Quantitative multiplex profiling of the complement system to diagnose complement‐mediated diseases

Abstract

Objectives Complement deficiencies are difficult to diagnose because of the variability of symptoms and the complexity of the diagnostic process. Here, we applied a novel ‘complementomics’ approach to study the impact of various complement deficiencies on circulating complement levels. Methods Using a quantitative multiplex mass spectrometry assay, we analysed 44 peptides to profile 34 complement proteins simultaneously in 40 healthy controls and 83 individuals with a diagnosed deficiency or a potential pathogenic variant in 14 different complement proteins. Results Apart from confirming near or total absence of the respective protein in plasma of complement‐deficient patients, this mass spectrometry‐based profiling method led to the identification of additional deficiencies. In many cases, partial depletion of the pathway up‐ and/or downstream of the absent protein was measured. This was especially found in patients deficient for complement inhibitors, such as angioedema patients with a C1‐inhibitor deficiency. The added value of complementomics was shown in three patients with poorly defined complement deficiencies. Conclusion Our study shows the potential clinical utility of profiling circulating complement proteins as a comprehensive read‐out of various complement deficiencies. Particularly, our approach provides insight into the intricate interplay between complement proteins due to functional coupling, which contributes to the better understanding of the various disease phenotypes and improvement of care for patients with complement‐mediated diseases.

Complement factor D haplodeficiency is associated with a reduced complement activation speed and diminished bacterial killing

“…For patient A, significant lower levels of C1 inhibitor, C3, C5 and vitronectin were detected. 10 In addition, and especially relevant for complement deficiencies that can be compensated by sufficient CP activation, nasopharyngeal colonisation or subclinical infections induce immunisation that would protect against reinfection.…”

“…Analysis of 34 complement proteins in serum by mass spectrometry revealed undetectable fD and significant lower C1 inhibitor, C3, C5 and vitronectin serum level. 10 Genetic analysis of complement genes revealed a maternal heterozygous NM_001928.3(CFD):c.125C>A p.(Ser42*) gene mutation. Additional analysis of 386 primary immunodeficiency genes using clinical exome sequencing was further normal.…”

“…Analysis of 34 complement proteins in serum by mass spectrometry revealed undetectable fD. 10 Genetic analysis of complement genes demonstrated the familial heterozygous fD mutation. Following diagnosis, she was started on co-trimoxazole prophylaxis and received additional pneumococcal, meningococcal ACYW and 4CMenB vaccines.…”

Expanding Horizons in Complement Analysis and Quality Control

“…Another area of recent advancement is the potential to gain information by multiplexing complement testing. As complement is a cascade of multiple pathways and multiple components, the value of being able to test across the pathways is clear ( 84 ). An example of the potential value of this type of approach is presented in the work of Lennart Hammarström of the Karolinska Institute that has pioneered using dried blood spot samples in conjunction with multiplex immunoassays to detect primary complement deficiencies ( 85 ).…”

“…An example of the potential value of this type of approach is presented in the work of Lennart Hammarström of the Karolinska Institute that has pioneered using dried blood spot samples in conjunction with multiplex immunoassays to detect primary complement deficiencies ( 85 ). Taking another approach, the group led by Marien I. de Jonge has demonstrated success using mass spectrometry to profile the complement system ( 84 ). These early successes are likely only the start of future multiplex testing in the complement laboratory.…”