The action of interleukin 6 and leukaemia inhibitory factor on liver cells.

The hepatic action of cytokines has generally been analysed in terms of the acute-phase response of the liver. The qualitative and quantitative changes in the expression of plasma proteins serve as defining criteria for cytokine function. Interleukin 6 (IL-6) and leukaemia inhibitory factor (LIF) are representatives of a group of cytokines which display strikingly similar effects in both human and rodent liver cells. Hallmarks of the action of these cytokines are the stimulation of type 2 acute-phase plasma proteins and enhancement of the effect of interleukin 1 (IL-1) or tumour necrosis factor alpha (TNF-alpha) on type 1 acute-phase plasma proteins. The transcriptional activation of the various acute-phase plasma protein genes involves common cis-acting regulatory elements whose sequences and location relative to the transcription start site vary from gene to gene. The activity of the IL-6- and LIF-responsive genes depends in part on transcription factors including several members of the C/EBP family, JunB and the glucocorticoid receptor. The expression of these transcription factors is in turn under cytokine-specific control. In a few cases, expression is temporally correlated with the activation of 'late' acute-phase protein genes. The finding that structurally distinct cytokines interact with separate receptors but elicit an almost identical liver cell response demands a reassessment of the contribution of each factor to the in vivo acute-phase response.