A simple bioassay for monocyte-derived hepatocyte stimulating factor: increased synthesis of alpha 2-macroglobulin and reduced synthesis of albumin by cultured rat hepatocytes.

Cytokines released from monocytes upon stimulation by lipopolysaccharide cause a number of cells to undergo proliferative and synthetic changes. At least one of these cytokines affects hepatocytes in vivo causing increased synthesis of a series of acute-phase proteins. We have established an in vitro micro-assay for hepatocyte stimulating factor (HSF) using primary cultures of normal rat hepatocytes. Measurement of increased synthesis of alpha 2-macroglobulin and decreased synthesis of albumin caused by exogenously added factor constitute a sensitive parameter for quantifying HSF. For comparing various cytokines preparations, we have defined a unit of HSF activity in terms of a stimulation index. We have used this assay to follow some preliminary attempts to isolate the factors responsible for stimulation of synthesis of acute-phase reactant by the liver.