Synergistic Effect of TNF-α and Either IL-4 or IL-13 on VCAM-1 Expression by Cultured Human Corneal Fibroblasts

Abstract

To examine the role of corneal fibroblasts in the pathogenesis of vernal keratoconjunctivitis, we investigated the effects of tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-13 on the expression of vascular cell adhesion molecule (VCAM)-1 by cultured human corneal fibroblasts. Cultured human corneal fibroblasts were incubated with various combinations and concentrations of TNF-alpha, IL-4, and IL-13. The cell surface expression of VCAM-1 was subsequently evaluated by whole-cell enzyme-linked immunosorbent assay and immunocytochemistry, and the abundance of VCAM-1 mRNA in cell lysates was determined by quantitative reverse transcription and polymerase chain reaction analysis. Corneal fibroblasts incubated in the absence of cytokines exhibited minimal expression of VCAM-1. Whereas incubation of the cells with TNF-alpha, IL-4, or IL-13 alone, or with the combination of IL-4 and IL-13, induced only a small increase in VCAM-1 expression, exposure of the cells to TNF-alpha in combination with either IL-4 or IL-13 resulted in a marked synergistic increase in expression of this adhesion molecule that was both time and dose dependent. The abundance of VCAM-1 mRNA in corneal fibroblasts was also increased in a synergistic manner by incubation of the cells with TNF-alpha together with either IL-4 or IL-13. Stimulation of human corneal fibroblasts with the combination of TNF-alpha and either IL-4 or IL-13 resulted in synergistic increases in both the abundance of VCAM-1 mRNA and the cell surface expression of VCAM-1 protein. This cytokine-induced increase in VCAM-1 expression by corneal fibroblasts may contribute to eosinophil infiltration in corneal lesions associated with vernal keratoconjunctivitis.