Modulation of TNF-alpha mRNA production in rat C6 glioma cells by TNF-alpha, IL-1beta, IL-6, and IFN-alpha: in vitro analysis of cytokine-cytokine interactions.

Cytokines regulate the expression of other cytokines in the centrally derived rat C6 glioma cell line. However, the modulation of tumor necrosis factor-alpha (TNF-alpha, a pivotal proinflammatory cytokine) in C6 cells is unknown. Here we investigated the expression of TNF-alpha mRNA in C6 glioma cells in response to TNF-alpha, interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), and interferon-alpha (IFN-alpha). The data show that (1) IL-1beta induced a significant upregulation of TNF-alpha mRNA; (2) the effect of IL-1beta on TNF-alpha mRNA expression was completely blocked by the concomitant application of IL-1Ra, which suggests specificity of IL-1beta action through the IL-1 signaling receptor; (3) no detectable modulation of TNF-alpha mRNA expression was observed with the individual applications of TNF-alpha, IL-6, or IFN-alpha; (4) the concomitant treatments of TNF-alpha + IL-1beta or TNF-alpha + IL-1beta + IL-6 strongly upregulated TNF-alpha mRNA expression, whereas the concomitant application of TNF-alpha + IL-6 or IL-1beta + IL-6 induced a moderate increase; and (5) IFN-alpha significantly attenuated induction of TNF-alpha mRNA by TNF-alpha + IL-1beta + IL-6. Thus, IL-1beta, TNF-alpha and IL-6 interact to upregulate TNF-alpha mRNA expression synergistically, and IFN-alpha acts as an inhibitory cytokine in C6 glioma cells. These findings also suggest that the rat C6 glioma cell line may be used as an in vitro model to characterize cytokine-cytokine interactions.