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) cause s pronounced anterior uveitis in susceptible species and strains, Rece nt studies using wholemount techniques have demonstrated the presence of rich networks of major histocompatibility complex (MHC) class II-po sitive dendritic cells (DC) and resident tissue macrophages in the iri s and ciliary body. The aim of this investigation was to determine the immunophenotype and dynamics of the inflammatory cell infiltrate duri ng LPS-induced anterior uveitis using the wholemount method and to exa mine the response of the resident tissue macrophages and DC to an acut e inflammatory episode in the anterior segment. Methods. Female Lewis rats (8 to 12 weeks old, n = 49) received a single footpad injection o f 100 mu g of LPS and were killed at various times up to 6 weeks after injection. The iris-ciliary body complex from each eye was removed in tact and subdivided into segments and immunostained using a panel of m onoclonal antibodies to a variety of immune cell types. Results. The w holemount method clearly illustrates that during endotoxin-induced uve itis (EIU), the earliest cellular infiltrate includes small, round ED1 (+) mononuclear cells marginating in the iris vasculature approximatel y 2 hours after injection. Marginating Ox42(+) polymor-phonuclear leuk ocytes 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 residen t 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 respo nse (up to 24 hours), the proportion of these cells with a dendritifor m morphology decreased (93% to 50%). The number of T cells showed a bi phasic response peaking at 4 to 6 hours and again at 24 hours (290 cel ls/mm(2)); however, their numbers had resumed normal low density (4 ce lls/mm(2) to 25 cells/mm(2)) by 6 weeks. Conclusions. The results sugg est that the neutrophilic infiltration in EIU occurs predominantly in the base of the ciliary body, whereas the monocytic and lymphocytic in filtrate occurs in the iris vasculature. Resident tissue macrophages d o not undergo marked changes in density or morphology in the early cou rse of the disease. Recruitment of T cells into the anterior segment i n 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, w ere interpreted as an increase in recruitment and migration of these c ells that may serve to enhance the efficiency of immune surveillance i n the anterior segment at crucial times of bacterial infection.