Glial cell involvement in vascular occlusion of diabetic retinopathy.

Twenty areas of retinal vascular occlusion from ten eyes of 6 diabetic patients were studied by immunohistochemistry to type IV collagen (basement membranes), von Willebrand factor (endothelial cells), and to glial fibrillary acid protein (glial cells) on serial sections. In all studied lesions immunoreactivity to type IV collagen and von Willebrand factor was confined to the retinal vascular walls whereas the material accumulated to occlude the vascular lumens centrally displayed immunoreactivity to glial fibrillary acid protein. All arterioles observed in the lesions were occluded. These arterioles had retained their circular shape, and the intravascular glial protein immunoreactivity communicated with the extravascular glial tissue through localised breaks in the vascular wall. The intravascular immunoreactivity was found to continue inside the arteriole along its successive diminishing to reach the capillary level. The venules were only occluded in less than half of the studied lesions. These venules were collapsed to assume a bean-like shape, and sequences with total obliteration of the vascular lumen alternated with sequences where a residual space corresponding to the former lumen displayed immunoreactivity to glial protein. The paper suggests that glial cell invasion, but not endothelial cells or basement membrane thickening, occludes the vascular lumen in areas of retinal non-perfusion secondary to diabetic retinopathy.