Induction of tumor necrosis factor synthesis in human monocytes treated by transcriptional inhibitors

Human blood monocytes and lymphocytes were separated by Percoll gradient fractionation. The synthesis of RNA was inhibited by actinomycin D (AcD) or alpha-amanitin (Amn). Monocytes were stimulated with LPS, lymphocytes were stimulated with phytohaemagglutinin (PHA). The activity of tumor necrosis factor (TNF-alpha) and lymphotoxin (LT) was measured by L-929 cell assay. It was shown that induction of TNF-alpha synthesis by LPS was not blocked by AcD and Amn. In contrast, the production of LT was blocked in cultures of lymphocytes treated by the inhibitors. Moreover, TNF-alpha synthesis was induced in resting monocyte cultures by AcD. Cycloheximide (Cy) inhibited the production of TNF-alpha. The data imply that TNF-alpha synthesis by human blood monocytes can be induced by posttranscriptional regulation of TNF-alpha mRNA presynthesized in vivo.