Leukaemia inhibitory factor and interleukin 6 are expressed at very low levels in the normal adult mouse and are induced by inflammation.

We have assessed the limitations of the polymerase chain reaction (PCR) as a semiquantitative technique for assessing very low level gene expression. Using PCR, the in vivo expression patterns of the cytokines Leukaemia Inhibitory Factor (LIF) and Interleukin 6 (IL-6) in the normal adult mouse, have been examined. We show that both LIF and IL-6 mRNA are constitutively expressed, albeit at extremely low levels, in most tissues. While it is unclear whether this low level of expression is of biological significance, it is possible that it reflects a local mode of action of these potent polyfunctional molecules. Lipopolysaccharide, the bacterial cell wall product responsible for endotoxic shock, when administered in vivo, was capable of inducing the expression of both LIF and IL-6 in all of the tissues examined. In addition, LIF and IL-6 expression was induced in lung tissue by in vitro culturing in serum-free media. This induction of LIF and IL-6, by LPS and culturing, may reflect the role of these molecules as mediators of the acute phase response to tissue damage.