Endotoxin Down-Modulates Granulocyte Colony-Stimulating Factor Receptor (CD114) on Human Neutrophils

During infection, the development of nonresponsiveness to granulocyte colony-stimulating factor (G-CSF) may be influenced by the down-modulation of G-CSF receptor (G-CSFR) by cytokines. This down-modulation was studied during experimental human endotoxemia. Healthy volunteers received either 2 ng/kg endotoxin (lipopolysaccharide [LPS], n = 20) or placebo (n = 10) in a randomized, controlled trial. Endotoxin infusion increased the mean fluorescence intensity of the neutrophil activation marker CD11b >300% after 1 h (P <.001 vs. placebo). LPS infusion down-modulated G-CSFR expression in as early as 60 min (-17%; P =.001 vs. placebo). Down-modulation was almost maximal at 90 min and persisted for 6 h (-50% from baseline; P <.0001 vs. placebo). Plasma levels of G-CSF started to increase only after G-CSFR down-modulation had occurred and peaked 37-fold above baseline at 4 h (P <.0001 vs. placebo). In conclusion, LPS down-modulates G-CSFR expression in humans, which may render neutrophils less responsive to the effects of G-CSF and, thereby, compromise host defense mechanisms.