IMMUNOCYTOCHEMICAL CHARACTERIZATION OF PROTEINS SECRETED BY RETINAL-PIGMENT EPITHELIUM IN RETINAS OF NORMAL AND ROYAL-COLLEGE OF SURGEONS DYSTROPHIC RATS

In a previous study, an antigen consisting of proteins secreted by ret inal pigment epithelial (RPE) cells was injected into a sheep and the specificity of the resulting antiserum was shown by Western blotting a nd its effects on retinal development were determined in vitro and in vivo. In the present study, the distribution of these secreted protein s was determined by light microscopy immunocytochemistry in cultured n eonatal rat RPE cells and retinas of normal and Royal College of Surge ons (RCS) dystrophic rats and cerebrum of normal adult rats. Immunolab elling for these RPE-secreted proteins was detected in cytoplasmic ves icles surrounding nuclei and within processes of cultured normal and t ransformed rat RPE. In retinas of late postnatal and adult rats, dense immunostaining was found in the cytoplasm of RPE cells and ganglion c ell bodies. In addition to RPE and ganglion cells, scattered photorece ptors within the thin outer nuclear layer and small structures within the debris zone were also densely immunoreactive in retinas of 2-mo-ol d RCS dystrophic rats. The numbers of immunostained ganglion cells app eared to decrease in retinas of older RCS rats, although the immunorea ctivity within the RPE appeared to increase in density. No other neuro n within the retina, i.e. bipolar, amacrine or horizontal, was immunor eactive for RPE-secreted proteins. In the cerebral cortex of adult rat s, immunoreactivity for RPE-secreted proteins was primarily detected w ithin large perikarya of pyramidal neurons and smaller granule neurons . In conclusion, we report an immunocytochemical analysis of an antise rum raised against secreted proteins of rat RPE. This antiserum recogn ised proteins within secretory-like vesicles of cultured neonatal norm al and transformed rat RPE and showed a specificity for RPE and gangli on cells :in normal rat retinas, that appeared to be developmentally r egulated, and neuron perikarya in adult rat cerebrum.