528
Views
5
CrossRef citations to date
0
Altmetric
Original Article

Gain of function mutant of complement factor B K323E mimics pathogenic C3NeF autoantibodies in convertase assays

, , , , , & show all
Pages 18-24 | Received 14 Aug 2017, Accepted 29 Dec 2017, Published online: 08 Jan 2018
 

Abstract

Complement convertases are enzymatic complexes, which play a critical role in propagation and amplification of the complement cascade. Under physiological conditions, convertases decay shortly after being formed in either spontaneous or inhibitor-driven process. Prolongation of their half-life by C3NeF autoantibodies that prevent convertase dissociation results in pathogenic condition often manifested by renal diseases. However, the diagnosis of convertase abnormalities is difficult due to the labile nature of these enzymes and low credibility of existing methods. Only recently, two-step functional assays employing C5-depleted serum or C5 inhibitors were introduced. Their advantage is convertase formation in the physiological milieu of whole serum and the drawback is inter-assay variability due to variations in rabbit erythrocytes used for the haemolysis-based readout. Abovementioned problems demand the application of the internal standard in each experiment. Obtaining a defined preparation of autoantibodies is complicated due to ethical and practical considerations. We found that recombinant, his-tagged factor B (fB) variant K323E retains full hemolytic activity and possess the ability to form convertases with prolonged half-life either in fB-depleted serum or when mixed with normal human serum. Such dominant character of K323E mutation allows using recombinant protein as a reference in functional convertase assays, not limited to these using rabbit erythrocytes. Additionally, our results demonstrate that gain of function mutations in complement components mimic the phenotype of C3NeF. Hence, patients with such “genetic C3NeF” would not benefit from B-cell depletion (e.g. by rituximab) and therefore should be properly diagnosed in order to choose suitable therapeutic intervention.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

This work was supported by the grants from the National Science Centre Poland (NCN, grant no. 2015/18/M/NZ6/00334) Dutch Kidney Foundation (CP 14.27 COMBAT consortium, 13OI116, KFB 11.007, IP 10.22, 160KKO1), the European Renal Association – European Dialysis and Transplantation Association (grants ERA STF 138-2013, ERA LTF 203-2014), and the European Society for Pediatric Nephrology (grant 2014.03).

Reprints and Corporate Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

To request a reprint or corporate permissions for this article, please click on the relevant link below:

Academic Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

Obtain permissions instantly via Rightslink by clicking on the button below:

If you are unable to obtain permissions via Rightslink, please complete and submit this Permissions form. For more information, please visit our Permissions help page.