Clinical Complement Analysis-An Overview

External quality assurance program for diagnostic complement laboratories: evaluation of the results of the past seven years

Introduction

The complement external quality assurance (EQA) program was first organized in 2010 by a group of researchers working in diagnostic complement laboratories. Starting in 2016, INSTAND e.V., a German, non-profit interdisciplinary scientific medical society dedicated to providing expert EQA programs for medical laboratories, started organizing the EQAs for complement diagnostic laboratories together with the same group of experienced scientists and doctors who also work as EQA experts. The aim of the current work is to provide descriptive analysis of the past seven years' complement EQA results and evaluate timeline changes in proficiency testing.

Methods

Each year, in March and October, blinded samples (normal, pathological) were sent to the participating diagnostic laboratories, where complement parameters were evaluated exactly as in daily routine samples. Since no reference method/target values exist for these parameters, and participants used different units for measurement, the reported results were compared to the stable mean (Algorithm A) of the participants using the same method/measurement units. A reported result was qualified as "passed" if it fell into the 30-50% evaluation/target range around the mean of reported results (depending on the given parameter).

Results

While the number of participating laboratories has increased in the past years (from around 120 to 347), the number of complement laboratories providing multiple determinations remained mostly unchanged (around 30 worldwide). C3, C4, C1-inhibitor antigen and activity determinations provided the best proficiency results, with >90% passing quotas in the past years, independent of the applied method. Determination of the functional activity of the three activation pathways was good in general, but results showed large variance, especially with the pathological samples. Complement factor C1q and regulators FH and FI are determined by only a few laboratories, with variable outcomes (in general in the 85-90% pass range). Activation products sC5b-9 and Bb were determined in 30 and 10 laboratories, respectively, with typical passing quotas in the 70-90% range, without a clear tendency over the past years.

Conclusion

With these accumulated data from the past seven years, it is now possible to assess sample-, method-, and evaluation related aspects to further improve proficiency testing and protocolize diagnostic complement determinations.

Dissociation Phenomenon of Erythrocyte Agglutination and Its Application to Assay of Functional Activity of the Complement System in Clinical Laboratory

OBJECTIVE

The objective of the study was to validate the dissociation phenomenon of erythrocyte agglutination which is based on erythrocyte fragments and to apply it in the functional activity assay of the complement system.

METHODS

The dissociation-agglutination effect of erythrocyte fragments was validated by detecting the number of free erythrocytes after the action of erythrocyte fragments on agglutinated erythrocytes. The number of free erythrocytes produced after hemolysis of agglutinated erythrocytes caused by complements and complement activators(CAs) was detected by auto hematology analyzer and the results were indicated by mean hemoglobin concentration of erythrocytes (MCHC). We optimized the test conditions and validated the inter-batch stability, explored the resolution of the assay method, and assayed for the total complement activity (AC) and the CAs activated complement activity (ACA) in serum from patients and healthy individual groups.

RESULTS

Erythrocyte fragments have a dissociative effect on agglutinated erythrocytes. The auto hematology analyzer was able to detect AC and ACA, where AC showed an inverse correlation with MCHC, and ACA demonstrated a positive correlation with MCHC. The inter-batch CV of AC, ACA, and ACA/AC was found to be 5%, 9%, and 11.7%, respectively, with good stability. The study found that serum samples from acute phase reaction patients showed significant differences in ACA compared with healthy individuals, with a p value of 0.018; serum samples from patients with nephrotic syndrome showed significant differences in AC, ACA, and ACA/AC compared with healthy individuals, with p values of 0.014, 0.002, and 0.041, respectively.

CONCLUSION

Erythrocyte fragments have dissociation-agglutination effect. The complement system immunological functional detection method, based on this effect, has potential clinical application value due to its sensitivity and accuracy.

Zinc Supplementation Induced Transcriptional Changes in Primary Human Retinal Pigment Epithelium: A Single-Cell RNA Sequencing Study to Understand Age-Related Macular Degeneration

Zinc supplementation has been shown to be beneficial to slow the progression of age-related macular degeneration (AMD). However, the molecular mechanism underpinning this benefit is not well understood. This study used single-cell RNA sequencing to identify transcriptomic changes induced by zinc supplementation. Human primary retinal pigment epithelial (RPE) cells could mature for up to 19 weeks. After 1 or 18 weeks in culture, we supplemented the culture medium with 125 µM added zinc for one week. RPE cells developed high transepithelial electrical resistance, extensive, but variable pigmentation, and deposited sub-RPE material similar to the hallmark lesions of AMD. Unsupervised cluster analysis of the combined transcriptome of the cells isolated after 2, 9, and 19 weeks in culture showed considerable heterogeneity. Clustering based on 234 pre-selected RPE-specific genes divided the cells into two distinct clusters, we defined as more and less differentiated cells. The proportion of more differentiated cells increased with time in culture, but appreciable numbers of cells remained less differentiated even at 19 weeks. Pseudotemporal ordering identified 537 genes that could be implicated in the dynamics of RPE cell differentiation (FDR < 0.05). Zinc treatment resulted in the differential expression of 281 of these genes (FDR < 0.05). These genes were associated with several biological pathways with modulation of ID1/ID3 transcriptional regulation. Overall, zinc had a multitude of effects on the RPE transcriptome, including several genes involved in pigmentation, complement regulation, mineralization, and cholesterol metabolism processes associated with AMD.

The complement system testing in clinical laboratory

With the advancement in research in the field of the complement system, a more comprehensive understanding developed about the complement system's role in the life process of an organism. It is a system of innate immune surveillance. This system plays a pivotal role in host defense against pathogens, inflammation, B and T cell homeostasis. Complement system analysis has a significant advantage in the assessment of the immune system status, diagnosis and prognosis of diseases, and medication guidelines. Currently, complement system testing is neither yet widely used across all clinical laboratoriesnor are the testing protocols yet systematic. Based on the current research, it is suggested that the analysis of complement activator-activated complement activity and total complement activity would be comprehensively assessed to evaluate the complement system's immunological function, and combine of the detection of its components to establish a systematic protocol for the complement system testing in the clinical laboratory. This article reviews the complement system's physiological role, disease relevance and the current testing status in clinical laboratories. Further more, some suggestions have also been provided for the preparation of complement standards i.e., the standardized preparation process for complement standards seems to be a feasible option given the easy inactivation of complement.

Inter-Individual Variations: A Challenge for the Standardisation of Complement Activation Assays

Introduction

The role of the human immune system in pathologic responses to chemicals including nanomaterials was identified as a gap in current hazard assessments. However, the complexity of the human immune system as well as interspecies variations make the development of predictive toxicity tests challenging. In the present study, we have analysed to what extent fluctuations of the complement system of different individuals will have an impact on the standardisation of immunological tests.

Methods

We treated commercially available pooled sera (PS) from healthy males, individual sera from healthy donors and from patients suffering from cancer, immunodeficiency and allergies with small molecules and liposomes. Changes of iC3b protein levels measured in enzyme-linked immunosorbent assays served as biomarker for complement activation.

Results

The level of complement activation in PS differed significantly from responses of individual donors (p < 0.01). Only seven out of 32 investigated sera from healthy donors responded similarly to the pooled serum. This variability was even more remarkable when investigating the effect of liposomes on the complement activation in sera from donors with pre-existing pathologies. Neither the 26 sera of donors with allergies nor sera of 16 donors with immunodeficiency responded similar to the PS of healthy donors. Allergy sufferers showed an increase in iC3b levels of 4.16-fold changes when compared to PS treated with liposomes.

Discussion

Our studies demonstrate that the use of pooled serum can lead to an over- or under-estimation of immunological response in particular for individuals with pre-existing pathologies. This is of high relevance when developing medical products based on nanomaterials and asks for a review of the current practice to use PS from healthy donors for the prediction of immunological effects of drugs in patients. A better understanding of individual toxicological responses to xenobiotics should be an essential part in safety assessments.

Elevated plasma complement components in facioscapulohumeral dystrophy

Advances in understanding the pathophysiology of facioscapulohumeral dystrophy (FSHD) have led to several therapeutic approaches entering clinical trials and an increased need to develop biomarkers of disease activity and progression. Multiple prior studies have shown early elevation of RNAs encoding components of the complement pathways and relatively widespread activated complement complexes by immunodetection in FSHD muscle. The current study tested plasma from two independent cohorts of FSHD and control subjects and found elevated complement components in both FSHD cohorts. Combining subjects from both cohorts identified complement factors that best distinguished FSHD and controls. Within the FSHD group, a subset of subjects showed elevation in multiple complement components. Together these findings suggest the need for future studies to determine whether measurements of complement activation can be used as a non-invasive measurement of FSHD disease activity, progression and/or response to therapies. In addition, with the ongoing expansion of complement therapeutic approaches, consideration for precision-based targeting of this pathway is appropriate.

Complement in Secondary Thrombotic Microangiopathy

Thrombotic microangiopathy (TMA) is a condition characterized by thrombocytopenia and microangiopathic hemolytic anemia (MAHA) with varying degrees of organ damage in the setting of normal international normalized ratio and activated partial thromboplastin time. Complement has been implicated in the etiology of TMA, which are classified as primary TMA when genetic and acquired defects in complement proteins are the primary drivers of TMA (complement-mediated TMA or atypical hemolytic uremic syndrome, aHUS) or secondary TMA, when complement activation occurs in the context of other disease processes, such as infection, malignant hypertension, autoimmune disease, malignancy, transplantation, pregnancy, and drugs. It is important to recognize that this classification is not absolute because genetic variants in complement genes have been identified in patients with secondary TMA, and distinguishing complement/genetic-mediated TMA from secondary causes of TMA can be challenging and lead to potentially harmful delays in treatment. In this review, we focus on data supporting the involvement of complement in aHUS and in secondary forms of TMA associated with malignant hypertension, drugs, autoimmune diseases, pregnancy, and infections. In aHUS, genetic variants in complement genes are found in up to 60% of patients, whereas in the secondary forms, the finding of genetic defects is variable, ranging from almost 60% in TMA associated with malignant hypertension to less than 10% in drug-induced TMA. On the basis of these findings, a new approach to management of TMA is proposed.

Complement system network in cell physiology and in human diseases

The complement system is a multi-functional system representing the first line host defense against pathogens in innate immune response, through three different pathways. Impairment of its function, consisting in deficiency or excessive deregulated activation, may lead to severe systemic infections or autoimmune disorders. These diseases may be inherited or acquired. Despite many diagnostic tools are currently available, ranging from traditional, such as hemolytic or ELISA based assays, to innovative ones, like next generation sequencing techniques, these diseases are often not recognized. As for therapeutic aspects, strategies based on the use of targeted drugs are now widespread. The aim of this review is to present an updated overview of complement system pathophysiology, clinical implications of its dysfunction and to summarize diagnostic and therapeutic approaches.

Complement Receptor 2 Based Immunoassay Measuring Activation of the Complement System at C3-Level in Plasma Samples From Mice and Humans

We aimed at establishing a sensitive and robust assay for estimation of systemic complement activation at complement component C3 level in mouse and human plasma samples. In order to capture the activation products iC3b and C3dg in a specific and physiological relevant manner we utilized a construct consisting of the iC3b/C3dg-binding site of human complement receptor 2 (CR2) attached to an Fc-part of mouse IgG. This construct binds C3dg and iC3b from both mice and humans. We purified the CR2-IgG construct from mouse B myeloma cell line supernatants, J558L-CR2-IgG, by protein G affinity chromatography. The CR2-IgG construct was used for capturing C3 fragments in microtiter wells and an anti-mouse or an anti-human-C3 antibody was used for detection of bound C3 fragments. Initially we tested the specificity of the assays with the use of purified C3 fragments. Further, with the use of the CR2-based assay, we measured an up to three-fold higher signal in activated mouse serum as compared to non-activated mouse serum, whereas activated serum from a C3 knock-out mouse gave no signal. We tested in vivo generated samples from a mouse experiment; complement activation was induced by injecting cobra venom factor or heat aggregated IgG into C57bl6 mice, followed by withdrawal of EDTA blood samples at different time points and measurement of iC3b/C3dg. We observed a clear time-dependent distinction in signals between samples with expected high and low complement activation. Furthermore, with the use of the assay for human C3 fragments, we observed that patients with systemic lupus erythematosus (SLE) (n = 144) had significantly higher iC3b/C3dg levels as compared to healthy individuals (n = 144) (p < 0.0001). We present two functional immunoassays, that are able to measure systemic levels of the C3-activation products iC3b and C3dg in mice and humans. To our knowledge, these are the first assays for complement activation that use a physiological relevant capture construct such as CR2. These assays will be a relevant tool when investigating mouse models and human diseases involving the complement system.