Peripheral blood mononuclear cells (PBMC) from P. falciparum-exposed, recently pregnant multiparous women were isolated and cryopreserved as described (Hviid et al., 1993) . At the day of use, PBMC were thawed and IgG + memory B cells were isolated using CD22 microbeads (Miltenyi) followed by cell sorting as described (Traggiai et al., 2004) . Cells were immortalized at 100 cells per well in multiple 96-well plates using EBV in the presence of CpG ODN2006 (Microsynth, Switzerland) (Hartmann and Krieg, 2000) and irradiated PBMC as described (Traggiai et al., 2004) .