Amount of CpG present on the Ag-containing particulates modulates the extent of B-cell proliferation and differentiation to form PCs in vitro. (A,B) CFSE-labeled B cells were stimulated with 1 μL particulate HEL conjugated with various densities of CpG. The density of CpG is represented from highest to lowest on moving from left to right. Proliferation and differentiation of MD4 B cells were measured 72 hours after stimulation. (A) Flow cytometry was used to measure CFSE dilution in stimulated (black line) and unstimulated (filled gray) MD4 cells. (B) IL-6 (left panel) and IgM^a (right panel) secretion were assessed by ELISA.