Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) Augments Acute Lung Injury via Its Neutrophil Priming Effects

Granulocyte macrophage-colony stimulating factor (GM-CSF) has immuno-stimulatory effects. We hypothesized that GM-CSF plays an important role both in lipopolysaccharide (LPS)- and hemorrhage-induced acute lung injury (ALI). We also postulated that GM-CSF augments LPS-induced inflammation by priming neutrophils. ALI was induced in GM-CSF-/- or control C57BL mice either by LPS injection or by hemorrhage. Lung inflammation (by lung expression for tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2), interleukin-1β (IL-1β), interleukin-6 (IL-6), and keratinocyte-derived chemokine) and lung injury (by myeloperoxidase and evans blue dye assay) were evaluated after ALI. Incremental doses of LPS (0, 1, 10, and 100 ng/mL) and GM-CSF (0, 1, 10, and 100 ng/mL) were added to bone marrow neutrophils. The expression of TNF-α, MIP-2, and IL-1β was evaluated with enzyme linked immunosorbent assay. The mRNA expression of three cytokines, and the nuclear translocation of nuclear factor kappa B (NFκ-B) were evaluated by reverse transcriptase-polymerase chain reaction and electropnoretic mobility shift assay, respectively. GM-CSF -/- mice showed decreased neutrophil infiltration, less leakage, and lower expression of cytokines in the lung after LPS or hemorrhage. GM-CSF augmented LPS-induced protein and mRNA expression of TNF-α, MIP-2 and IL-1β, which was mediated by increased intra-nuclear translocation of NF-κB. GM-CSF plays an important role in high-dose LPS and hemorrhage-induced ALI, which appears to be mediated by its priming effect on neutrophils.