Renal extraglomerular vascular immune deposits in IgA glomerulonephritis

Kidney biopsies of 425 patients with IgA glomerulonephritis were studied to reveal the incidence, composition and possible clinical significance of extraglomerular vascular immune deposits. IgA deposits were detected in 20 cases, IgM in 28 (in 5 together with IgA), C3 in 317 and no vascular deposits in 60 cases. C3 and IgA deposits were granular, resembling mesangial deposits, while IgM deposits were lumpy, similar to IgM deposits in sclerotic and hyalinized glomeruli. The incidence of vascular lesions in patients with IgA (30%) and C3 deposits (24%) was not significantly higher as compared to those without vascular deposits (20%), but was significantly higher in patients with IgM deposits (68%, P < 0.00004). Only the presence of vascular IgM deposits correlated significantly with severe glomerulosclerosis, arterial hypertension and elevated serum creatinine levels (all P < 0.001). We conclude that neither C3 nor IgA deposits, in spite of their suggested immune complex nature, contribute significantly to the development of vascular lesions. Lumpy IgM deposits, probably the result of insudation of plasma proteins into the blood vessel walls, were associated with advanced vascular lesions and glomerulosclerosis and are probably a part of non-immune mediated progression of IgA glomerulonephritis.