THE ORDERED ARRAY OF PERIVASCULAR MACROPHAGES IS DISRUPTED BY IL-1-INDUCED INFLAMMATION IN THE RABBIT RETINA

In this study we have shown that an antibody to CD18 identified a popu lation of cells in the rabbit retina that resembled the perivascular m acrophage found in other regions of the central nervous system. In the normal retina these cells possessed a ramified morphology and present ed in an ordered array on the vitreal surface in association with the epiretinal vessels. Approximately 50% of the perivascular macrophages constitutively expressed MHC class II. In response to interleukin-1 be ta (IL-1 beta)-induced inflammation, these cells became activated, as evidenced by a change from a ramified to an ameboid morphology and inc reased expression of MHC class II, and migrated away from the vessels. These changes were first detected around 3 h post-intraocular challen ge coincident with the onset of inflammation. At the peak of the infla mmatory response (similar to 24 h post-challenge), many activated peri vascular macrophages were no longer associated with the vessels and fo rmed long ''cords'' of MHC class II+ cells associated with underlying deposits of fibrin. In eyes challenged with heat-inactivated IL-1, no change in the morphology or distribution of the perivascular macrophag e was noted. At 3 weeks post-challenge with IL-1, the number and distr ibution of the perivascular macrophages were restored to baseline valu es, although with a reduced cell size. Since these changes closely res emble those that occur in non-lymphoid dendritic cells in the skin, he art, and/or kidney following activation with cytokines or bacterial pr oducts, the results suggest that the perivascular macrophage represent s the dendritic cell of the retina and may thus play an important role in immune surveillance in the eye and maintenance of the blood-retina barrier. (C) 1996 Wiley-Liss, Inc.