Expression of macrophage migration inhibitory factor in corneal wound healing in rats.

PURPOSE The study was conducted to evaluate the expression of macrophage migration inhibitory factor (MIF) during penetrating corneal injury. METHOD A penetrating linear incision (2 mm) was made in the center of the right cornea with a razor blade. The expression of MIF in the lacerated eye and in the contralateral eye was examined by immunohistochemistry at 3, 6, 24, 48, and 72 hours after injury. Concentrations of MIF in the aqueous humor of the injured and contralateral eyes were also measured by enzyme-linked immunosorbent assay. The expression of MIF messenger RNA (mRNA) in the injured cornea was quantified by reverse transcription-polymerase chain reaction and subsequent Southern blot analysis. RESULTS Positive migration inhibitory factor staining was observed in the basal cells of epithelial and endothelial cells of the normal rat cornea. The positive staining of the central corneal epithelium diminished at 3 hours after injury. At 6 hours after injury, positive MIF staining reappeared on the basal cells of the injured area, whereas the staining of the contralateral eye remained unchanged. Enzyme-linked immunosorbent assay of the aqueous humor revealed that the MIF concentration was elevated in both the injured and the contralateral eyes. The maximum concentration of aqueous MIF was observed at 6 hours after injury in both eyes. Reverse transcription-polymerase chain reaction and Southern blot analysis revealed that MIF-mRNA expression in the injured cornea increased from 6 to 48 hours after injury. CONCLUSION The results of immunohistochemistry suggest the possibility that MIF is released from the corneal epithelial cells of the injured eye within 3 hours. Conversely, the MIF-mRNA level of the injured cornea is increased from 6 to 48 hours after injury and then diminished. In addition, unilateral corneal injury induces bilateral upregulation of MIF in the aqueous humor.