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R Liao, GI Liou, F Gonzalez-Fernandez; Distribution of Albumin in Normal and IRBP -/- Mice . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2611.
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Adler and Edwards (Exp Eye Res. 70: 227-37, 2000), but not Vinores et al. (Hist & Histopath. 10:913-23, 1995) have identified albumin as a normal component of the human interphotoreceptor matrix (IPM). It has been proposed that albumin is a surrogate carrier of visual cycle retinoids in transgenic mice lacking IRBP (IRBP -/-). Although mRNA for IRBP has been detected in the normal mouse retina (Dodson et al. Cur Eye Res. 22:182-89, 2001), to our knowledge immunohistochemical studies of albumin in the retina of rodents have not been carried out. Purpose: To provide a detailed characterization of the distribution of albumin within the retina of normal mice and IRBP -/- mice. Methods: Cryosections of whole eyes from light adapted C57b1/6 and IRBP -/- mice were studied by direct immunofluorescence using a FITC-labeled rabbit IgG directed against mouse albumin. A range of antibody dilutions were examined. Controls included preadsorbed studies using purified mouse albumin. Results: Immunofluorescence showed varying levels of albumin in the ocular structures. At an antibody dilution of 1:1000 the most prominent staining was over the outer segment region presumably the IPM. At 1:800, staining of the outer plexiform layer and retinal vessels became apparent. Albumin was also present within Bruch's membrane and the walls of the choroidal vessels. At 1:400, the overall intensity of IPM, Bruch's membrane and vascular staining were most intense. At 1:250, background signal within the sclera and retinal interneurons became apparent. Immunofluoresecence for albumin was similar in the IRBP -/- retina although the IPM staining appeared less prominent in many regions. Conclusion: Albumin is present in a variety of locations in the normal retina. The highest concentration appears to be within the IPM. Significant immunospecific fluorescence was also seen in Bruch's membrane and the walls of the choroidal and retinal vessels. The localization of albumin was similar in the IRBP -/- mice although the intensity of the IPM staining appeared reduced. Ongoing studies are examining the source of the albumin in the IPM and the mechanism of its remarkable accumulation in the subretinal space.
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