Induction of interleukin 6 by human and murine recombinant interleukin 1 in mice

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Abstract
Interleukin (IL) 6 is a pleistropic cytokine with activities, among others, on immune cells, hematopoietic precursor cells and hepatocytes. We have investigated the kinetics and amplitude of its in vivo induction in mice after injection of four different IL 1 species as well as murine (m) and human (h) tumor necrosis factor (TNF) and bacterial lipopolysaccharide (LPS) using a sensitive bioassay on 7TD1 cells to measure the IL 6 concentrations. Recombinant mIL 1β, administered as a single i.v. injection in mice, induced the appearance of IL 6 in the plasma with peak levels observed after 2 h. A dose‐response correlation was found between serum IL 6 levels and injected IL 1α concentrations at 3 and 8 h after the injection. We then compared the ability of h/mIL 1α, h/mIL 1β, h/mTNF and LPS to induce IL 6 in mice. We found: (a) LPS is the most potent inducer of IL 6; (b) 3 h after injection, the four IL 1 preparations had induced IL 6 levels comparable with the IL 6 levels observed after TNF injection; (c) high doses of mIL 1, α or β, but not hIL 1, resulted in a high IL 6 level persisting for over 8 h. We conclude that IL 1 is a potent inducer of IL 6 in vivo and that no major differences are observed between the four IL 1 preparations, as evaluated at 3 h after the injection. However, mIL 1α and mIL 1β, in contrast to hIL 1α and hIL 1β, induced a sustained IL 6 level over a longer time period. This pattern of prolonged IL 6 induction is even much more pronounced after mTNF injection, but not after hTNF injection.