B-cell proliferation and differentiation in response to particulate Ag-CpG is dependent on stimulation of TLR9 in vitro. (A,B) MD4 and (A) MD4 TLR9^−/− or (B) MD4 MyD88^−/− B cells were stimulated with 1 μL particulate HEL alone, particulate CpG alone or particulate HEL-CpG for 72 hours. IL-6 (left panels) and IgM^a (right panels) secretion were determined by ELISA. Values represent the mean (± SD) from triplicate samples.