THE BEHAVIOR OF ED1-POSITIVE AND ED2-POSITIVE CELLS IN THE RAT IRIS AND CHOROID FOLLOWING PENETRATING KERATOPLASTY AND CYCLOSPORINE-A THERAPY

Background: The presence, morphology and distribution of ED1 and ED2cells have been recently reported in detail in the uveal tissues of th e rat. These cells, particularly those of dendritic morphology, are po ssibly capable of antigen presentation and, therefore, may play an imp ortant role in immune processes of uveal and other ocular tissues. Usi ng the whole-mount technique, the distribution of ED1+ and ED2+ cells in the rat iris and choroid was investigated following penetrating ker atoplasty (PKP) and following treatment with cyclosporin A (CsA). Meth ods: Lewis (LW) rats received corneal buttons from Lewis-Brown Norway (LW-BN) donors and were randomly assigned to one of two groups: (I) op erated, untreated (n=24); (II) operated, CsA treated (10 mg/kg i.m.; n =22). Four groups served as controls: normal LW rats (n=13); (IV) unop erated, CsA treated (16 days' treatment; n=8); (V) eight corneal sutur es only, representing a simulated or ''sham'' operation (n=4); (VI) sy ngeneic operated (LW to LW; n=4). Animals of groups I and II were kill ed on the 5th, 9th and 13th postoperative days and on appearance of th e corneal rejection (group I, day 13; Group II, day 16). Both eyes wer e enucleated, immediately fixed, and iris-choroid flat mounts were exa mined for ED if and ED2+ cells using APAAP immunohistochemistry. Resul ts: In the normal LW rat iris, ED1+ and ED2+ cells of both non-dendrit ic and dendritic morphology were observed. The placement of sutures in the cornea and PKP with or without treatment resulted in a reasonably regular response in both the iris and the choroid in the operated and partner eye. These included: (a) an increase in round iridal ED1+ and ED2+ cells in the operated eye and in round ED1+ cells in the partner eye; (b) a decrease in dendritiform ED2+ cells in the iris of the ope rated eyes as well as in the partner eye; and (c) a decrease in the de ndritiform ED2+ cells in the choroid of the operated and partner eye. CsA treatment alone in unoperated animals resulted in significant decr eases in the number of dendritiform ED1+ cells in the iris and in the dendritiform ED2+ cells in the choroid. Conclusion: Corneal transplant ation in the Lewis rat results in responses in ED1+ and ED2+ cells in uveal tissues in both the operated eye as well as in the partner eye. The differences in cell behaviour supports the idea that distinct immu ne-competent cell populations are present within uveal tissues and tha t they may have differing roles in the pathological eye.