TLR stimulation directly inhibits DC development. (A) Bone marrow cells from either TLR9^–/– or wt (C57BL/6) mice were differentiated with GM-CSF in the absence or presence of LPS or CpG-ODN. Cells from the different mice were either combined in a transwell format (left) or incubated alone (right). Cells were analyzed at day 9 for CD11c expression by FACS. (B) Experiments were done as above with C3H/HeJ (LPS-unresponsive) and C3H/HeN (control) mice (mean + SD; n = 4, *P < .05 against the respective control stimulation).