Granulocyte-macrophage colony-stimulating factor (GM-CSF): a chemoattractive agent for murine leukocytes in vivo

GM-CSF is well recognized as a proliferative agent for hematopoietic cells and exerts a priming function on neutrophils. The aim of this study was to determine if GM-CSF has a role as a neutrophil chemoattractant in vivo and if it can contribute to recruitment during intestinal inflammation. Initial studies in vitro, using the under-agarose gel assay, determined that GM-CSF can induce neutrophil migration at a much lower molar concentration than the fMLP-like peptide WKYMVm (33.5-134 nM vs. 1-10 mu M). GM-CSF-induced neutrophil migration was ablated (<95%) using neutrophils derived from GMCSFR beta(-/-) mice and significantly attenuated by 42% in PI3K gamma(-/-) neutrophils. In vivo, a significant increase in leukocyte recruitment was observed using intravital microscopy 4 h post-GM-CSF (10 mu g/kg) injection, which was comparable with leukocyte recruitment induced by KC (40 mu g/kg). GM-CSF-induced recruitment was abolished, and KC-induced recruitment was maintained in GMCSFR beta(-/-) mice. Furthermore, in vivo migration of extravascular leukocytes was observed toward a gel containing GM-CSF in WT but not GMCSFR beta(-/-) mice. Finally, in a model of intestinal inflammation (TNBS-induced colitis), colonic neutrophil recruitment, assessed using the MPO assay, was attenuated significantly in anti-GM-CSF-treated mice or GMCSFR beta(-/-) mice. These data demonstrate that GM-CSF is a potent chemoattractant in vitro and can recruit neutrophils from the microvasculature and induce extravascular migration in vivo in a beta subunit-dependent manner. This property of GM-CSF may contribute significantly to recruitment during intestinal inflammation. J. Leukoc. Biol. 89: 945-953; 2011.