Bacterial sepsis accounts for as many as 15% of neonatal deaths in the United States. A decrease in both neutrophil number and function plays a role in reduced neonatal host defense. Host defense actions that are diminished in the neonate closely mimic the actions of granulocyte colony stimulating factor(G-CSF), a cytokine that acts on progenitor cells by stimulating clonal proliferation of neutrophils. In addition, G-CSF stimulates increased surface adhesion molecules and neutrophil chemotactic receptor expression. The effects of G-CSF on neonatal neutrophil adhesive molecules such as L-selectin andβ2-integrin are not well defined. We therefore evaluated the effects of G-CSF on neonatal neutrophil adhesive phenotypes. Whole cord blood was incubated with either G-CSF (10 ng/mL) or sterile filtered PBS for one hour at 37°C. Following N-formyl-methionyl-phenyalinine (FMLP) stimulation, samples were incubated with fluorescent-labeled mouse monoclonal antibodies to L-selectin (PE-CD62) and β2-integrin (FITC-CD11b) at 4°C for one hour, then evaluated by flow cytometry. Calibration beads were used to calculate the total number of binding sites. In both term (n=6) and preterm(n=6) cord blood neutrophils, G-CSF incubation increased β2-integrin expression significantly over baseline (term, 180±15%, preterm, 155±16%, p<0.01) compared to PBS incubation, which did not alterβ2-integrin expression. Following FMLP stimulation, β2-integrin expression increased even more in the G-CSF stimulated group (term, 284±27%, preterm, 233±22%), and was significantly greater than the PBS stimulated group (term, 212±18%, preterm, 185±18). Neutrophils decreased the number of L-selectin binding sites to 77±10%(term) and 88±9% (preterm) of baseline values following G-CSF incubation, and L-selectin shedding was even greater following FMLP stimulation in the G-CSF group compared to the PBS group (term, 52±7% versus 71±7%, p<0.05; preterm 53±6 versus 67±7%, p<0.01). We speculate that G-CSF administration will improve the adhesive function of neonatal neutrophils by priming cells prior to infectious exposure, thereby improving neonatal host defense.