POLARIZED SECRETION OF IL-6 AND IL-8 BY HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

A number of cell types situated along interfaces of various tissues an d organs such as the peritoneum and the intestine have been shown to s ecrete inflammatory cytokines in a polarized fashion. Retinal pigment epithelial (RPE) cells are positioned at the interface between the vas cularized choroid and the avascular retina, forming part of the blood- retina barrier. These cells are potent producers of inflammatory cytok ines and are therefore considered to play an important role in the pat hogenesis of ocular inflammation. Whether cytokine secretion by these cells also follows a vectorial pattern is not yet known, and was there fore the subject of this study. Monolayers of human RPE cells (primary cultures and the ARPE-19 cell line) cultured on transwell filters wer e stimulated to produce IL-6 and IL-8 by adding IL-1 beta (100 U/ml) t o either the upper or the lower compartment. After stimulation, the hu man RPE cell lines showed polarized secretion of IL-6 and IL-8 towards the basal side, irrespective of the side of stimulation. The ARPE-19 cell line also secreted IL-6 and IL-8 in a polarized fashion towards t he basal side after basal stimulation; polarized secretion was, howeve r, not apparent after apical stimulation. The observation that human R PE cells secrete LL-6 and IL-8 in a polarized fashion towards the chor oid may represent a mechanism to prevent damage to the adjacent fragil e retinal tissue.