Incompleteness of mucin-type sugar chain of human serum IgA1 as possible cause of IgA nephropathy

IgA nephropathy is characterized by IgA deposits in the renal glomerular mesangium and occurs quite frequently as primary glomerulonephritis in many people. This disease is thought to be due to the deposition of an immune complex consisting of a foreign antigen and polymerized IgAl in the glomeruli. An examination was made to determine why the IgAl subclass, among many immunoglobulins, is deposited primarily in the glomeruli, by directing attention to structural defects in the IgAl molecule, particularly the aberrant mucin-type sugar chain on the hinge portion [Iwase, H., et al., TIGG 10, 13-22 (1998)]. It was concluded based on our recent results that incompleteness of the mucin-type sugar chain of human serum IgA1 causes IgA nephropathy. The authors would appreciate critical and suggestive advice for future studies on IgA nephropathy. Of course, the above conclusion remains to be fully confirmed. This would require the removal of abnormal IgAl molecules from serum to result in the recovery of patients of IgA nephropathy.