Granulocyte-macrophage stimulating factor (GM-CSF) promotes neutrophil(PMN) production and function, and delays the onset of apoptosis in adult PMNs. We have shown that up-regulation of CD11b, an inflammatory adhesion molecule, is diminished in cord blood PMNs following brief stimulation with GM-CSF. To test the hypothesis that differential up-regulation of CD11b might persist with prolonged exposure to GM-CSF, we incubated PMNs from healthy adult donors (n=8) and term cord blood (n=4) in media with GM-CSF. Following incubation (37° C, for 0, 4, 8 h), PMNs were stained with monoclonal anti-CD11b or control IgG, and analyzed by flow cytometry. Surface expression of CD11b (mean channel fluorescence) was similar on freshly-isolated adult and cord blood samples (adult, 436 ± 42; cord blood, 362 ± 48; X± SEM). Chemotactic (10 nM fMLP) up-regulation of CD11b on cultured PMNs was similar between groups at all time points. Data below are shown as PMN surface CD11b levels (percentage of unstimulated values):Table We conclude that prolonged exposure to GM-CSFin vitro preserves CD11b expression on both cord blood and adult PMNs. This study provides further data that therapeutic administration of GM-CSF may promote PMN adhesive function.

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