Demonstration of interleukin‐3 receptor‐associated antigen in the central nervous system

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Abstract
We previously reported that interleukin‐3 (IL‐3) acts as a neurotrophic factor for cholinergic neurons. However, it has not yet been determined whether the action is derived from the interaction of IL‐3 with IL‐3 receptors. As the first step to study IL‐3 receptors in the central nervous system, we examined the presence and localization of IL‐3 receptor‐associated antigen (IL‐3RAA) in mouse and rat brain. Immunohistochemically, IL‐3RAA, which is closely involved both in the IL‐3 binding to IL‐3 receptors and the tyrosine phosphorylation in the signal transduction for IL‐3 in hematopoietic cells, was demonstrated in neurons throughout the brain. This was confirmed in primary cultured neurons and neuronal cell lines by immunocytochemistry and flow cytometry. The staining intensity varied among regions and the most intense immunoreactivity for IL‐3RAA was found in large neurons in the magnocellular basal nuclei, pyramidal cells in the cerebral cortex, and neuronal cells in some nuclei of the brainstem. Not only cholinergic cell lines derived from the septal region but also other neuronal cell lines exhibited IL‐3RAA immunoreactivity by flow cytometry. Therefore, we conclude that IL‐3RAA is present in a wide variety of neurons in the brain including cholinergic neurons of the basal forebrain. Western blot analysis revealed that the candidates for IL‐3RAA are 145, 100, and 50 kDa proteins both in neuronal and IL‐3‐dependent cell lines.