Relationship of polymorphonuclear leukocytes to capillary dropout in the human diabetic choroid

Capillary dropout is an initial event in diabetic retinopathy, but the etiology is unknown. Recent evidence suggests that similar events may occur in the diabetic choroid. We have developed a method to evaluate the relationship between the polymorphonuclear leukocytes (PMNs) and capillary dropout in the human diabetic choroid using alkaline phosphatase (APase) histochemistry to label blood vessels and nonspecific esterase activity to identify PMNs. The number and distribution of PMNs in diabetic and nondiabetic choroidal capillaries (choriocapillaris) were analyzed in the flat perspective and the tissue then flat embedded in glycol methacrylate for histological sectioning. The total number of PMNs was increased within the choriocapillaris in five diabetic eyes (170.9 +/- 12.9 PMNs/mm2 of choroid) compared with five nondiabetic eyes (84.2 +/- 16.9 PMNs/mm2; P < 0.001). PMNs were almost always within blood vessel lumens and not in interstitial tissue. In the diabetic choroid, increased numbers of PMNs were present in areas of choriocapillaris with pathological changes (loss in APase activity and choroidal neovascularization) compared with nonpathological choriocapillaris (205.1 +/- 46.9 PMNs/mm2 in pathological versus 152.3 +/- 23.4 PMNs/mm2 in nonpathological areas; P < 0.001). PMNs were often queued up within the lumens of capillaries, demonstrating loss in APase activity. We have observed an increased number of PMNs in diabetic choroid compared with control nondiabetic choroids, and PMNs in diabetic choroid were associated with loss in APase activity, which was related to loss in viable endothelial cells. The results suggest that PMNs contribute to vaso-occlusive processes and endothelial cell injury in the diabetic choroid.