Retinal leukocyte behavior in experimental autoimmune uveoretinitis of rats

In vivo retinal leukocyte behavior in the experimental autoimmune uveoretinitis (EAU) of rats was investigated using acridine orange digital fluorography. The technique employed high resolution images obtained from a scanning laser ophthalmoscope (SLO) subsequent to staining with the fluorescent nuclear dye, acridine orange. Two weeks after immunization with synthetic peptides of retinal soluble antigen (S-Ag), acridine orange was intravenously injected, and fundus images were generated by SLO. Many rolling leukocytes were observed along the venous walls as slowly moving fluorescent dots; moreover, leukocytes infiltrating into the vitreous cavity were also noted especially over the retinal veins, but not over the retinal arteries. In addition, major retinal vessels were significantly dilated. The diameters of the retinal veins at a distance of 1 disc diameter away from the center of the optic disc were 49.8+/-4.5 micron for the normal rats and 88.2+/-3.6 micron for the EAU rats, respectively (P<0.001). Similarly, the diameters of retinal arteries were 32.6+/-3.7 micron for the normal rats, 53.8+/-1.5 micron for the EAU rats, respectively (P<0.01). The dilation was more prominent in the veins than in the arteries. These results suggest that it is possible to visualize the retinal involvement of EAU in vivo. The results also suggest that leukocyte-endothelial interaction and extravascular infiltration in the retinal venous vasculature may play significant roles in the early stages of posterior segment inflammation in EAU.