Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands

Correspondence: Paul J.M. van der Boog M.D., Department of Nephrology, C3-P, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands. E-mail:p.j.m.van_der_boog@lumc.nl

Received 18 February 2004; Revised 26 May 2004; Accepted 21 October 2004.

Abstract

Role of macromolecular IgA in IgA nephropathy Primary IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis, leading to progressive renal failure in almost one third of the patients. The disease is characterized by mesangial deposits of IgA. The pathogenesis of IgAN remains incompletely understood. The basic abnormality of this disorder lies within the IgA immune system rather than in the kidney. Elevated levels of IgA and IgA-containing complexes are found in sera of most patients with IgAN, but increased levels alone are not sufficient to develop IgAN. Therefore abnormal physicochemical properties of circulating IgA, such as size, charge, and glycosylation may play a role. This is supported by the presence of altered glycosylation of serum and mesangial IgA in patients with IgAN. Although the precise origin and nature of the mesangial IgA deposits are still uncertain, they contain at least in part macromolecular IgA, which may be derived from circulating IgA-containing complexes. Recently, novel insights have been obtained in the molecular composition of circulating high-molecular-weight IgA, which might include complexes with underglycosylated IgA1 and IgA-CD89 complexes. In this review various aspects of macromolecular IgA in relation to IgAN will be discussed.