Abstract

Astrocyte-enriched populations were established from human embryonic brain analyzed for their ability to synthesize cytokines potentially relevant for mechanisms of inflammation and immunity in the brain. Unstimulated astrocytes did not secrete significant IL-6, IL-8, macrophage CSF (M-CSF), granulocyte-macrophage CSF (GM-CSF), or granulocyte-CSF (G-CSF), as determined by specific ELISA and/or bioassay. With the exception of M-CSF mRNA, transcripts for the above factors were not detected in unstimulated astrocytes. On exposure of human astrocytes to IL-1 beta, high levels of IL-6, IL-8, M-CSF, G-CSF, and GM-CSF mRNAs were detected; moreover, active secretion of all the above cytokines was demonstrated. TNF-alpha was also able to stimulate IL-6, IL-8, M-CSF, GM-CSF, and G-CSF synthesis and secretion, but was generally less potent than IL-1 beta. No IL-3 mRNA or protein was detected in unstimulated or cytokine-treated astrocytes. IL-1 alpha and IL-1 beta mRNAs and proteins were not detected in unstimulated astrocytes, but were present in very small amounts after stimulation with TNF-alpha/IL-1 beta. No IL-6, M-CSF, GM-CSF, G-CSF, or IL-8 were induced by IL-1 beta or TNF-alpha in early primary cultures, which mainly contain undifferentiated neuronal/glial progenitor cells. These studies demonstrate for the first time the production of multiple cytokines by normal human astrocytes stimulated in culture by IL-1 beta and TNF-alpha. The capacity of human astrocytes to synthesize and release cytokines active on hemolymphopoietic cells supports the concept that these cells play an important role in the regulation of inflammatory and immune responses in a variety of brain pathologies.