Abnormal binding of negatively charged serum proteins to diabetic basement membranes is largely a systemic phenomenon.

Direct immunofluorescence employing goat anti-human IgG, IgA, IgM, C3 component of complement, fibrinogen, albumin, and polyvalent immunoglobulins was performed on postmortem samples of gingiva, parotid gland, thyroid, kidney, and pancreas tissue of 15 diabetic and 15 control patients. Basement membrane thickness quantification of kidney tubules, gingival capillaries, and parotid gland ducts and acini was also done utilizing a calibrated magnifier on uniformly enlarged photomicrographs which had been specially stained to highlight basement membranes. Results revealed binding of IgG, albumin, and polyvalent immunoglobulin to kidney glomerular and tubular basement membranes and parotid ductal and acinar basement membranes in all diabetic subjects. Thyroid follicular basement membranes were positive in 8 of 15 diabetic patients for the same antisera. All gingival and pancreatic tissue from diabetic and control patients was negative for binding of all serum proteins tested. Basement membrane thickening in kidney tubules and gingival capillaries was observed in diabetic subjects; however, there was no apparent difference between diabetic and control patients in thickness of ductal or acinar basement membranes of the parotid gland.