Class R and B inhibitory oligonucleotides (INH-ODNs) have similar inhibitory potencies for Toll-like receptor-9 (TLR9)-activated primary macrophages and dendritic cells (DCs). (a) Enriched primary macrophages were stimulated with class A(D) CpG-ODN (100 nM) for 18 to 24 hours. INH-ODNs were added over the concentration range shown. Interleukin (IL)-12p40 and tumor necrosis factor-alpha (TNF-α) were measured in enzyme-linked immunosorbent assay (ELISA). Flt-3-propagated bone marrow-derived DCs were stimulated for 24 hours either with class A(D) CpG-ODN 2336 or CG50+PA4 immune complexes or with various combinations of TLR9 ligands and class R or class B INH-ODNs or control ODNs. INH-ODNs and control ODNs were used either at a concentration of 1 μg/mL (b-d) or over the concentration range shown (e). Interferon-alpha (IFN-α) secretion was measured in ELISA (n = 3 to 5). *P < 0.05.