Pigment epithelial growth factor suppresses inflammation by modulating macrophage activation

To study the contribution of murine retinal pigment epithelial (RPE) cells to the innate immune-privilege status of the subretinal space as determined by the ability of pigment epithelial-derived factor (PEDF) and somatostatin (SOM), produced by RPE, to regulate macrophage-mediated inflammation.

Serum-free medium was added to RPE eyecups (a healthy monolayer of RPE resting on choroid and sclera) and the supernatants were removed after 24 hours (RPE SN). The RPE SN was assayed for the presence of PEDF and SOM and for its ability to regulate interleukin (IL)-12, IL-10, and nitric oxide (NO) production by resting and activated macrophages. A group of mice received intradermal injection of lipopolysaccharide (LPS) and PEDF in one ear and LPS alone in the other ear. Ear thickness was measured before- and 24 hours after ear injections.

Soluble factors present in the RPE SN inhibited IL-12 production and substantially increased IL-10 while having minimal effects on NO production by activated macrophages. The message for PEDF, SOM, and IL-10 was detected in RPE cells, and the protein for these factors was found in the RPE SN. The stimulation of IL-10 and suppression of IL-12 production by RPE-SN-treated macrophages was neutralized by anti-PEDF antibodies. Neutralization of SOM in the RPE SN, suppressed NO production by activated macrophages. Intradermal injection of PEDF substantially inhibited LPS-induced inflammatory response.

PEDF inhibits LPS-driven macrophage activation in vitro and in vivo. By producing PEDF, the RPE contributes to innate immune privilege of the eye.