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AIMS: Previous studies have implied that interferon gamma (IFN-gamma) is involved in the pathogenesis of endotoxin induced uveitis (EIU) in the rat. This study investigated the source of IFN-gamma in the iris during EIU.

METHODS: Whole mounts of iris were isolated from Lewis rats before and at different times (from 4 hours to 14 days) after foot pad injection of 200 micrograms Salmonella typhimurium lipopolysaccharide (LPS). Immunohistological analysis was performed using monoclonal antibodies (mAbs) specific to rat IFN-gamma (DB12 and DB13). mAbs specific to monocytes, macrophages, and dendritic cells and MHC class II were used to asses the inflammatory response in the eye (ED-1, ED-2, and OX-6). An antibody specific to neurofilaments (2H3) was used to stain nerve fibres in the normal iris.

RESULTS: LPS administration induced acute intraocular inflammation, characterised by a massive infiltration of monocytes/macrophages and increased numbers of MHC class II positive cells in the iris. IFN-gamma immunoreactive cells were not detected in iris whole mounts of control rats. Strikingly, IFN-gamma immunoreactivity was found in fibres from 4 hours until 10 days after LPS injection, with the most intense staining at 48-72 hours. Other DB12 or DB13 positive cells were not detected in the iris. The pattern of DB12 and DB13 staining in the inflamed iris was similar to the 2H3 staining of neurons in the iris of control rats.

CONCLUSION: These results show that systemic LPS administration induces IFN-gamma immunoreactivity in iris fibres and suggest that iris nerve fibres may be a source of IFN-gamma during EIU. The IFN-gamma immunoreactive material in the iris nerve fibres may be identical to neuronal IFN-gamma.