Synthesis of Ip–10, I–Tac, and Mig, the Three Elr– A–Chemokines, Are Differentially Regulated in Human Corneal Epithelial Cells

Abstract

Abstract: : Purpose:CD4+ T lymphocytes are important mediators of inflammation in the infected cornea. However, the chemokines responsible for recruiting CD4+ T–lymphocytes into the inflamed cornea have not been clearly defined. The three ELR^– chemokines, IP–10, MIG, and I–TAC, are CD4+ T–cell recruiting chemokines. The purpose of this study was to determine if these three chemokines can be expressed in human corneal epithelial cells (HCEC) in response to proinflammatory mediators. Methods:Cultures of HCEC were stimulated with combinations of human recombinant interleukin–1α (IL–1α), tumor necrosis factor–α (TNF–α), or interferon–γ (IFN–γ). At selected times post–stimulation, culture supernatants were collected and assayed for IP–10, MIG, and ITAC by ELISA. Results: Stimulation of HCEC with the two inducers (IL–1α or TNF–α) increased IP–10 protein synthesis >500–fold higher while stimulating insignificant levels of MIG and I–TAC (p–value >0.05). In contrast, stimulation of cells with IFN–γ enhanced synthesis of all three ELR^– chemokine >350–fold. HCEC stimulated with combinations of TNF–α or IL–1α and IFN–γ secreted >100 ng of IP–10 and >7.5 ng of I–TAC. These levels were >150–fold higher than that produced when HCEC were exposed to only TNF–α, IL–1α, or IFN–γ. In contrast, MIG protein synthesis was not enhanced in response to stimulation with cytokine combinations. Conclusions: IP–10 protein synthesis can be up–regulated in HCEC by TNF–α, IL–1α, and IFN–γ stimulation. In contrast, I–TAC and MIG can only be upregulated in response to IFN–γ stimulation. Furthermore, combinations of TNF–α or IL–1α and IFN–γ synergistically interacted to induce an increase in IP–10 and I–TAC protein levels without enhancing MIG protein synthesis. These results suggest that even though synthesis of all three ELR^– chemokines is upregulated in HCEC by cytokines found in inflamed corneas, expression of each chemokine gene is differentially regulated with MIG synthesis being the most stringently controlled and IP–10 synthesis the least controlled.

Keywords: cornea: epithelium • inflammation • cytokines/chemokines