Resident and infiltrating immune cells in the uveal tract in experimental autoimmune uveoretinitis

Purpose: To investigate the dynamics of resident and infiltrating immune cells in the choroid and iris during the early and late stages of experimental autoimmune uveitis (EAU). Methods: EAU was induced in Lewis rats by footpad immunisation with crude retinal extract and complete Freund's adjuvant with concurrent intraperitoneal injection of Bordetella pertussis. Five experimental and five control animals (adjuvant alone) were studied at each of days 5, 7, 9, 11 and 42. Further controls included 5 normal rats and five injected with pertussis alone. Immunohistochemical localisation of resident macrophages (ED2), MHC class II (OX6)⁺ dendritic cells (DC), infiltrating mononuclear cells (ED1) and T cells (OX19/R73) was performed on choroidal and iris wholemounts. Results: No marked qualitative and quantitative changes were observed in the density and appearance of ED2⁺ cells in the choroid and iris prior to disease onset. On day 11, infiltration of ED1⁺ cells had occurred in the iris but not the choroid, the total density of OX6⁺ cells was elevated in the choroid (1152 ± 192 cells/mm²⁾), however, infiltration of T cells was evident in both choroid (286 ± 161 cells/mm²) and iris (196 ± 72 cells/mm²). The density of T cells and Ia⁺ DC remained elevated in the choroid and iris in the late stages of EAU. Conclusions. The mononuclear infiltrate in EAU first appears in the anterior uveal tract. The increased density of Ia⁺ cells in the iris and choroid on day 11 may represent increased trafficking of DC in the eye during uveoretinitis. Furthermore, the increased density of Ia⁺ DC and macrophages concurrent with the influx of autoreactive T cells suggests these cells may be acting locally as antigen presenting cells in EAU.