Evaluation of fluorescein-labeled autologous leukocytes for examination ofretinal circulation in humans

Purpose. Increased leukocyte-endothelium interaction have been suggested as a phenomenon contributing to capillary occlusion and/or rupture of the blo od-retina barrier during human retinal vascular diseases. This study was pe rformed to evaluate if fluorescein-labeled autologous leukocytes (FLALs) ca n be used for examination of leukocyte transit in the human retina. Methods. The preparation consisted of human dextran-separated leukocytes mi xed with fluorescein. After reinjection in normal subjects and in one diabe tic patient, a confocal scanning laser ophthalmoscope was used to visualize them in the retinal circulation. The changes between FLALs and control leu kocytes in the expression of leukocytes adhesion molecules CD11b and CD62L were evaluated by flow cytometry. Results. The circulating FLALs were clearly visible in retinal vessels. The mean (+/- SD) capillaries velocity was 1.43 (+/- 1.3) mm/s in the macula a nd 1.82 (+/- 1.4) mm/s in the peripapillary area. No leukostasis was detect ed in the normal subjects, while it was detected in te diabetic patient. Fl ow cytometry revealed an increase in CD11b and a decrease in CD62L expressi on of leukocytes after labeling, suggesting that compared to normal leukocy tes FLALs are more susceptible to interact with vascular endothelium. Conclusions. The use of FLAL is presently the only technique applicable in humans for study of leukocyte transit in the retina. Their preparation is t echnically simple and unexpensive. Precise measurement of the velocity of l eukocytes in small vessels can be obtained. Despite evidence of a certain d egree of leukocyte activation after the labeling procedure, no leukostasis was detected in vivo in normal subjects. Potential applications for this te chnique may include the detection of leukostasis in the human retina during severe forms of diabetes and retinal phlebitis.