Production of interleukin-6 by human retinal pigment epithelium in vitro and its regulation by other cytokines.

Interleukin-6 (IL-6) is a pleiotropic cytokine which produces uveitis if administered intraocularly. It has been demonstrated in the aqueous of patients with various uveitis entities. We have investigated the ability of human retinal pigment epithelium (RPE) to produce IL-6 in vitro, both unstimulated, and in the presence of interleukin-1 (IL-1), tumor necrosis factor alpha (TNF), interferon (IFN) gamma, and lipopolysaccharide (LPS). Five human RPE cell lines were cultured over a 6-day period, both unstimulated and in the presence of these cyokines. IL-6 in the supernatants was measured using an ELISA assay. Unstimulated RPE produced small amounts of IL-6. IL-1 at 100 or 10 U/ml markedly upregulated IL-6 production, and TNF at 1000, 100 or 10 U/ml did so to a lesser extent. Neither IFN gamma or LPS alone increased IL-6 expression, but together gave significant upregulation. Thus human RPE can produce IL-6 and may be the source of this cytokine in ocular inflammatory states.