Synergistic induction of eotaxin expression in human keratocytes by TNF-alpha and IL-4 or IL-13.

PURPOSE To investigate the effects of tumor necrosis factor (TNF)-alpha, interleukin (IL)4, and IL-13 on expression of the chemokine eotaxin by cultured human keratocytes. METHODS Cultured human keratocytes were incubated with various combinations and concentrations of TNF-alpha, IL-4, and IL-13. The concentration of eotaxin in the culture supernatant was subsequently measured by enzyme-linked immunosorbent assay, and the amount of eotaxin mRNA in cell lysates was determined by reverse transcription-polymerase chain reaction analysis. RESULTS Keratocytes incubated in the absence of cytokines did not release detectable amounts of eotaxin into the culture medium. Whereas incubation of keratocytes with TNF-alpha, IL-4, or IL-13 alone or with the combination of IL-4 and IL-13 had only a small effect on eotaxin release, exposure of the cells to TNF-alpha in combination with either IL-4 or IL-13 resulted in a marked increase in eotaxin production that was both time and dose dependent. The abundance of eotaxin mRNA in keratocytes was also increased in a synergistic manner by incubation of cells with TNF-alpha together with either IL-4 or IL-13. CONCLUSIONS Stimulation of human keratocytes with the combination of TNF-alpha and either IL-4 or IL-13 resulted in synergistic increases in both the abundance of eotaxin mRNA and the release of eotaxin protein. This cytokine-induced increase in eotaxin production by keratocytes may contribute to eosinophil infiltration in inflammatory ocular diseases such as vernal keratoconjunctivitis.