induction of interleukin 6 by human and murine recombinant interleukin 1 in mice 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 1 beta administered as a single iv injection in mice induced the appearance of il 6 in the plasma with peak levels observed after 2 h a doseresponse correlation was found between serum il 6 levels and injected il 1 alpha concentrations at 3 and 8 h after the injection we then compared the ability of hmil 1 alpha hmil 1 beta hmtnf 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 alpha or beta 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 1 alpha and mil 1 beta in contrast to hil 1 alpha and hil 1 beta 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