Immunopathology of renal extracellular membranes in diabetes mellitus. Specificity of tubular basement-membrane immunofluorescence.

This study documents the presence of marked immunofluorescence for IgG and albumin in renal extracellular membranes, especially tubular basement membranes (TBM), of patients with severe diabetic nephropathy. A comprehensive immunofluorescent analysis was carried out on kidney tissue from 83 patients--Group I: 24 living normal renal allograft donors and two infants less than one week of age. Group II: 24 patients with severe nephropathy who had juvenile onset of diabetes 16 to 30 years previously and who ranged in age from 20 to 47 years. Group III: 33 patients with severe kidney disease of varied etiologies with an age range of five to 63 years. The sections were assayed for a variety of proteins (immunoglobulins, complement components, and tissue antigens). Kidney sections of all patients with severe diabetic nephropathy were readily distinguished from kidneys of other patients and normals by the intense linear staining of the extracellular membranes, especially the tubular basement membrane for IgG and and albumin. Dual-labeled studies using FITC anti-basement membrane (BM) and tetramethyl rhodamine (TMR) antialbumin demonstrated localization of the albumin predominantly to the outer but also the inner TBM while the BM antisera reacted more intensely with the inner membrane. There is no evidence that an immunologic process is responsible for these findings. These immunofluorescent findings are specific for severe diabetic nephropathy and may reflect structural changes in the renal extracellular membranes that permit entrapment of serum proteins, possibly due to changes in permeability.