Trauma and alkali burns induce distinct patterns of cytokine gene expression in the rat cornea

Cytokines such as the interleukins (IL) and tumor necrosis factor alpha (TNFα) have traditionally been associated with paracrine regulation of immune reactions. These proteins also have properties suggestive of functional roles in the inflammatory and reparative responses to tissue injury. In this study, mRNA levels for IL-1α, IL-1β, IL-6, TNFα, interferon γ, transforming growth factor B₁ and CD₄ were monitored in rat corneas at times from 1 hour through 2 weeks after incisional trauma of alkali burns. Transcripts for IL-1α, TNFα, and TGFβ₁, were present in most corneal samples; whereas those for IFNγ and CD₄ were not detected. As early as 1 hour following either of these non-immunologic forms of injury, expression of IL-6 mRNA levels was induced. Only in corneas with alkali burns did IL-6 induction persist from days 1 through 7. The alkali-injured corneas also had markedly increased IL-1β mRNA levels from days 1 through 7. These observations indicate that cytokine mRNA is induced in the cornea by trauma without an apparent immunologic stimulus. Our data are consistent with the hypothesis that corneal tissues respond to different types of injury with different patterns of cytokine gene expression.