Endotoxin-induced uveitis. Kinetics and phenotype of the inflammatory cell infiltrate and the response of the resident tissue macrophages and dendritic cells in the iris and ciliary body.

PURPOSE

Footpad injection of bacterial lipopolysaccharide (LPS) causes pronounced anterior uveitis in susceptible species and strains. Recent studies using wholemount techniques have demonstrated the presence of rich networks of major histocompatibility complex (MHC) class II-positive dendritic cells (DC) and resident tissue macrophages in the iris and ciliary body. The aim of this investigation was to determine the immunophenotype and dynamics of the inflammatory cell infiltrate during LPS-induced anterior uveitis using the wholemount method and to examine the response of the resident tissue macrophages and DC to an acute inflammatory episode in the anterior segment.

METHODS

Female Lewis rats (8 to 12 weeks old, n = 49) received a single footpad injection of 100 micrograms of LPS and were killed at various times up to 6 weeks after injection. The iris-ciliary body complex from each eye was removed intact and subdivided into segments and immunostained using a panel of monoclonal antibodies to a variety of immune cell types.

RESULTS

The wholemount method clearly illustrates that during endotoxin-induced uveitis (EIU), the earliest cellular infiltrate includes small, round ED1+ mononuclear cells marginating in the iris vasculature approximately 2 hours after injection. Marginating Ox42+ polymorphonuclear leukocytes were detectable in the iris vessels approximately 4 to 6 hours after injection and were especially numerous in the ciliary body base approximately 24 hours after injection. The overall density of resident tissue macrophages (ED2+) remained largely unchanged in the course of EIU. In contrast, the total number of MHC class II-bearing (Ox6+) cells (putative dendritic cells) increased 30% in the first 6 hours and 200% by 72 hours. During the acute phase of the inflammatory response (up to 24 hours), the proportion of these cells with a dendritiform morphology decreased (93% to 50%). The number of T cells showed a biphasic response peaking at 4 to 6 hours and again at 24 hours (290 cells/mm2); however, their numbers had resumed normal low density (4 cells/mm2 to 25 cells/mm2) by 6 weeks.

CONCLUSIONS

The results suggest that the neutrophilic infiltration in EIU occurs predominantly in the base of the ciliary body, whereas the monocytic and lymphocytic infiltrate occurs in the iris vasculature. Resident tissue macrophages do not undergo marked changes in density or morphology in the early course of the disease. Recruitment of T cells into the anterior segment in EIU may suggest a previously unsuspected role for these cells in the immunopathology of this disease. Changes in density and morphology of MHC class II+ DC in the iris, which persisted for at least 6 weeks, were interpreted as an increase in recruitment and migration of these cells that may serve to enhance the efficiency of immune surveillance in the anterior segment at crucial times of bacterial infection.