HL-60 cells.

HL-60 cells, a human promyelocytic leukemia line, were obtained from the ATCC, Manassas, VA, and were maintained in Dulbecco's modified Eagle's medium (DMEM)–F-12 with 18 mM NaHCO₃ and 7.5% fetal bovine serum. The HL-60 cells were induced to differentiate into neutrophil-like cells by treatment with 1.1% dimethyl sulfoxide (DMSO) plus 10 μM all-trans-retinoic acid (ATRA) for 48 h. For some experiments testing chemotaxis or ATP release, HL-60 cells were used without chemically induced differentiation.