Effect of granulocyte-macrophage colony-stimulating factor on chemiluminescence of human neutrophils

We investigated the capacity of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) to enhance the function of neutrophils. Neutrophil function was measured in terms of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced luminol-dependent chemiluminescence (LDCL). LDCL of fMLP-stimulated neutrophils was enhanced up to 4.5 fold following preincubation with rhGM-CSF. This enhancement depended on the length of preincubation, reaching an optimal level at 120 min. The dose-response relationship for fMLP-induced LDCL of neutrophils preincubated with rhGM-CSF revealed that half-maximum enhancement was achieved at an approximately 20-fold higher concentration than that of colony-forming units in culture-derived colony formation. These results suggest that differences in dose dependency may be explained by differences in the distribution of receptor(s) for GM-CSF. This may also enable GM-CSF to affect the hematopoietic system, which contains cells at various levels of differentiation, thus mediating the host-defense mechanism.