Abnormal IgA glycosylation in Henoch-Schonlein purpura restricted to patients with clinical nephritis

Background: Glomerular deposition of IgA1 is a common feature of Henoch-Schonlein purpura, and is indistinguishable from that seen in IgA nephropathy. Serum IgA1 is abnormally O-glycosylated in IgA nephropathy, and this may contribute to mesangial IgA1 deposition and the development of glomerular injury. This altered O-glycosylation of IgA1 can be detected by its increased binding to the lectin Vicia villosa. Methods: To investigate whether IgA1 is abnormally glycosylated in Henoch-Schonlein purpura, the binding of Vicia villosa lectin to serum IgA1 was studied in the following subject groups: IgA nephropathy; adults and children with Henoch-Schonlein purpura and nephritis; children with clinically diagnosed Henoch-Schonlein purpura but no renal involvement; adults and children with non-IgA associated glomerulonephritis; and matched controls. Results: The abnormality of lectin binding seen in IgA nephropathy was also found in both adults and children with Henoch-Schonlein purpura with nephritis. However the lectin binding of serum IgA1 from children with Henoch-Schonlein purpura lacking renal involvement did not differ from controls, and similarly no abnormality of lectin binding was seen in patients with non-IgA associated glomerulonephritis. Conclusions: These data indicate that the abnormality of IgA1 O-glycosylation seen in IgA nephropathy is also found in Henoch Schonlein purpura, but only in those subjects with renal involvement, while IgA1 O-glycosylation is normal in patients with other forms of renal disease. These findings lend strong support to a role for altered IgA1 O-glycosylation in the pathogenesis of IgA-associated glomerular disease.