Expression of tumor necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) mRNA in adult human astrocytes: comparison with adult microglia and fetal astrocytes.

Astrocytes and microglia are cell populations which are implicated as being capable of regulating and effecting immune responses within the central nervous system (CNS). These functions are postulated to be mediated at least in part by production of soluble protein molecules termed cytokines. In this study, we utilized dissociated cultures of glial cells prepared from adult and fetal CNS tissue and a combined in situ hybridization-immunocytochemical technique in order to compare expression of TNF alpha and IL-6 mRNA between adult and fetal astrocytes and between adult astrocytes and microglia. Our results, using digoxygenin-labeled riboprobes, indicate that in contrast to fetal astrocytes only rare adult astrocytes express TNF alpha and IL-6 transcripts under our serum-supplemented basal culture conditions. Activation with LPS and IFN gamma increased the proportion of adult astrocytes expressing detectable TNF alpha and IL-6 mRNA signals; however, the proportion was significantly less than for microglia contained in the same cultures. These results suggest that microglia rather than astrocytes are more likely to be sources of these cytokines within the adult human CNS. Further studies of cytokine expression by glial cells will need to consider both the age and species of the glial cells used.