Apoptosis is a prominent feature of acute anterior uveitis in the Fischer 344 rat

Aims-To examine the hypothesis that apoptosis of infiltrating cells contrib utes to spontaneous resolution of uveitis in clinically relevant rodent mod els. Methods-Experimental melanin induced uveitis (EMIU) was induced in Fischer 344 rats by immunisation with 250 mu g bovine ocular melanin. Endotoxin ind uced uveitis (EIU) was induced by injection of 200 mu g Escherichia coli li popolysaccharide. Formalin fixed, paraffin embedded ocular cross sections w ere stained by terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate biotin nick end labelling (TUNEL) to identify apoptotic cells. Indirect immunoperoxidase staining of paraformaldehyde lysine periodate fi xed tissue cross sections was used to demonstrate expression of inducible n itric oxide synthase (iNOS). Results-TUNEL positive mononuclear cells were observed in the anterior uvea during both EMIU and EIU at all selected time points. However, whereas the majority of mononuclear cells appeared apoptotic from the outset of diseas e, neutrophils were notably TUNEL negative at all time points examined. Man y infiltrating neutrophils expressed iNOS. Conclusion-Apoptosis occurs early in the course of rat EMIU and EIU, and ma y contribute to resolution of these diseases. In general, infiltrating mono nuclear cells die rapidly, while neutrophils survive, producing inducible n itric oxide synthase which may contribute to disease pathogenesis.