Lipopolysaccharide (LPS)-induced IL-6 production by embryonic fibroblasts isolated and cloned from LPS-responsive and LPS-hyporesponsive mice.

Fibroblasts participate in inflammatory processes and non-specific immunity by producing cytokines and mediators in response to bacterial lipopolysaccharide (LPS). The detailed mechanism of LPS-induced cytokine production by fibroblasts has not been sufficiently studied. We isolated murine embryonic fibroblasts (MEF) from LPS-responsive C3H/HeN mice and LPS-hyporesponsive C3H/HeJ mice and established MEF cell lines and MEF clones. Primarily cultured MEF, MEF cell lines and MEF clones from C3H/HeN mice (MEF.He) expressed interleukin (IL)-6 mRNA and produced IL-6 molecules in response to even a very low dose (1 ng/ml) of LPS. By contrast, those from C3H/HeJ mice (MEF.HeJ) neither expressed IL-6 mRNA nor produced IL-6 in response to 1 ng of LPS per ml, although they expressed IL-6 mRNA and produced IL-6 in response to high doses (more than 100 ng/ml) of LPS. The MEF.He clone, but not the MEF.HeJ clone, expressed IL-6 mRNA in response to taxol or ceramide, whereas MEF.HeJ clones as well as the MEF.He clone expressed IL-6 mRNA in response to IL-1alpha. These results indicate that in the responses to LPS, taxol and ceramide, MEF retain the same reactivity as that of the mouse strains from which the MEF were derived, and LPS shares the IL-6 signal transduction pathway with taxol and ceramide, but not with IL-1. CD14 is not relevant to the LPS-induced IL-6 production by MEF, since cloned MEF.He and MEF.HeJ were shown not to express CD14 mRNA by Northern blot analysis. No difference in LPS-specific binding capacity was shown between the MEF.He and MEF.HeJ clones. This finding, together with the fact that hyporesponsiveness of MEF.HeJ to LPS was shown at the level of IL-6 mRNA expression, suggests that the defect in the LPS-induced IL-6 signal transduction pathway in MEF from C3H/HeJ mice is probably located at some site after the LPS-recognition site on the cell surface and before transcription of the IL-6 gene.