Abstract
Abstract: :
Purpose: To determine whether retinal pigment epithelium (RPE) contributes to immune privilege in the subretinal space by secreting immunosuppressive factors. Method: Posterior eyecups comprised of a healthy RPE layer resting on an intact choroids and sclera were created ex-vivo by removing from the anterior segment and retina from enucleated eyes of normal C57BL/6 mice and from mice treated 48 hr previously with i.v. injection of sodium iodate. These eye-cups were placed (RPE layer up) in culture wells and incubated at 37C with serum free medium for defined intervals. Supernatants (SN) were removed and assayed in vitro for capacity to suppress T cells proliferation and IFN-γ production by T cells and content of latent/active TGF-ß1 and TGF-ß2 by ELISA and mink lung cell bioassay. Result: As early as 6 hr after incubation, SN of normal eyecups inhibited both T cell proliferation and IFN-γ production by T cells, an effect that was maximal and profound in 24 hr SN. Latent TGF-ß2 was detected in 1 hr SN, but active TGF-ß2 was not detected until SN was obtained from 12 hr (and longer) eyecup incubations. SN suppression of T cell proliferation was partially relieved by neutralizing anti-TGF-ß antibodies. SN of posterior eyecups of sodium iodate treated donors poorly inhibited T cell proliferation. These SN contained both TGF-ß1 and -2 and the concentration of active TGF-ß was significantly less as compared with the eyecup SN from normal mice. Conclusion: Considering the SN of posterior eyecups as a major contributor to the subretinal space, these results indicate that RPE infuse this space with TGF-ß2 and the capacity to inhibit T cell activation. This capacity is lost if RPE are poisoned, and this correlates with the loss of immune privilege in the subretinal space.
Keywords: 567 retinal pigment epithelium • 433 immune tolerance/privilege • 435 immunomodulation/immunoregulation