IL-6 functions as an exocrine hormone in inflammation. Hepatocytes undergoing acute phase responses require exogenous IL-6.
We have previously shown that IL-6 is the major monocyte- and fibroblast-derived regulator of acute phase protein gene expression and synthesis in hepatocytes in inflammation. Recently, we and others have shown that rat and human hepatoma cells express IL-6 mRNA, and the question arose as to whether normal hepatocytes express IL-6 and whether any such expression occurs under normal physiologic conditions or is seen in inflammation. Poly A+ mRNA of liver from normal rats and from rats undergoing an acute phase response was not positive when probed with cDNA for rat IL-6 under conditions in which macrophage mRNA was strongly positive. We then compared poly A+ mRNA from purified hepatocytes freshly isolated from normal rats--from rats that were undergoing an acute inflammatory response and from freshly isolated normal hepatocytes that had been cultured for 24 h in the presence or absence of dexamethasone (microM). Only the mRNA from normal hepatocytes cultured for 24 h in the absence of any glucocorticoid was obviously positive for IL-6. The increased expression of gamma-fibrinogen mRNA indicated the presence of inflammation. These results confirm the identification of IL-6 as an exogenous hormone for regulating normal hepatic acute phase protein synthesis in inflammation and rules out an autocrine mechanism being active in the liver in normal homeostasis.
Gauldie
J
J
Department of Pathology, McMaster University, Hamilton, Canada.
Northemann
W
W
Fey
G H
GH
D000210:Acute-Phase Reaction / Q000503:physiopathology*; D000818:Animals; D015152:Blotting, Northern; D015870:Gene Expression; D007249:Inflammation / Q000503:physiopathology*; D015850:Interleukin-6 / Q000502:physiology*; D008099:Liver / Q000503:physiopathology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011919:Rats, Inbred Strains
D015850:Interleukin-6; D012333:RNA, Messenger