Blood monocytes (MN) were prepared from cytapheresis samples obtained from healthy blood donors with no previous history of malaria (Lecourbe Blood Bank, Paris, France). Peripheral blood mononuclear cells (PBMC) were separated on Ficoll density gradients J PREP (TechGen, Les Ulis, France) and washed in Ca 2+ and Mg 2+ free HBSS buffered with 10 mM HEPES (both from GibcoBRL-Invitrogen). Cells were then distributed on polystyrene 96-well flat-bottomed culture plates (TPP, Trasadingen, Switzerland) and adherent MN were selected by incubation for 2 h at 37uC, in a humidified 5% CO 2 atmosphere. More than 90% of the adherent cells obtained in this manner were MN as estimated by the non-specific esterase test (a-naphtyl acetate esterase; Sigma). MN from each donor were tested prior to ADCI assays and only those without direct inhibitory effect were used in assays.