B cells were obtained from buffy coats prepared from the peripheral blood of adults (Sanquin, Amsterdam, Netherlands) by Ficoll separation and CD19 MACS microbeads as described by the manufacturer (Miltenyi Biotech). CD19 MACS-selected B cells were subsequent sorted for CD3 neg CD19 pos CD27 pos , CD3 neg CD19 pos CD27 pos sIgG pos or CD3 neg CD19 pos CD27 pos TT pos .