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Overactivity of alternative pathway convertases in patients with complement-mediated renal diseases

Michels, Marloes A.H.M. ; van de Kar, Nicole C.A.J. ; Okrój, Marcin LU ; Blom, Anna M. LU orcid ; van Kraaij, Sanne A.W. ; Volokhina, Elena B. LU and van den Heuvel, Lambertus P.W.J. (2018) In Frontiers in Immunology 9(APR).
Abstract

Overactivation of the alternative pathway of the complement system is associated with the renal diseases atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). C3 nephritic factors (C3NeF) play an important role in C3G pathogenesis by stabilizing the key enzymatic complex of complement, the C3 convertase. However, the reliability of assays detecting these autoantibodies is limited. Therefore, in this study, we validated and optimized a prototype hemolytic method for robust detection and characterization of factors causing convertase overactivity in large patient cohorts. The assay assesses convertase activity directly in the physiological milieu of serum and therefore is not restricted to detection of stabilizing... (More)

Overactivation of the alternative pathway of the complement system is associated with the renal diseases atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). C3 nephritic factors (C3NeF) play an important role in C3G pathogenesis by stabilizing the key enzymatic complex of complement, the C3 convertase. However, the reliability of assays detecting these autoantibodies is limited. Therefore, in this study, we validated and optimized a prototype hemolytic method for robust detection and characterization of factors causing convertase overactivity in large patient cohorts. The assay assesses convertase activity directly in the physiological milieu of serum and therefore is not restricted to detection of stabilizing autoantibodies such as C3NeF but may also reveal genetic variants resulting in prolonged convertase activity. We first defined clear cutoff values based on convertase activity in healthy controls. Next, we evaluated 27 C3G patient samples and found 16 positive for prolonged convertase activity, indicating the presence of factors influencing convertase stability. In three patients, the overactive convertase profile was persistent over disease course while in another patient the increased stability normalized in remission. In all these four patients, the convertase-stabilizing activity resided in the purified immunoglobulin (Ig) fraction, demonstrating the autoantibody nature. By contrast, the Igs of a familial aHUS patient carrying the complement factor B mutation p.Lys323Glu did not reveal convertase stabilization. However, in serum prolonged convertase activity was observed and segregated with the mutation in both affected and unaffected family members. In conclusion, we present a robust and reliable method for the detection, characterization, and evaluation over time of factors prolonging convertase activity (C3NeF or certain mutations) in patient cohorts. This assay may provide new insights in disease pathogenesis and may contribute to the development of more personalized treatment strategies.

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type
Contribution to journal
publication status
published
subject
keywords
Alternative pathway, Atypical hemolytic uremic syndrome, C3 glomerulopathy, C3 nephritic factor, Complement factor B mutation, Complement system, Convertase
in
Frontiers in Immunology
volume
9
issue
APR
article number
612
publisher
Frontiers Media S. A.
external identifiers
  • scopus:85045001166
  • pmid:29670616
ISSN
1664-3224
DOI
10.3389/fimmu.2018.00612
language
English
LU publication?
yes
id
1e8eaaef-f097-4897-b17f-e1f0b52152db
date added to LUP
2018-04-18 16:06:03
date last changed
2021-10-06 05:27:14
@article{1e8eaaef-f097-4897-b17f-e1f0b52152db,
  abstract     = {<p>Overactivation of the alternative pathway of the complement system is associated with the renal diseases atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). C3 nephritic factors (C3NeF) play an important role in C3G pathogenesis by stabilizing the key enzymatic complex of complement, the C3 convertase. However, the reliability of assays detecting these autoantibodies is limited. Therefore, in this study, we validated and optimized a prototype hemolytic method for robust detection and characterization of factors causing convertase overactivity in large patient cohorts. The assay assesses convertase activity directly in the physiological milieu of serum and therefore is not restricted to detection of stabilizing autoantibodies such as C3NeF but may also reveal genetic variants resulting in prolonged convertase activity. We first defined clear cutoff values based on convertase activity in healthy controls. Next, we evaluated 27 C3G patient samples and found 16 positive for prolonged convertase activity, indicating the presence of factors influencing convertase stability. In three patients, the overactive convertase profile was persistent over disease course while in another patient the increased stability normalized in remission. In all these four patients, the convertase-stabilizing activity resided in the purified immunoglobulin (Ig) fraction, demonstrating the autoantibody nature. By contrast, the Igs of a familial aHUS patient carrying the complement factor B mutation p.Lys323Glu did not reveal convertase stabilization. However, in serum prolonged convertase activity was observed and segregated with the mutation in both affected and unaffected family members. In conclusion, we present a robust and reliable method for the detection, characterization, and evaluation over time of factors prolonging convertase activity (C3NeF or certain mutations) in patient cohorts. This assay may provide new insights in disease pathogenesis and may contribute to the development of more personalized treatment strategies.</p>},
  author       = {Michels, Marloes A.H.M. and van de Kar, Nicole C.A.J. and Okrój, Marcin and Blom, Anna M. and van Kraaij, Sanne A.W. and Volokhina, Elena B. and van den Heuvel, Lambertus P.W.J.},
  issn         = {1664-3224},
  language     = {eng},
  month        = {04},
  number       = {APR},
  publisher    = {Frontiers Media S. A.},
  series       = {Frontiers in Immunology},
  title        = {Overactivity of alternative pathway convertases in patients with complement-mediated renal diseases},
  url          = {http://dx.doi.org/10.3389/fimmu.2018.00612},
  doi          = {10.3389/fimmu.2018.00612},
  volume       = {9},
  year         = {2018},
}