (and vice versa), were analyzed with regard to C5b‐9, properdin, and mannose‐binding lectin (MBL) levels. Neither IA alone nor IA + MF provoked complement activation as demonstrated by stable low levels of C5b‐9 after the procedure as compared to the previous. The combined treatment substantially lowered properdin (77% vs. 26% reduction, P < 0.0001) as well as MBL concentrations (81% vs. 11% reduction, P < 0.0001). Recovery of properdin and MBL levels appears to be longer after IA alone compared to IA + MF. Depletion of properdin and MBL levels may have potential clinical implications in the setting of kidney transplantation.
Lupus nephritis (LN) is one of the most frequent and severe manifestations of systemic lupus erythematosus (SLE), considered as the major predictor of poor prognosis. An early diagnosis of LN is a ...real challenge in the management of SLE and has an important implication in guiding treatments. In clinical practice, conventional parameters still lack sensitivity and specificity for detecting ongoing disease activity in lupus kidneys and early relapse of nephritis. LN is characterized by glomerular kidney injury, essentially due to deposition of immune complexes involving autoantibodies against cellular components and circulating proteins. One of the possible mechanisms of induction of autoantibodies in SLE is a defect in apoptotic cells clearance and subsequent release of intracellular autoantigens. Autoantibodies against soluble protective molecules involved in the uptake of dying cells, including complement proteins and pentraxins, have been described. In this review, we present the main autoantibodies found in LN, with a focus on the antibodies against these protective molecules. We also discuss their pathogenic role and conclude with their potential interest as serological biomarkers in LN.
•Lupus nephritis (LN) is one of the most common and severe manifestations of systemic lupus erythematosus (SLE).•Kidney injury in LN is mediated by the glomerular deposition of pathogenic immune complexes.•Conventional parameters lack sensitivity and specificity for LN diagnosis and prognosis, hence the need for new biomarkers.•Autoantibodies against cellular components and circulating innate immune proteins have been identified in LN.•Predicting the activity of lupus nephritis will require testing a panel of autoantibodies.
Suspicion of myelodysplastic syndromes (MDS) is one of the commonest reasons for bone marrow aspirate in elderly patients presenting with persistent peripheral blood (PB) cytopenia of unclear ...etiology. A PB assay that accurately rules out MDS would have major benefits. The diagnostic accuracy of the intra-individual robust coefficient of variation (RCV) for neutrophil myeloperoxidase (MPO) expression measured by flow cytometric analysis in PB was evaluated in a retrospective derivation study (44 MDS cases and 44 controls) and a prospective validation study (68 consecutive patients with suspected MDS). Compared with controls, MDS cases had higher median RCV values for neutrophil MPO expression (40.2%
30.9%;
<0.001). The area under the receiver operating characteristic curve estimates were 0.94 95% confidence interval (CI): 0.86-0.97 and 0.87 (95%CI: 0.76-0.94) in the derivation and validation studies, respectively. A RCV lower than 30% ruled out MDS with 100% sensitivity (95%CI: 78-100%) and 100% negative predictive value (95%CI: 83-100%) in the prospective validation study. Neutrophil MPO expression measured by flow cytometric analysis in PB might obviate the need for invasive bone marrow aspirate and biopsy for up to 29% of patients with suspected MDS.
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