The hematopoietic growth factor interleukin-3 (IL-3) promotes the proliferation and maturation of pluripotent myeloid progenitor cells. In the immune system, IL-3 is synthesized by mitogen or antigen- stimulated T lymphocytes. We demonstrate the expression of IL-3 mRNA in mouse brain by in situ hybridization histochemistry and Northern blot analysis. The IL-3 mRNA is localized in discrete areas of the brain and can be found in neuronal cell body and astrocytes. Northern analysis of cerebellar RNA, compared with mRNA extracted from WEHI-3 cells, showed a single hybridization band, approximately 1.2 kb, suggesting similar processing between brain and myeloid cells. The molecular evidence and previous observations of IL-3-like biologic activity found in the brain suggest a potential role for IL-3 in the neurobiology of the CNS.

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