Development of a Polyclonal Antibody Against Synthetic Human Immunoglobulin A1 Hinge Glycopeptide

Background: Undergalactosylated IgA1 has been found to be increased in IgA nephropathy (IgAN) by an ELISA assay using Helix aspersa agglutinin (HAA) that recognizes N-acetylgalactosamine (GalNAc). In this study, we developed a polyclonal antibody (anti-sHGP antibody) against a synthetic IgA1 hinge peptide with five GalNAc residues. Methods: The specificity of the anti-sHGP antibody was evaluated through the incremental treatment of IgA with corresponding glycosidases. Then, the susceptibility of the IgA to anti-sHGP antibody was compared among IgAN patients (n=39), patients with other forms of kidney diseases (OKD, n= 36) and healthy controls (n=37), using ELISA assay. The association of the binding abilities between anti-sHGP antibody and HAA were evaluated blindly using same 85 sera. Results: The binding ability of the anti-sHGP antibody was increased relative to the incremental treatments of neuraminidase (desialo-IgA), galactosidase (desialo/degalacto IgA). The binding levels of anti-sHGP antibody against serum IgA were significantly higher in IgAN patients compared to both healthy controls (P=0.008) and those with OKD (P=0.049). The binding levels of anti-sHGP antibody were closely related to those of HAA ELISA in the same patient sera (RR2=0.5964). Conclusions: It was certified that the anti-sHGP antibody recognized GalNAc residues in the hinge peptide of human IgA1 as well as HAA. The increased antigenicity of IgA against the antibody in IgAN suggested that a serum IgA1 exposing GalNAc residue was increased in IgAN. It would be necessary to identify the precise structure of O-glycans specific to IgAN for developing a more specific antibody.