In a previous study, an antigen consisting of proteins secreted
by retinal pigment epithelial (RPE) cells was
injected into a sheep and the specificity of the resulting antiserum
was shown by Western blotting and its
effects on retinal development were determined in vitro and in vivo.
In the present study, the distribution of
these secreted proteins was determined by light microscopy
immunocytochemistry in cultured neonatal rat
RPE cells and retinas of normal and Royal College of Surgeons
(RCS) dystrophic rats and cerebrum of
normal adult rats. Immunolabelling for these RPE-secreted proteins
was detected in cytoplasmic vesicles
surrounding nuclei and within processes of cultured normal and
transformed rat RPE. In retinas of late
postnatal and adult rats, dense immunostaining was found in the
cytoplasm of RPE cells and ganglion cell
bodies. In addition to RPE and ganglion cells, scattered photoreceptors
within the thin outer nuclear layer
and small structures within the debris zone were also densely
immunoreactive in retinas of 2-mo-old RCS
dystrophic rats. The numbers of immunostained ganglion cells
appeared to decrease in retinas of older RCS
rats, although the immunoreactivity within the RPE appeared to
increase in density. No other neuron within
the retina, i.e. bipolar, amacrine or horizontal, was immunoreactive
for RPE-secreted proteins. In the
cerebral cortex of adult rats, immunoreactivity for RPE-secreted
proteins was primarily detected within
large perikarya of pyramidal neurons and smaller granule neurons. In conclusion,
we report an
immunocytochemical analysis of an antiserum raised against
secreted proteins of rat RPE. This antiserum
recognised proteins within secretory-like vesicles of
cultured neonatal normal and transformed rat RPE and
showed a specificity for RPE and ganglion cells in normal
rat retinas, that appeared to be developmentally
regulated, and neuron perikarya in adult rat cerebrum.