Interaction of aggregates of reduced insulin with gamma globulin and complement: a pathogenetic hypothesis

Renal biopsies performed on diabetics

Metabolic disorders and immunological factors are discussed in connection with the pathogenesis of diabetic microangiopathy. Renal biopsies were obtained from 22 diabetics (8 women aged 18 to 53, 14 men aged 15 to 52). 7 of the 22 patients had been suffering from diabetes for 2 weeks to 3 years, 10 for 7 to 25 years, 2 showed a pathological glucose-tolerance test, i.e., they had been "latent" diabetics, and 3 patients, had been so-called "potential" subjects of diabetes due to hereditary traits or delivery of big babies. They were examined by light miroscopy as well as by immunofluorescence microscopy. A number of cases were chosen for the differentiation and counting of glomerular cells (n=8) as well as for electron microscopic (n=7) and polarizing-microscopic (n=6) examinations. Histologically, focal proliferations of mesangial cells as well as an increase in mesangial substance in the glomeruli was found in all cases, although in a varying degree of intensity. These results were confirmed by both the glomuerular cell count and electron-microscopic examination. Immunofluorescence microscopy made it possible to detect frequently both IgA (9/17) and IgG (9/17), usually in either linear or mesangial arrangements whereas it was less frequently possible to detect IgM (1/17) and albumin (1/8) and impossible to detect beta1C in the glomerulus. Labeled insulin was detected five times in the glomerulus. Polarizing-microscopic measurements made in order to discover possible submicroscopic variations in the structure of GBM showed deviations in the average values of anisotropic indices from the controls in the group of long-term diabetics only. The pathogenesis of diabetic microangiopathy may be described as an inflow of immunoglobulins and serum proteins into the mesangium because of an alteration of the capillary endothelium, the mesangial cell being thus caused to overfunction, proliferate and produce an excess of mesangial matrix. In prolonged diabetes the mesangial cell, so far as its own metabolism is concerned, will finally be affected to the point where its power of synthesis is modified in the sense of an excess and/or faulty composition of GBM (glomerular basement membrane).