Tumor necrosis factor production and receptor expression by a human malignant glioma cell line, D54-MG

Human malignant gliomas possess some of the same immune-related functions as astrocytes do. For instance, they are capable of secreting various immunoregulatory molecules and expressing HLA-DR antigens on their surface. The human malignant glioma cell line, D54-MG, was used to investigate the proliferation effects of tumor necrosis factor-α (TNF-α) and the expression of specific surface receptors for TNF-α. Additionally, we were interested in examining whether D54-MG cells are capable of synthesizing and secreting biologically active TNF-α. D54-MG cells responded in a mitogenic fashion upon incubation with TNF-α for 48 h under serum-free conditions. ¹²⁵I-labeled TNF-α was used in this study to investigate the expression of receptors specific for TNF-α on D54-MG cells. Scatchard analysis of our receptor binding data produced curvilinear plots indicating there are two distinct receptor sites for TNF-α. From these data, we calculated that there are approximately 3500 high affinity and 24,666 low affinity binding sites per cell. Pretreating these cells with interferon-γ (IFN-γ) resulted in a 2-fold increase in the number of high affinity binding sites and a moderate increase in the number of low affinity binding sites, with no appreciable change in binding affinity (K_d) of either site. D54-MG cells were unable to constitutively secrete TNF-α; however, upon stimulation, these cells synthesize and secrete biologically active TNF-α. Polyclonal antisera reactive with human macrophage-derived TNF-α neutralized the cytotoxicity of D54-MG-derived TNF-α, demonstrating that the cytotoxic activity was in fact due to TNF-α. Our observations indicate that TNF-α could act in an autocrine fashion to induce the proliferation of this malignant glioma cell line and that TNF-α exerts its effect by binding to specific TNF-α receptors whose expression was enhanced by IFN-γ.