Abstract
Abstract: :
Purpose: We have shown that subconjunctival delivery of a plasmid encoding α–MSH suppresses the incidence and severity of experimental autoimmune uveitis (EAU) in wild type mice, but not in mice lacking the melanocortin 5 receptor (MC5r). While the clinical signs of EAU are significantly suppressed in α–MSH plasmid–treated eyes, the effects of treating the eyes with the α–MSH plasmid on retinal structure is not known. Therefore, we examined the pathology of retinas in EAU eyes that were treated with the α–MSH plasmid. Methods:EAU was induced in B10.RIII, C57/Bl6, or MC5r–/– mice by subcutaneous injection of interphotoreceptor retinoid binding protein peptide emulsified in Complete Freund’s Adjuvant. The mice received into both eyes 2 subconjunctival injections delivered 3 days apart just after the onset of clinical EAU of either 25 µg α–MSH plasmid or empty plasmid. After the peak of EAU we collected and formalin–fixed the eyes of immunized mice representing the mean maximum EAU score from each treatment group. The eyes were sectioned and stained with hematoxylin and eosin. We evaluated the retinal structures for infiltration of inflammatory cells, retinal detachment and folding, and loss of retinal cell layers. Results: Retinas of the α–MSH plasmid–treated EAU wild type mice showed marked reduction in retinal detachment, folding, granuloma formation, and vasculitis immediately following peak of clinical inflammation in contrast to retinas of wild type EAU mice receiving empty plasmid. Further, in α–MSH plasmid–treated wild type EAU eyes the photoreceptor outer segments and outer nuclear layer structures were preserved in contrast to wild type EAU eyes receiving the empty plasmid. Retinas from α–MSH plasmid–treated EAU eyes of MC5r–/– mice exhibited extensive disorganization, characterized by detachments, folds, vasculitis, intraretinal granulomas, and photoreceptor segment and outer nuclear cell loss. This was similar to eyes of MC5r–/– mice treated with the empty plasmid. Inflammatory cells were present in the vitreal cavity of all eyes examined, including α–MSH plasmid–treated eyes. Conclusion: Delivery of α–MSH–encoding plasmid into eyes with EAU spares the retina from immune–mediated destruction. This protective effect of α–MSH is dependent on the expression of MC5r. This implies that the α–MSH treatment of EAU eyes promotes both suppression of inflammation and protection of the retina.
Keywords: gene transfer/gene therapy • immunomodulation/immunoregulation • immune tolerance/privilege