The effects of GM-CSF on myeloperoxidase release in normal and myelodysplastic neutrophils

When purified control neutrophils were primed with GM-CSF, a significant increase in FMLP-induced MPO release was observed (mean ± S.E.M., 3.4 ± 0.8 mU/10 7 unprimed cells compared to 6.5 ± 1.1 mU/10 7 primed cells, p < 0.001). This MPO release was greatly augmented by Cytochalasin B (Cy B), but after the addition of Cy B the priming effects of GM-CSF became less obvious. Exposure to GM-CSF without FMLP did not enhance MPO release. Within whole blood, FMLP produced negligible MPO release, but priming with GM-CSF prior to FMLP always resulted in a significant increase in MPO release. Myelodysplastic neutrophils released similar amounts of MPO in response to FMLP, compared with control cells (3.4 ± 0.8 mU/10 7 control cells compared to 2.7 ± 0.3 mU/10 7 MDS cells, p > 0.05). Priming with GM-CSF produced an increase in FMLP-stimulated MPO release comparable with control cells. In terms of total MPO content, although some MDS patients exhibited low levels, as a group there was no significant difference from controls (169 ± 21 mU/10 7 control cells compared with 57 ± 19 mU/10 7 MDS cells). These findings suggest that MPO activity is not a universal defect in MDS and cannot account for the defects in respiratory burst activity in these neutrophils.