Endotoxin down-regulates monocyte and granulocyte interleukin-6 receptors without influencing gp130 expression in humans

Interleukin (IL)-6 is important for host defense against various pathogens. The IL-6 receptor (IL-6R) complex consists of a ligand-binding component ( IL-6R) and a signal-transducing component (gp130), In a study designed to o btain insight into the regulation of this receptor complex during inflammat ion, 8 healthy subjects received an intravenous injection of lipopolysaccha ride (LPS; 4 ng/kg), and receptor expression was determined on blood leukoc ytes by use of fluorescence-activated cell cytometry. LPS induced a transie nt decrease in monocyte and granulocyte IL-6R expression but did not influe nce gp130. The plasma concentrations of soluble IL-6R and soluble gp130 did not change after LPS administration. Expression of the receptor for leukem ia inhibitory factor, a member of the IL-6R family, remained unaltered afte r LPS injection. In whole blood in vitro, LPS and gram-positive stimuli and proinflammatory cytokines were capable of down-modulating the IL-6R. Monoc ytes and granulocytes may down-regulate IL-6R at their surface upon their f irst interaction with bacterial antigens.