EXPRESSION OF INTERLEUKIN-1-ALPHA, INTERLEUKIN-1-BETA, AND AN INTERLEUKIN-1 RECEPTOR ANTAGONIST IN HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

mRNA expression and protein production of interleukin-1α, interleukin-1β and intracellular and secreted forms of an interleukin-1 receptor antagonist were measured in visually confluent monolayers of unstimulated cultured human retinal pigment epithelial cells and after cells were stimulated with recombinant cytokines. Using reverse transcription polymerase chain reaction, transcripts for interleukin-1α and interleukin-1β were not detected in unstimulated cells from any of six donors whereas mRNA expression for both interleukin-1α and interleukin-1β was readily induced in all six cell lines after cells were stimulated with recombinant IL-1 (α or β), tumor necrosis factor α, or lipopolysaccharide. The combination of cycloheximide and recombinant interleukin-1 caused a 14-fold enhancement of interleukin-1α and interleukin-1β mRNA expression above that observed after cells were stimulated with interleukin-1 alone. After stimulation by interleukin-1, cells produced intracellular interleukin-1α protein, but did not secrete it into medium. In contrast, interleukin-1β protein was not detected in cell lysates or conditioned-medium after stimulation with interleukin-1. An intracellular interleukin-1 receptor antagonist was expressed constitutively by human retinal pigment epithelial cells; mRNA transcripts were enhanced in a dose and time dependent manner after cells were exposed to recombinant interleukin-1 or tumor necrosis factor α. In contrast, mRNA for a secreted form of the interleukin-1 receptor antagonist was not detected under basal conditions or after cells were stimulated by recombinant cytokines. Interleukin-1 receptor antagonist protein was found primarily in cell lysates; little interleukin-1 receptor antagonist protein was secreted by the cells. The presence of cell-associated interleukin-1 receptor antagonist was confirmed by immunocytochemistry. Levels of cell-associated IL-1 receptor antagonist protein were not significantly influenced by recombinant interleukin-1 or tumor necrosis factor α. Endogenous expression of interleukin-1 receptor antagonist may attenuate the effect of exogenous or endogenous interleukin-1, thus providing the RPE cell a means of maintaining interleukin-1 homeostasis in ocular inflammatory disease. © 1992.