Induction of membrane-associated interleukin 1 by tumor necrosis factor in human fibroblasts

Highly purified recombinant human tumor necrosis factor (TNF) was found to induce interleukin 1 (IL 1) production in diploid human FS-4 fibroblasts. Demonstration of IL 1 activity was based on the ability of TNF-treated FS-4 cells, subsequently fixed with formaldehyde, to stimulate thymocyte proliferation in the presence of phytohemagglutinin. Incubation of FS-4 cells with the optimal dose of TNF (10 ng/ml) resulted in a marked increase in [3H] thymidine uptake by thymocytes co-cultured with formaldehyde-fixed FS-4 cells. Induction of this apparently membrane-associated IL 1 (MA-IL 1) activity was demonstrable at 6 hr and reached a plateau after 48 hr of incubation with TNF. FS-4 cells did not secrete soluble IL 1 in response to TNF. Dexamethasone suppressed the synthesis of TNF-induced MA-IL 1. A monoclonal antibody specific for TNF neutralized MA-IL 1 induction, indicating that the induction is due to TNF, and not to a contaminant in the TNF preparation. The ability of TNF to induce IL 1 synthesis in FS-4 fibroblasts at the transcriptional level was confirmed by S1 nuclease protection assay. Cytoplasmic RNA from uninduced FS-4 cells contained no demonstrable RNA hybridizing with a human IL 1-alpha cDNA probe and low levels of RNA hybridizing with an IL 1-beta cDNA. Induction with TNF resulted in the appearance of IL 1-alpha mRNA and a very significant increase in IL 1-beta mRNA, indicating that TNF induces the synthesis of both IL 1-alpha and IL 1-beta in FS-4 cells.