Synthesis of type II interleukin-1 receptors by human corneal epithelial cells but not by keratocytes

PURPOSE. The purpose of this study was to determine whether human corneal epithelial cells and keratocytes synthesize both the soluble and membrane forms of the type II IL-1 receptor (IL-1RII). METHODS. Primary cell cultures of human corneal epithelial cells and keratocytes were established from human corneas. RT-PCR was used to analyze cell cultures for expression of IL-1RII mRNA. The capacity of corneal cells to synthesize membrane-bound IL-1RII was determined by immunofluorescence microscopy, whereas ELISA was used to quantitate synthesis of soluble IL-1RII after IL-1alpha and TNF-alpha stimulation. RESULTS. Corneal epithelial cells expressed IL-1RII mRNA. The cells also stained positive for membrane-bound IL-1RII, and media harvested from epithelial cell cultures contained up to 50 pg/ml of soluble IL-1RII. Both IL-1alpha and TNF-alpha significantly enhanced the amounts of soluble IL-1RII released from epithelial cell surfaces. In contrast to epithelial cells, corneal keratocytes did not express IL-1RII mRNA. Membrane-bound IL-1RII was not detected on keratocytes, nor was soluble IL-1RII detected in culture media harvested from these cells. CONCLUSIONS. Human corneal epithelial cells but not corneal keratocytes synthesize both membrane and soluble forms of IL-1RII. Because both forms of IL-1RII can function as IL-1alpha antagonists, the results suggest that human corneal epithelial cells but not corneal keratocytes have evolved the capacity to dampen IL-1alpha responses through the production of IL-1RII.