Interphotoreceptor retinoid-binding protein in the cone matrix sheath. Electron microscopic immunocytochemical localization.

Using a monoclonal antibody to chondroitin 6-sulfate, a major constituent of the cone matrix sheath, the location of the cone matrix sheath and the relative distribution of interphotoreceptor retinoid-binding protein (IRBP) was examined by light and electron microscopic immunocytochemistry. Chondroitin 6-sulfate immunoreactivity was localized to regions surrounding cone outer and inner segments, extending from the pigment epithelium to the outer limiting membrane. Only a background level of chondroitin 6-sulfate immunoreactivity was found around rods. Ultrathin sections reacted with antibodies to IRBP and chondroitin 6-sulfate showed the presence of both in the matrix surrounding the cones. Chondroitin 6-sulfate immunoreactivity extended from cone inner and outer segments to the adjoining interphotoreceptor matrix (IPM) surrounding the rods, but only background labeling was observed around the rods. The label for IRBP was found in the region containing chondroitin 6-sulfate and the IPM surrounding the rod photoreceptors. The label for IRBP and chondroitin 6-sulfate appeared to be associated with the filamentous reticulum of the IPM. These findings not only show that the cone matrix sheath has not collapsed and that IRBP is present in the cone matrix sheath, but they also demonstrate retention of structural components of the IPM.