Small heat shock protein αA-crystallin prevents photoreceptor degeneration in experimental autoimmune uveitis.

The small heat shock protein, αA-crystallin null (αA-/-) mice are known to be more prone to retinal degeneration than the wild type mice in Experimental Autoimmune Uveoretinitis (EAU). In this report we demonstrate that intravenous administration of αA preserves retinal architecture and prevents photoreceptor damage in EAU. Interestingly, only αA and not αB-crystallin (αB), a closely related small heat shock protein works, pointing to molecular specificity in the observed retinal protection. The possible involvement of αA in retinal protection through immune modulation is corroborated by adaptive transfer experiments, (employing αA-/- and wild type mice with EAU as donors and Rag2-/- as the recipient mice), which indicate that αA protects against the autoimmune challenge by modulating the systemic B and T cell immunity. We show that αA administration causes marked reduction in Th1 cytokines (TNF-α, IL-12 and IFN-γ), both in the retina and in the spleen; notably, IL-17 was only reduced in the retina suggesting local intervention. Importantly, expression of Toll-like receptors and their associated adaptors is also inhibited suggesting that αA protection, against photoreceptor loss in EAU, is associated with systemic suppression of both the adaptive and innate immune responses.

Pathogenic role of retinal microglia in experimental uveoretinitis.

PURPOSE: To devise methods for unequivocal identification of activated retinal microglia in experimental autoimmune uveoretinitis (EAU) and to investigate their role in the development of EAU. METHODS: A group of Lewis rats underwent optic nerve axotomy with the application of N-4-(4-didecylaminostyryl)-N methylpyridinium iodide (4Di-10ASP) at the axotomy site. On days 3, 14, and 38 after axotomy, the rats were killed, the eyes were enucleated, and the retinas were stained for OX42. Another group of such axotomized rats were immunized with S-antigen peptide and were killed on days 7 through 12 after the injection with peptide. The enucleated eyes were stained for OX42 and examined by confocal microscope. After axotomy, bone marrow (Y-->X) chimeric rats were injected with S-antigen peptide and were killed on days 10 and 12 after injection. The retinas were evaluated by PCR with Y-specific primers. Finally, a group of axotomized rats was injected with the S-antigen peptide and killed on days 6, 8, 9, and 10 after injection. Their enucleated eyes were examined for microglial expression of TNFalpha and for generation of peroxynitrite. RESULTS: In the axotomized, non-EAU eyes, 4Di-10ASP-labeled ganglion cells were detectable on days 3 and 14, and 4Di-10ASP-containing OX42-positive cells (microglia) were found in the nerve fiber and other inner retinal layers on days 14 and 38. The S-antigen peptide-injected rats showed migration of the microglia (4Di-10ASP-positive and OX42-positive) to the photoreceptor cell layer on day 9, and these cells increased in number at this site on day 10. No macrophages (OX42-positive and 4Di-10ASP-negative) were present at this early stage of EAU, but such cells appeared in the retina on days 11 and 12. PCR of the chimeric EAU retinas showed an absence of the Y chromosome-amplified product on day 10, but the presence of this product was detected on day 12. The expression of TNFalpha and generation of peroxynitrite were noted in the migrated microglia at the photoreceptor cell layer on days 9 and 10 of EAU. CONCLUSIONS: In the early phase of EAU, the microglia migrate to the photoreceptor cell layer where they generate TNFalpha and peroxynitrite. Such microglial migration and activation take place before infiltration of the macrophages. These findings indicate a novel pathogenic mechanism of EAU, in which retinal microglia may initiate retinitis with subsequent recruitment of circulation-derived phagocytes, leading to the amplification of uveoretinitis.