BCR-mediated uptake of particulate Ag-CpG gives rise to B-cell proliferation and PC differentiation in vitro. (A,B) CFSE-labeled B cells were stimulated with 1 μL particulate HEL alone, particulate CpG alone, or particulate HEL-CpG for 72 hours. (A) Flow cytometry was used to measure proliferation by CFSE dilution (top panel) and CD138 up-regulation (bottom panel) in stimulated (black line) and unstimulated (gray filled) MD4 B cells; (B) IL-6 (left panel) and IgM^a (right panel) secretion by WT and MD4 B cells were determined by ELISA. (C) MD4 B cells expressing the chimeric BCRs IgM/β or IgM/β^Y<L were stimulated with 1 μL particulate HEL alone, particulate CpG alone, or particulate HEL-CpG for 72 hours. IL-6 (left panel) and IgM^a (right panel) secretion were determined by ELISA. (D) MD4 B cells were stimulated with either a mixture of 1 μL particulate CpG and 5 μg soluble anti-IgM (αIgM + CpG) or 1 μL particulate HEL-CpG (HEL-CpG) for 72 hours. IL-6 (left panel) and IgM^a (right panel) secretion were determined by ELISA. Values represent the mean (± SD) from triplicate samples.