RPE Cells Use PEDF And MIF to Confer Innate Immune Privilege On The Subretinal Space

Abstract

Abstract: : Purpose:To determine whether retinal pigment epithelial cells (RPE) confer innate immune privilege upon the subretinal space by inhibiting the activation of macrophages and suppressing NK cell–mediated cytotoxicity. Methods:Posterior eyecups were prepared by excising the anterior segment, lens and retina from enucleated C57BL/6 eyes, leaving behind a healthy monolayer of RPE resting on choroid and sclera. Serum free medium was added to these RPE eyecups and after 24 hour, supernatants (SN) were removed and tested for their capacity (a) to modulate IL–10 and IL–12 release from LPS–activated macrophages, using ELISA, and (b) to inhibit lysis of YAC–1 target cells by poly I:C stimulated NK cells from C57BL/6 mice. Neutralizing anti–PEDF, or anti–MIF antibodies were added to some assays, and as controls, recombinant PEDF and IL–10 were added to some assays instead of RPE SN. RT–PCR was used to determine IL–10 mRNA levels in macrophages exposed to RPE SN or PEDF. Results:RPE supernatants, as well as recombinant PEDF, enhanced significantly IL–10 message levels and secretion, but inhibited IL–12 production by activated macrophages. Anti–PEDF Ab reversed SN–induced IL–12 inhibition and led to suppression of IL–10 production by macrophages. RPE SN also inhibited the capacity of NK cells to lyse YAC–1 target cells, an effect that was neutralized in the presence of anti–MIF Ab. Conclusions:In posterior eyecups, RPE secrete PEDF and MIF which in turn suppress macrophage IL–12 production and NK cell–mediated target cell lysis. By promoting IL–10 secretion by activated macrophages, PEDF re–inforces the innate immune privileged status of the subretinal space. To our knowledge, this is the first report of a role for PEDF in controlling effector cells of the innate immune system.

Keywords: immunomodulation/immunoregulation • retinal pigment epithelium • immune tolerance/privilege