Treatment of average-risk acute lymphoblastic leukaemia (ALL) in children consists of 6 months of intensive chemotherapy followed by 18 months of maintenance therapy. Polymorphonuclear leucocyte (PMN) functions from children with ALL were studied in order to evaluate and compare the toxicity of the initial intensive treatment with the toxicity of the subsequent less intensive maintenance treatment. H2O2 and O2- production, evaluated by chemiluminescence, were significantly decreased during the intensive period but returned to normal values when maintenance therapy began. In contrast, bactericidal activity against Gram-positive and Gram-negative microorganisms remained at low levels throughout the treatment but returned to normal values in patients off chemotherapy. PMN from patients on maintenance therapy exhibited an excess of morphological changes associated with apoptosis. This was confirmed by standard two-colour flow cytometry which revealed an increase in the number of hypodiploid cells, and increased expression of membrane phosphatidylserine together with a drastic reduction in the expression of the Fcgamma receptor IIIB (CD16). These defective PMN were differentially sensitive to the effects of granulocyte colony stimulating factor (G-CSF): G-CSF induced similar increase in chemiluminescence in control and patient PMN; GSF partially corrected the defective bactericidal activity; G-CSF did not affect the accelerated PMN apoptosis. These observations indicate that ALL children undergoing chemotherapy present PMN defective functions which are partially sensitive or even resistant to G-CSF. ; Journal Article ; SCOPUS: ar.j ; info:eu-repo/semantics/published