Electric charge and sugar chains of immunoglobulin G in systemic lupus erythematosus

Abstract

The charge condition of anti-DNA antibody is thought to be closely related to the pathology of renal disorders in systemic lupus erythematosus (SLE). We examined the relationships among the electric charge of IgG, proteinuria, and DNA binding capacity in SLE patients. Abnormal sugar chains, which affect the IgG charge, were also studied. IgG in SLE patients with proteinuria had a higher positive electric charge than that in SLE patients without proteinuria, healthy individuals, and patients with other collagen diseases. Anti-DNA antibody titers measured by enzyme-linked immunosorbent assay (ELISA) were high in the positive charge regions of the IgG fractions obtained by a cationic exchange column. The binding capacity of double-stranded (ds)DNA measured by the Farr assay tended to be present specifically in the positive charge region in SLE patients with proteinuria. In affinoblotting using lectins, the percentage of IgG deficient in negative-charged sugar chains was found to be high in patients with a preponderant positive charge on anti-DNA antibody. Abnormal IgG-bound sugar chains result in a preponderantly positive charge and are involved in the etiology of SLE nephritis.