Cytokine modulation of adhesion molecule expression on human retinal pigment epithelial cells

The purpose of this study was to assess qualitatively the expression of adhesion molecules by human retinal pigment epithelium (RPE) and to study their regulation by inflammatory cytokines. These molecular events and the role played by inflammatory cytokines are important for selective lymphocyte trafficking into the eye during uveitis.

Expression of intracellular adhesion molecule-1 (ICAM-1), endothelial leukocyte adhesion molecule-1 (ELAM-1), platelet endothelial cell adhesion molecule-1 (PECAM-1), and vascular adhesion molecule (VCAM-1) by early passage human RPE cells was assessed by flow cytometry. In addition, the regulation of the expression of these molecules by the inflammatory cytokines interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) was determined. Reverse transcription-polymerase chain reaction (RT-PCR) was used to characterize further adhesion molecule expression.

Flow cytometric analysis determined that ICAM-1 was constitutively expressed on RPE cell lines and that in the presence of TNF alpha, IFN gamma, and IL-1 beta, there was a median fold increase in expression of 4.4, 5.4, and 4.4, respectively. In contrast, flow cytometric analysis of ELAM-1, PECAM-1, and VCAM-1 indicated that these adhesion molecules were not constitutively expressed at the cell surface; only the expression of VCAM-1 was upregulated by the presence of cytokines. The results of RT-PCR on RPE cells indicated that mRNA for all the adhesion molecules was present constitutively in some RPE cultures. After activation with IFN gamma, TNF alpha, and IL-1 beta, RT-PCR analysis showed that the number of RPE cell lines expressing all the adhesion molecules increased.

ICAM-1 expression is markedly upregulated by inflammatory cytokines. Although mRNA for other adhesion molecules is expressed in RPE cells and is enhanced by inflammatory cytokines, this does not necessarily reflect the cell surface protein expression. Thus, the expression of adhesion molecules by RPE cells, and the subsequent recruitment of specific leukocytes, may be determined by the local cytokine environment.