Dissociation between interleukin-1 beta mRNA and protein synthesis in human peripheral blood mononuclear cells

Human peripheral blood mononuclear cells analyzed immediately after isolation did not express detectable mRNA for interleukin-1 beta (IL-1 beta). In the strict absence of lipopolysaccharide (LPS), incubation in glass or plastic resulted in expression of IL-1 beta mRNA without detectable IL-1 beta synthesis, even when cells were incubated for 20 h. The accumulation of IL-1 beta mRNA was most likely due to adherence since rotating the containers reduced the amount of mRNA. However, the cells were "primed" by 3 h adherence since subsequent stimulation with LPS resulted in more IL-1 beta (214%) 4 h after stimulation compared to freshly obtained, LPS-stimulated cells. Ratios of IL-1 beta mRNA induced by LPS versus adherence were 7.8, 36, and 20 at 4, 12, and 24 h, respectively; the corresponding ratios for IL-1 beta protein were 18, 160, and 180. Comparing Staphylococcus epidermidis versus LPS, the ratios of IL-1 beta mRNA were 3.2, 0.5, and 1.2 at 4, 8, and 24 h, respectively, however, the corresponding ratios for IL-1 beta protein were 65, 22, and 10. The differences in transcription versus translation in these studies are unlikely due to changes in stability of mRNA since the half-life of adherence-induced IL-1 beta mRNA was 2.5 versus 4 h for LPS-induced mRNA. There was also no evidence of superinduction of mRNA in peripheral blood mononuclear cells stimulated with LPS, whereas, tumor necrosis factor alpha mRNA was elevated in the presence of cycloheximide. Using different methods of cell surface stimulation, our results demonstrate that synthesis of IL-1 beta is regulated by at least two separate mechanisms, one at the level of transcriptional activation and the other one involving translational efficiency.