Early mesangiolysis and monocyte influx observed in diabetic glomerulosclerosis: relation to nodule formation.

: Lytic changes to the mesangium and subendothelial area in diabetic glomerulosclerosis were studied by electron microscopy with an emphasis on the mechanism of nodule formation. Renal biopsy specimens were obtained from 30 diabetics (11 males, 19 females; 27 NIDDM, 3 IDDM; mean age, 52.2 years) with renal involvement. Evaluations were made of the glomerular lesions, particularly the ultra-structural findings contributing to nodule formation, mainly by electron microscopy. Varying degrees of lytic change, such as a loose and edematous mesangial matrix, widening of the subendothelial space, followed by endothelial detachment, and destruction of anchor points, were observed in close association with progression of the diffuse lesions. Plasma proteins were found to infiltrate into the widened subendothelial space. Mesangial cells also protruded into the same space and encroached around the whole capillary wall. The interposed mesangial cells were occasionally separated from the basement membrane. Monocytes identified from their ultrastructure were frequently present noticed in the lytic areas, suggesting a reaction to lytic changes. These processes may occur repeatedly with direct expansion of the mesangial matrix, subsequently revealing a nodular appearance.