Interleukin-6 production by murine macrophage cell lines P388D1 and J774A.1: stimulation requirements and kinetics.

The murine macrophage tumor lines, P388D1 and J774A.1 were stimulated with LPS, IL-6, IL-1 alpha, TNF-alpha, IFN-gamma, PMA, or combinations of these reagents to induce the production of IL-6, IL-1, and TNF-alpha. Using Northern blot analysis and bioassays for the detection of cytokine production, it was noted that identical stimuli induced all three inflammatory mediators. However, unlike fibroblasts or endothelial cells, neither P388D1 nor J774A.1 macrophages respond to IL-1 alpha or TNF-alpha by producing IL-6. The results imply that these cytokines are not autoregulatory for macrophages and may be tissue-specific in their stimulatory effects. IFN-gamma and PMA synergize with LPS in the production of IL-6 as well as IL-1 and TNF-alpha. These observations suggest that IFN-gamma may mediate amplification pathways important in the production of inflammatory mediators. Kinetic studies on the transcription of mRNA and secretion of IL-6, IL-1, and TNF-alpha revealed that TNF-alpha mRNA transcription and cytokine production occur very rapidly. TNF-alpha mRNA accumulation peaked 1-2 hr after stimulation and maximum concentrations of cytokine are found in supernatants collected after 2-4 hr of culture. IL-6 and IL-1 alpha mRNA accumulation peaked simultaneously after 4-8 hr. However, IL-6 bioactivity peaks between 8 and 12 hr whereas maximum concentrations of IL-1 bioactivity are not detected in supernatants from stimulated cells collected prior to 12 hr of culture. Thus even though TNF-alpha production precedes that of IL-1 and IL-6, and stimulates IL-6 production in fibroblasts, there is no evidence that TNF-alpha acts to amplify the production of IL-6 or IL-1 by murine macrophage cell lines. The results suggest differential regulation of IL-6 expression between fibroblasts and macrophages.