Binding capacity of in vitro deglycosylated IgA1 to human mesangial cells

IgA nephropathy (IgAN) is the most common glomerular disease and it is characterized by deposition of IgA1 molecules in mesangium. Recent studies had demonstrated that serum and mesangial IgA1 in IgAN were deglycosylated and IgA1 could bind to human mesangial cells (HMC) through a novel receptor. The aim of the current study is to investigate and compare the binding capacities of different in vitro deglycosylated IgA1 on human mesangial cells. Serum IgA1 was purified by jacalin affinity chromatography and then was desialylated (DesIgA1) and/or degalactosylated (Des/DeGalIgA1) with neuraminidase and/or beta-galactosidase. The efficacy of deglycosylations was assessed by Peanut agglutinin (PNA) and Vicia villosa (VV) lectin. The sizes of normal IgA1 and deglycosylated IgA1 were determined by Sephacryl S-300 chromatography and binding capacities to primary HMC were evaluated by radioligand binding assays. Normal IgA1 and deglycosylated IgA1 could bind to HMC in a dose-dependent, saturable manner. The maximal binding capacities and binding sites/cell of DesIgA1 and Des/DeGalIgA were significantly higher than that of normal IgA1. However, more aggregated IgA1 was found in DesIgA1 and Des/DeGalIgA1. Scatchard analysis revealed a similar Kd of normal IgA1 and deglycosylated IgA1. The current study suggested that the binding capacities of DesIgA1 and Des/DeGalIgA1 to HMC were significantly higher than that of normal IgA1, which at least in part was due to more macromolecular IgA1 in deglycoslated IgA1. However, there were no significant differences in the affinities of normal IgA1, DesIgA1 and Des/DeGalIgA1 with HMC. Deglycosylated IgA1 might play an important role in pathogenesis of IgAN.