INDUCTION OF TUMOR-NECROSIS-FACTOR-ALPHA IN HUMAN NEURONAL CELLS BY EXTRACELLULAR HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 TAX(1)

To examine the role of human T-lymphotropic virus type 1 (HTLV-I) Tax( 1) in the development of neurological disease, we studied the effects of extracellular Tax(1) on gene expression in NT2-N cells, postmitotic cells that share morphologic, phenotypic, and functional features wit h mature human primary neurons, Treatment with soluble HTLV-1 Tax(1) r esulted in the induction of tumor necrosis factor alpha (TNF-alpha) ge ne expression, as detected by reverse-transcribed PCR and by enzyme-li nked immunosorbent assay, TNF-alpha induction was completely blocked b y clearance,vith anti-Tax(1) monoclonal antibodies, Furthermore, cells treated with either a mock bacterial extract or with lipopolysacchari de produced no detectable TNF-alpha, Synthesis of TNF-alpha in respons e to soluble Tax(1) occurred in a dose-dependent fashion between 0.25 and 75 nM and peaked within 6 h of treatment, Interestingly, culturing NT2-N cells in the presence of soluble Tax(1) for as little as 5 min was sufficient to result in TNF-alpha production, indicating that the induction of TNF-alpha in NT2-N does not require Tax(1) to be continua lly present in the culture medium, Treatment of the undifferentiated p arental embryonal carcinoma cell line NT2 with soluble Tax(1) did not result in TNF-alpha synthesis, suggesting that differentiation-depende nt, neuron-specific factors may be required, These results provide the first experimental evidence that neuronal cells are sensitive to HTLV -1 Tax(1) as an extracellular cytokine, with a potential role in the p athology of HTLV-1-associated/tropical spastic paraparesis.