Protein A immunoadsorption cannot significantly remove the soluble receptor of urokinase from sera of patients with recurrent focal segmental glomerulosclerosis

Abstract

Background. Focal segmental glomerulosclerosis (FSGS) is a serious disease, the pathogenesis of which is unknown. Its recurrence after transplantation (Tx) and its partial remission after treatment with immunoadsorption (IA) on a protein A column indicate the existence of a circulating factor responsible for the disease that is able to bind to a protein A column. Recently, the soluble receptor of urokinase (suPAR) was described as the factor responsible for FSGS. We tested the capacity of suPAR to bind to protein A and to be eliminated by IA. Methods. We measured suPAR in eluates of protein A columns from seven patients with recurrent FSGS after Tx (rFSGS) treated with IA, and in the serum of 13 patients with rFSGS and 11 healthy donors (HDs). Additionally, the plasma of these patients was immunoadsorbed in vitro on a protein A Sepharose column, and we quantified suPAR in the eluates and in pre- and post-column samples. Results. The concentration of suPAR was higher in the plasma of patients with rFSGS than that of HD patients. However, the concentration of suPAR was similar before and after IA on protein A for the rFSGS and HD samples. The suPAR concentration was very low in the eluates from protein A columns incubated with plasma from HD or rFSGS patients. However, 85% of rFSGS patients showed a decrease in immunoglobulin G and proteinuria. Conclusions. Thus, suPAR does not significantly bind to protein A in vitro or in vivo. © The Author 2013. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.