Interleukin-6 (IL-6) gene expression and secretion by cytokine-stimulated human retinal pigment epithelial cells

Abstract

Retinal and choroidal inflammatory lesions are important causes of visual loss, but the mechanisms regulating intraocular inflammation remain poorly understood. By virtue of its position at the blood-retina barrier, the retinal pigment epithelium (RPE) cells may be critical to the initiation and propagation of ocular inflammation. Previously we showed that cytokine-stimulated RPE cells produce interleukin-8, a well-defined chemotactic factor for neutrophils and lymphocytes. In this study, we found that human RPE cells stimulated by human recombinant interleukin-1-[beta] (rIL-1[beta]) or tumor necrosis factor-[alpha] (rTNF-[alpha]) produce interleukin-6 (IL-6). Using a plasmacytoma proliferation assay, significant levels of IL-6 were found in media of RPE cells stimulated with either rIL-1[beta] or rTNF-[alpha] for 4 hr. Progressive accumulation of IL-6 in media overlying stimulated RPE cells occurred over the subsequent 20 hr. IL-1[beta] was a significantly more potent stimulator of RPE IL-6 production than TNF-[alpha]. RPE IL-6 production in response to each of these cytokines was also dose-dependent over a range of 20 pg to 20 ng ml-1. Specific anti IL-6 antibody, but not control immunoglobulin, neutralized RPE-derived IL-6 activity in the plasmacytoma proliferation assays. RPE IL-6 mRNA levels were detectable 1 hr after cytokine stimulation, plateaued within 8 hr in 24-hr assays, and demonstrated dose-dependent kinetics in 6 hr assays. Lipopolysaccharide failed to induce RPE IL-6 mRNA expression or RPE IL-6 production. Our findings indicate that RPE cells express IL-6 mRNA and secrete biologically active IL-6 when stimulated by inflammatory cytokines. RPE IL-6 secretion may be important in ocular lesions involving differentiation and activation of lymphocytes.