Immunofluorescent cytometry and electron microscopic immunolocalization of insulin-like growth factor (IGF)-II...

The choroid plexus contains receptors for insulin-like growth factor (IGF)-II, it synthesizes IGF-II, and it secretes soluble IGF binding proteins with high affinity for IGF-II. Although the actions of IGFs in the choroid plexus are unknown, IGFs may participate in CNS growth and differentiation, CNS injury/repair mechanisms, regulation of satiety, and growth hormone secretion. Because the choroid plexus is a heterogeneous tissue containing several cell types, to study the role of IGF-II in the choroid plexus we need to know precisely which cells contain IGF-II receptors. Therefore, we studied the distribution of IGF-II receptors in infant rat choroid plexus by electron microscopic immunohistochemistry and immunofluorescent cytometry of dispersed choroid plexus cells using a well-characterized, highly specific rabbit anti-rat IGF-II receptor antibody. These studies show that IGF-II receptors are detectable in large quantities in both choroid plexus epithelial cells and in the fenestrated capillary endothelial cells. Results were confirmed by immunofluorescent cell sorting using the anti-IGF-II receptor antiserum. Other cell types in the choroid plexus contained lower levels of immunoreactivity, including red blood cells. Physiological studies of IGF-II effects on intact choroid plexus may, therefore, reflect effects on both of these cell populations. These data provide a compelling rationale for the development of choroid plexus epithelial cell lines or pure culture techniques to study the physiology of IGF-II in individual cell types.