title: Rabbit pigmented ciliary epithelium produces interleukin-6 in response to inflammatory cytokines.
abstract: Interleukin-6 is a multifunctional cytokine that is found in high concentrations in intraocular fluids during the uveitic response. Although monocytic cells are a major source of interleukin-6, resident intraocular cells may also contribute to its accumulation in intraocular fluids during uveitis. The purpose of this study was to determine whether interleukin-6 is produced by pigmented ciliary epithelial cells and whether agents known to stimulate interleukin-6 production, such as interleukin-1beta, tumor necrosis factor-alpha, bacterial endotoxin, and stimulators of the adenylyl cyclase/adenosine 3',5'-cyclic monophosphate system, increase interleukin-6 production by these cells. Primary and first-passage cultures of nontransformed rabbit pigmented ciliary epithelial cells were incubated with the test agents for varying periods of time in serum-free medium and interleukin-6 levels in the cell-conditioned medium were measured by bioassay.Little, if any interleukin-6 was released from pigmented ciliary epithelial cells incubated for up to 18 hr in serum-free medium. Interleukin-1betastimulated interleukin-6 release in a time- and concentration-dependent manner. Tumor necrosis factor-alpha, although ineffective alone, increased interleukin-1beta-induced interleukin-6 release in a concentration-dependent manner when co-incubated with interleukin-1betafor 18 hr. However, tumor necrosis factor-alphadid not enhance interleukin-1beta-induced interleukin-6 release if co-incubated with interleukin-1betafor a shorter time (6 hr). A 6 hr exposure to bacterial endotoxin did not stimulate interleukin-6 release from pigmented ciliary epithelial cells. Co-incubation of pigmented ciliary epithelial cells with interleukin-1betaand agents that stimulate the adenyl cyclase/adenosine 3',5'-cyclic monophosphate system through cell surface G-protein transduced receptors, i.e. isoproterenol, vasoactive intestinal peptide or prostaglandin E(2), significantly enhanced the ability of interleukin-1betato stimulate interleukin-6 release. However, neither the adenyl cyclase activator, forskolin or the adenosine 3', 5'-cyclic monophosphate-mimetic, dibutyryl 3',5'-cyclic monophosphate enhanced interleukin-1beta-induced release of interleukin-6. These results indicate that the pigmented ciliary epithelium is one potential source of interleukin-6 and may contribute to the elevation in intraocular fluid interleukin-6 levels observed during various intraocular inflammatory episodes. Although agents that activate the adenyl cyclase/adenosine 3', 5'-cyclic monophosphate system through cell surface G-protein transduced receptors increased interleukin-1beta-induced release of interleukin-6, the ineffectiveness of forskolin and dibutryl 3', 5'-cyclic monophosphate suggest that simply increasing intracellular 3',5'-cyclic monophosphate is not sufficient to augment interleukin-1beta-induced release of interleukin-6. The significance of interleukin-6 in the intraocular inflammatory response is discussed in terms of its proposed role in an endogenous antiinflammatory system acting through induction of interleukin-1 receptor antagonist, soluble tumor necrosis factor receptor, acute-phase proteins and corticosteroids.
authors.affiliation: Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA.
authors.forename: L N
authors.initials: LN
authors.lastname: Fleisher
authors.forename: M C
authors.initials: MC
authors.lastname: McGAHAN
authors.forename: J B
authors.initials: JB
authors.lastname: Ferrell
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D002924:Ciliary Body / Q000276:immunology* / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D016207:Cytokines / Q000276:immunology*; D004731:Endotoxins / Q000276:immunology; D007375:Interleukin-1 / Q000276:immunology; D015850:Interleukin-6 / Q000096:biosynthesis*; D010857:Pigment Epithelium of Eye / Q000276:immunology* / Q000378:metabolism; D011817:Rabbits; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology
chemical_list: D016207:Cytokines; D004731:Endotoxins; D007375:Interleukin-1; D015850:Interleukin-6; D014409:Tumor Necrosis Factor-alpha; D000242:Cyclic AMP