Actin polymerization in neutrophils from patients affected by myelodysplastic syndromes--a flow cytometric study.

In this study F-actin polymerization in neutrophils from 21 patients affected by myelodysplastic syndromes (MDS) was evaluated by means of a flow cytometric assay. Neutrophils were stimulated with formyl-methionyl-leucyl-phenylanaline (fMLP; 10(-8) M final concentration) for 15, 30, 60 and 120 sec, and F-actin content was determined using fluorescein-isothiocyanate phallacidin as a specific probe. Eight normal subjects were studied as controls. We found that F-actin polymerization was defective in ten patients, with very impaired values after 60 and 120 sec of stimulation with fMLP. The remaining 11 patients showed a prevalent neutrophil population with normal F-actin polymerization and neutrophil sub-populations with either defective or undetectable F-actin polymerization. In the first group, patients with very poor prognosis (refractory anemia with excess blasts, refractory anemia with excess blasts in leukemic transformation, trisomy 8, multiple karyotypic abnormalities) were present, although patients with aberrations of karyotype were present in the second group. It is possible that defects in neutrophil F-actin polymerization may be responsible for neutrophil dysfunction, which has frequently been observed in MDS.