The Effects of Intraocular Injection of Interleukin-13 on Endotoxin-Induced Uveitis in Rats

Interleukin (IL)-13 is a strong immunomodulatory cytokine that inhibits macrophages from secreting proinflammatory mediators. This study was conducted to investigate the effect of intraocular injection of IL-13 on the development of endotoxin-induced uveitis (EIU) in the Lewis rat. One injection into the anterior chamber of recombinant human IL-13 (6 ng in 10 microl saline) was performed either simultaneously with a single injection of lipopolysaccharide (LPS) from Salmonella typhimurium into the footpad or 6 hours before the IL-13 injection. EIU was evaluated by slit lamp examination at 6, 16, and 24 hours after LPS injection. Counts of inflammatory cells were performed on cryostat sections after specific immunostaining. Anterior chamber paracentesis was performed, and kinetic analysis of the IL-13 injected in the anterior chamber was performed by ELISA. Cytokine and chemokine gene expression in the iris-ciliary body and the retina was evaluated by reverse transcription-polymerase chain reaction. A significant inhibition of ocular inflammation was observed in IL-13-treated rats at 16 and 24 hours after LPS injection. Unilateral injection of IL-13 inhibited EIU only in the injected eye. High levels of IL-13 were detected in the aqueous humor at 2 hours after local IL-13 injection to remain high up to 18 hours. In contrast, IL-13 was not detected in the corresponding sera. Quantitative analysis of inflammatory cells in ocular tissues showed a significant decrease in OX-42(+) cells (microglia, activated macrophages, dendritic cells, and polymorphonuclear leukocytes) and ED1(+) cells (monocytes-macrophages and dendritic cells) in treated rats. A decreased expression of TNF-alpha, IL-1 beta, IL-6, monocyte chemoattractant protein (MCP)-1, and macrophage inflammatory protein (MIP)-2 mRNAs was observed in the iris-ciliary body and the retina from IL-13-treated rats, whereas IFN-gamma was upregulated in the iris-ciliary body. Injection of IL-13 into the anterior chamber may inhibit the ocular inflammation induced by LPS injection by reducing intraocular cytokine and chemokine mRNA expression in ocular tissues.