Expanding Horizons in Complement Analysis and Quality Control

Abstract

Complement not only plays a key role in host microbial defense but also modulates the adaptive immune response through modification of T- and B-cell reactivity. Moreover, a normally functioning complement system participates in hematopoiesis, reproduction, lipid metabolism, and tissue regeneration. Because of its powerful inflammatory potential, multiple regulatory proteins are needed to prevent potential tissue damage. In clinical practice, dysregulation and overactivation of the complement system are major causes of a variety of inflammatory and autoimmune diseases ranging from nephropathies, age-related macular degeneration (AMD), and systemic lupus erythematosus (SLE) to graft rejection, sepsis, and multi-organ failure. The clinical importance is reflected by the recent development of multiple drugs targeting complement with a broad spectrum of indications. The recognition of the role of complement in diverse diseases and the advent of complement therapeutics has increased the number of laboratories and suppliers entering the field. This has highlighted the need for reliable complement testing. The relatively rapid expansion in complement testing has presented challenges for a previously niche field. This is exemplified by the issue of cross-reactivity of complement-directed antibodies and by the challenges of the poor stability of many of the complement analytes. The complex nature of complement testing and increasing clinical demand has been met in the last decade by efforts to improve the standardization among laboratories. Initiated by the IUIS/ICS Committee for the Standardization and Quality Assessment in Complement Measurements 14 rounds of external quality assessment since 2010 resulted in improvements in the consistency of testing across participating institutions, while extending the global reach of the efforts to more than 200 laboratories in 30 countries. Worldwide trends of assay availability, usage, and analytical performance are summarized based on the past years’ experiences. Progress in complement analysis has been facilitated by the quality assessment and standardization efforts that now allow complement testing to provide a comprehensive insight into deficiencies and the activation state of the system. This in turn enables clinicians to better define disease severity, evolution, and response to therapy.

The Role of Complement in HSCT-TMA: Basic Science to Clinical Practice

“…As more laboratories begin to adopt the use of biomarkers such as sC5b-9 in HSCT-TMA, testing capability and availability should improve [47,66,67]. Indeed, many groups, such as the International Union of Immunological Sciences and International Complement Society (IUIS/ICS) Committee for the Standardization and Quality Assessment in Complement Measurements, have been working in this direction [68]. Others have also suggested that biomarkers, such as the factor B activation product Ba, may show utility in HSCT-TMA [69].…”

Pitfalls in complement analysis: A systematic literature review of assessing complement activation

“…This need for standardization and well-defined and characterized assays is well-known within the field. It is therefore that in 2009, the Sub-Committee for the Standardization and Quality Assessment of Complement Measurements (the ‘Complement EQA Group’) was formally recognized and became part of the IUIS (International Union of Immunological Societies) Quality Assessment and Standardization Committee ( ) ( 2 , 82 ). Next to that, the Complement EQA Group is a standing committee also of the International Complement Society (ICS).…”

“…Next to that, the Complement EQA Group is a standing committee also of the International Complement Society (ICS). The purpose of the EQA group is to facilitate standardized diagnostic complement analysis by developing calibrator materials and test recommendations ( 2 , 82 ). Initial steps have been made as a serum standard to be used as calibrator for quantitative and functional complement analysis in normal, non-activated human serum (Standard 1; ICS#1) was prepared and evaluated.…”

“…Interestingly, assessment of complement within these fields is often performed using incorrect or suboptimal assays and samples that were inappropriate handled regarding collection, storage and pre-analytical preparations ( 80 ). As complement is involved in an increasing number of human diseases, standardized measurement of complement components is essential ( 1 – 5 , 82 ). However, accurate determination of the complement status of individual patients has proven still to be challenging and needs to be performed in a uniform way.…”

“…For analysis of individual complement components, EDTA-plasma should be used having at least a final concentration of 10 mM ( 82 , 100 ), especially when measuring activation products. Using EDTA-plasma, any further activation of complement is minimized (but not completely excluded) since EDTA chelates Ca 2+ and Mg 2+ thereby blocking the function of the C1 complex and the C3 convertases ( 4 , 83 , 100 – 102 ).…”