Electron microscopy of experimental uveitis.

The fine structural features of the early pathological changes induced in uveal tissue by single intravitreal injections of three different quantities of bovine serum albumin (BSA) in rabbits toere studied. Small quantities of antigen (BSA) did not produce clinical signs of uveitis but a mild leukocytic infiltration (mainly monocytes) was found in the base of the ciliary body. The occasional basophilic leukocytes in the reaction site and choroidal mast cells were not degramdated and no alteration in the blood-aqueous barrier was found. Larger quantities of BSA produced mild uveitis and an impressive mononuclear infiltration in the base of the ciliary body, the root of the iris, the pars plana, and the peripheral choroid. The infiltrating cells included some which appeared to be intermediate between small lymphocytes and plasma cells, as tuell as monocytes. Inter cytoplasmic connections between monocytes and lymphocytes were observed, suggesting that immunological information was transferred by this means. Emigration of all types of mononuclear cells from blood vessels, and their passage through the ciliary epithelium into the posterior chamber, was frequently noted; however, in these regions, little alteration was observed in the structures associated with the blood-aqueous barrier. Small lymphocytes passed through, and larger mononuclear cells between, the endothelial cells when leaving the vascular system. Small islands of polymorphonuclear (PMN) heterophilic leukocytes were also seen in both the iridial and ciliary processes. In these regions, pronounced alteration was found in the blood-aqueous barrier and both basophilic leukocytes and mast cells showed degranulation. Injection of a still larger amount of BSA provoked severe uveitis with massive PMN heterophilic infiltration in the base of the ciliary body and in localized areas in the iridial and ciliary processes. Significant hemorrhage, thromboses, and necrosis of blood vessels xoere observed in the ciliary body. The structures associated with the bloodaqueous barrier showed marked changes. In addition to such vascular alterations, mononuclear cell infiltration teas seen in the pars plana and. the peripheral choroid.