Interleukin-4 inhibits interleukin-1 synthesis by a posttranscriptional mechanism.

T cell derived cytokines, interleukin-2 and interferon-gamma, are known to upregulate the interleukin-1 synthesis of monocyte/macrophages. The effect of a third T cell derived cytokine, interleukin-4, was now investigated. Human peripheral blood monocytes were activated with bacterial lipopolysaccharide in the presence or absence of interleukin-4 and the production of biologically active interleukin-1 was quantitated both from the culture supernatants and from the monocyte lysates using the mouse thymocyte assay. Interleukin-4 had a clear dose-dependent suppressive effect on the interleukin-1 synthesis. IL-1 alpha and IL-1 beta mRNA levels, quantitated by Northern blot analysis, were equally high in the lipopolysaccharide plus interleukin-4 supplemented cultures and in the cultures with lipopolysaccharide alone, suggesting that the effect of interleukin-4 in the interleukin-1 biosynthesis is post-transcriptional.