Immunohistopathology of Diabetic Glomerulosclerosis

The cause and nature of the lesions in small blood vessels in diabetes mellitus is still unknown. Immunological mechanisms possibly related to reactions between insulin and antibodies to insulin, or damage caused by transudation of serum proteins, have been proposed by several investigators. To study these factors, we have examined by immunofluorescence thirty-seven samples of diabetic kidney tissue, showing varying degrees of pathology from normal to end-stage. A thin linear staining of the glomerular basement membrane was seen in about half the cases for IgG and IgM, including four tissues with normal or only slightly abnormal histology, and less frequently for fibrin, β₁C, albumin and ceruloplasmin. Heterologous complement did not bind in vitro to the basement membrane. Eluted IgG from the isolated glomeruli and sera from anephric diabetic patients did not react with normal glomeruli in indirect immunofluorescence. Fluorescent insulin did not bind to diabetic basement membrane and antibodies to insulin did so only exceptionally. The results are interpreted as showing that the serum proteins are found in the basement membrane as a result of nonimmunological mechanisms, possibly as a result of alteration in the glomerular basement membrane or mesan-gial dysfunction.