Purpose: Ample evidence is available demonstrating that cytokines play a pivotal role in the pathogenesis of uveitis. Because little is known concerning the site of cytokine synthesis in the eye, cytokine mRNA expression was analyzed in the uvea, retina, and cornea during endotoxin-induced uveitis (EIU) in the rat.
Methods: RNA was isolated from the iris, ciliary body, choroid-sclera, retina, and cornea at different points in time after foot-pad injection of 200 micrograms lipopolysaccharide (LPS) in Lewis rats. Reverse-transcription polymerase chain reaction analysis was used to determine tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta), IL-6, IL-10, interferon gamma (IFN-gamma), monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 2 (MIP-2), and IL-1 receptor antagonist (IL-1RA) mRNA expression.
Results: Maximal mRNA expression of all cytokines examined already was observed in the uvea 4 hours after systemic LPS injection, before the onset of clinical uveitis. Elevated expression of TNF-alpha, IL-1 beta, IL-6, IFN-gamma, MCP-1, and MIP-2 was also observed concomitant with maximal uveitis, at 22 to 24 hours. Except for IL-10 and IFN-gamma, all cytokines investigated were induced in the retina, with maximal expression at 22 to 24 hours. Expression of IL-1RA was detected in the uvea and retina at 4 hours and remained elevated up to 48 hours, when the clinical uveitis started to decline. LPS did not induce cytokine expression in the cornea. Strikingly, a considerable expression of IL-1RA was found in normal corneas, suggesting an inherent control mechanism for IL-1-mediated responses.
Conclusions: Systemic LPS injection induces elevated mRNA expression of multiple cytokines and IL-1RA in the uvea and retina during various stages of EIU. This suggests that these mediators may contribute to the development and recovery of this intraocular inflammation.