Analysis of lymphocyte-endothelial interactions at the blood-retina barriers in vivo using scanning laser ophthalmoscopy
Lymphocyte-endothelial interactions play a central role in the progression of T-cell mediated autoimmune disease. In the eye the mechanisms by which lymphocytes adhere to the vascular endothelium and migrate to cause areas of retinal and choroidal inflammation are not completely understood. To understand these mechanisms a method was developed to track lymphocyte circulation in vivo. By combining the use of fluorescent dyes to label lymphocytes ex vivo and the scanning laser ophthalmoscope (SLO), the lymphocyte circulation in both the retinal and choroidal circulation was detected and quantified. In the normal retinal and choroidal circulation leukocyte velocity was found to be 10.4 (5.3)(SD) mm/s in the retinal arteries, 5.1 (2.5) in retinal veins mm/sec, 1.1 (1.2)mm/sec in retinal capillaries and 2.1 (2.1) mm/sec in the choroidal vessels. A relatively small fraction of circulating lymphocytes was found to adhere to the retinal capillaries and the choroid. In the retinal capillaries adhering cells were found to stop abruptly without prior rolling. The imaging method was applied to investigate an animal model of endogenous posterior uveitis, experimental autoimmune uveoretinitis (EAU). Increased lymphocyte adhesion to both the retinal capillary and choroidal circulations was detected before the onset of clinical inflammation in the posterior segment. The increased adhesion to the retinal capillaries appeared to be dependent on the activity of leukocyte-function antigen-1 (LFA-1) on lymphocytes. However, the increased lymphocyte adhesion to the choroid could not be reduced by initiation of LFA-1 activity.