Albumin is not present in the murine interphotoreceptor matrix, or in that of transgenic mice lacking IRBP

Purpose: The interphotoreceptor matrix mediates interactions between the retinal pigment epithelium, photoreceptors, and Müller cells. Each of these cells contributes to specific proteoglycans, proteins, and growth factors in the interphotoreceptor matrix. Some components, such as interphotoreceptor retinoid binding protein (IRBP), are virtually unique to the interphotoreceptor matrix. It has been proposed that serum albumin, thought to be present in the interphotoreceptor matrix, could act as a surrogate retinoid binding protein within the subretinal space of transgenic mice lacking interphotoreceptor retinoid binding protein. To address this question, we sought to determine whether albumin is present in the interphotoreceptor matrix of IRBP^+/+ mice or IRBP^-/- mice. Methods: We examined the distribution of albumin in IRBP^-/- mice and IRBP+/+ mice using immunofluorescence and immunoperoxidase histochemistry. Results: The distribution of albumin within the corneal stroma, sclera, and capillaries is consistent with previous work. Serum albumin could not be detected in the interphotoreceptor matrix. The distribution of albumin in IRBP^-/- mice was similar to that of their wildtype counterparts. Conclusions: Serum albumin is not a component of the interphotoreceptor matrix of IRBP^+/+ mice or IRBP^-/- mice.