Hepatocyte and immune system: acute phase reaction as a contribution to early defence mechanisms.

Cytokines, a variety of hormone-like molecules, include a group of soluble factors the interferons, interleukins, and hematopoietic growth factors. They build a complex network of interactive signals and are important for the regulation of hematopoesis and many immune reactions. The interaction of the hepatocyte with the immune system may occur at different levels (Fig 1). For example viral infections often induce interferon (IFN) production, but can also stimulate synthesis of class II molecules, tumour necrosis factor and interleukin (IL) 2.1 2 IFN activates other cytokines directly by interacting with IFN sequence motifs in their promotors.3 Little information exists on the role of cytokines in the initiation and perpetuation of liver diseases. The level and activity of different cytokines such as IL 6 can be abnormal and may contribute to the injury in immunologically mediated liver diseases.4 Another mechanism is the 'acute phase response', in which a panel of cytokines regulates different liver specific genes. There is detailed knowledge on how the signals of these cytokines are transduced from the surface of the hepatocyte membrane to the promotor of the liver specific gene: the mechanisms will be reviewed in this article.