DIFFERENTIAL REGULATION OF GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR GENE-EXPRESSION IN HUMAN CORNEAL CELLS BY PRO-INFLAMMATORY CYTOKINES

Neutrophils and Langerhans cells participate in inflammatory reactions within the human cornea. Because granulocyte-macrophage (GM)-CSF is a chemotactic and activating factor for these two cell types, we invest igated whether this cytokine is produced by human corneal epithelial c ells and corneal fibroblasts. Cultures of each cell type were exposed to increasing concentrations of IL-1 alpha or TNF-alpha. Culture super natants were assayed for GM-CSF by using ELISA and cytokine mRNA level s were monitored by using reverse transcriptase-PCR. IL-1 alpha treatm ent of both cell types resulted in the appearance of GM-CSF mRNA and t he production of >480 pg protein/10(6) cells. However, TNF-alpha treat ment yielded divergent results. Stimulation of epithelial cells with T NF-alpha resulted in the appearance of >560 GM-CSF mRNA molecules per cell and production of >1300 pg GM-CSF/10(6) cells. In contrast, stimu lation of corneal fibroblasts resulted in <16 GM-CSF mRNA molecules/ce ll and <60 pg GM-CSF/ 10(6) cells. Binding studies with I-125-labeled TNF-alpha revealed that corneal fibroblasts had as many receptor sites as did corneal epithelial cells. Furthermore, corneal fibroblasts cou ld respond to TNF-alpha-receptor-mediated signal transduction because they produced nanogram amounts of IL-6 after being treated with this c ytokine. The results suggest that both cell types synthesize GM-CSF in response to IL-1 alpha, but that only corneal epithelial cells produc e significant amounts of GM-CSF after TNF-alpha exposure. Differences in the responses of the two cell types to TNF-alpha may reflect a mean s of limiting accumulation of neutrophils and Langerhans cells and, th us, minimize corneal damage.