pDCs promote the proliferation of both naive and memory B cells, although Ig secretion is restricted to the memory subset. Total B cells or B cells sorted into naive and memory subsets based on CD27 expression were cultured with resting or CpG-B-pDCs. (A) Proliferation was assessed by analyzing CFSE dilution on day 5. The shaded histogram represents B cells cultured with CD40L; dashed histogram, B cells cultured with resting pDCs; and solid histogram, B cells cultured with CpG-B-pDCs. Results of 1 donor representative of 3 are shown. (B) Supernatant was collected on day 14, and IgG and IgM levels were determined by ELISA. Mean results ± SEM from 1 experiment representative of 3 are presented. Data were analyzed by unpaired t test: *P < .05 and ***P < .001.