Faculty Bibliography

Medium of untreated human FS-4 foreskin fibroblasts contained a factor which, upon the addition of exogenous tumor necrosis factor (TNF), inhibited encephalomyocarditis virus replication when neither medium alone nor TNF alone were effective. This antiviral activity was abolished by a monoclonal antibody to human interferon (IFN)-beta, suggesting that the active component in the medium from untreated FS-4 cells was IFN-beta, present at subeffective concentrations. In addition, we show that untreated FS-4 cells contain IFN-beta mRNA, demonstrable by the highly sensitive polymerase chain reaction after reverse transcription. Treatment of FS-4 cells with TNF produced an approximately 16-fold increase in the steady-state level of IFN-beta mRNA. Our results support the conclusion that autocrine IFN-beta is secreted by untreated normal fibroblasts and that TNF can enhance the production of autocrine IFN-beta by increasing the level of IFN-beta mRNA. Our study also demonstrates that subeffective concentrations of autocrine IFN-beta, which escape detection in conventional assays, are sufficient to produce a strong synergistic action with TNF

Recombinant human interleukin 6 (IL-6), also termed B-cell-stimulatory factor 2 (BSF-2) or interferon-beta 2, was found to stimulate the proliferation of mouse thymocytes costimulated with phytohemagglutinin (PHA). In addition, IL-6 synergistically enhanced the stimulation of thymocyte proliferation by recombinant human interleukin 1 (IL-1) or interleukin 2 (IL-2). Mature thymocytes lacking peanut agglutinin receptor are the main target of IL-6 action. Incubation of thymocytes with IL-6 in the presence of PHA resulted in an increased expression of the IL-2 receptor (IL-2R) as demonstrated by flow cytometry. Monoclonal antibody specific for the p55 chain of the murine IL-2R significantly reduced IL-6-stimulated thymocyte proliferation in the presence of the optimal concentration of PHA. However, the same monoclonal antibody failed to reduce IL-6-driven thymocyte proliferation in the presence of a suboptimal PHA concentration, suggesting that IL-6 stimulates thymocyte proliferation by way of IL-2-dependent and IL-2-independent pathways. These results indicate that, in addition to its earlier demonstrated ability to promote B-cell differentiation and growth, IL-6 also acts as a growth regulator in cells of the T-lymphocyte lineage. IL-6 is emerging as an important regulatory cytokine with multiple actions on immune functions

Although tumor necrosis factor (TNF) and interleukin 1 (IL-1) affect many cell functions, the molecular mechanisms of TNF and IL-1 action are not understood. Our present study shows that exposure of human FS-4 fibroblasts to TNF or IL-1 caused a rapid accumulation of intracellular cAMP and an increase in protein kinase activity. Intracellular cAMP levels peaked 3-5 min after the addition of TNF or IL-1 and returned to basal level by 15 min. Increased phosphorylation of histone HII-B protein was demonstrated with extracts prepared from TNF- or IL-1-treated cells, suggesting an increase in cAMP-dependent protein kinase activity. No evidence was obtained for protein kinase C activation in TNF-treated FS-4 cells. TNF, IL-1, and forskolin all stimulated interleukin 6 (IL-6) mRNA levels in FS-4 cells. The protein kinase inhibitor H-8, inhibiting preferentially cAMP-dependent kinase activity, reduced forskolin-stimulated IL-6 mRNA induction more strongly than TNF- or IL-1-driven IL-6 mRNA induction. These results suggest that activation of cAMP-dependent protein kinase by TNF and IL-1 is important in some actions of these cytokines. In addition, our data on IL-6 induction by TNF and IL-1 suggest that other, yet unidentified, signal transduction mechanisms contribute to TNF and IL-1 actions on gene expression in human fibroblasts

Earlier studies showed that both tumor necrosis factor (TNF) and interleukin-1 (IL1) can inhibit virus replication in cultured cells. However, in human FS-4 fibroblasts, in which recombinant human TNF protected cells from encephalomyocarditis (EMC) virus infection, recombinant human IL1 alpha and IL1 beta failed to induce antiviral protection. Moreover, both forms of IL1 inhibited the development of the TNF-induced antiviral state. To elucidate the mechanism of this inhibition, we examined the effect of IL1 on the synthesis of interferon-beta (IFN-beta), stimulated with polyinosinate.polycytidylate [poly(I).poly(C)]. When added 2 h or more before poly(I).poly(C), both forms of IL1 had a strong inhibitory effect on IFN-beta synthesis, as determined by antiviral assay of the IFN-beta protein or by quantitation of IFN-beta mRNA levels in Northern blot analysis. However, when IL1 was added simultaneously with poly(I).poly(C), or 2 h after poly(I).poly(C), IFN-beta synthesis was increased. The inhibitory action of IL1 on poly(I).poly(C)-induced IFN-beta synthesis was abolished in the presence of cycloheximide, suggesting that it is mediated indirectly by an IL1-induced product in the FS-4 cells. In addition to its ability to inhibit IFN-beta synthesis, IL1 also caused a partial reversal of the antiviral action of IFN-beta. In contrast to IL1, TNF did not inhibit IFN-beta synthesis, nor did it interfere with the antiviral action of IFN-beta. Simultaneous addition of TNF and poly(I).poly(C) to FS-4 cells enhanced IFN-beta synthesis. Under proper conditions TNF and IFN-beta showed an additive antiviral effect

Interleukin 6 (IL-6; also referred to as interferon-beta 2, 26-kDa protein, and B cell stimulatory factor 2) is a cytokine whose actions include a stimulation of immunoglobulin synthesis, enhancement of B cell growth, and modulation of acute phase protein synthesis by hepatocytes. Synthesis of IL-6 is stimulated by interleukin 1 (IL-1), tumor necrosis factor (TNF), or platelet-derived growth factor. We examined the role of the cyclic AMP (cAMP)-dependent signal transduction pathway in IL-6 gene expression. Several activators of adenylate cyclase, including prostaglandin E1, forskolin, and cholera toxin, as well as the phosphodiesterase inhibitor isobutylmethylxanthine and the cAMP analog dibutyryl cAMP, shared the ability to cause a dramatic and sustained increase in IL-6 mRNA levels in human FS-4 fibroblasts. Actinomycin D treatment abolished this enhancement. Treatments that increased intracellular cAMP also stimulated the secretion of the IL-6 protein in a biologically active form. Increased intracellular cAMP appears to enhance IL-6 gene expression by a protein kinase C-independent mechanism because down-regulation of protein kinase C by a chronic exposure of cells to a high dose of 12-O-tetradecanoylphorbol 13-acetate did not abolish the enhancement of IL-6 expression by treatments that increase cAMP. IL-1 and TNF too increased IL-6 mRNA levels by a protein kinase C-independent mechanism. Our results suggest a role for the cAMP-dependent pathway(s) in IL-6 gene activation by TNF and IL-1