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

BACKGROUND Glomerular deposition of IgA1 is a common feature of Henoch-Schönlein 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-Schönlein purpura, the binding of Vicia villosa lectin to serum IgA1 was studied in the following subject groups: IgA nephropathy; adults and children with Henoch-Schönlein purpura and nephritis; children with clinically diagnosed Henoch-Schönlein 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-Schönlein purpura with nephritis. However, the lectin binding of serum IgA1 from children with Henoch-Schönlein 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-Schönlein 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.