Stimulation of naive mouse dendritic cells (DC) with LPS or Pam 3 CSK 4 (P3C) induces production of TNF-α via TLR4-or TLR2-signaling. Although tolerance in macrophages has been studied in detail, we investigated the role of TLR agonist concentration and IL-6 for tolerance in DC. P3C-or LPS-primed DC were nonresponsive to P3C or LPS restimulation in terms of TNF-α but not IL-6 production. The mechanisms involved in tolerance were dependent on the concentration of the TLR ligand used for DC priming. DC primed with LPS or P3C at high concentrations developed a maturation dependent, IL-6 independent tolerance associated with inhibition of TLR signaling upstream of IκB as indicated by decreased IκB degradation. In contrast, priming of DC with LPS or P3C at low concentrations resulted in IL-6-dependent tolerance, which was abolished in IL-6 deficient DC, and was not accompanied by maturation of DC or by down-regulation of TLR2 or TLR4. In homotolerogenic DC primed with LPS or P3C at high concentrations, degradation of IκB upon restimulation with LPS or P3C was inhibited suggesting tolerance mechanism (s) upstream of IκB; in contrast, cross-tolerance in DC primed with LPS or P3C at low concentrations was not associated with reduced IκB degradation suggesting tolerance mechanisms downstream of IκB. Our data indicate that in naive DC TLR4-and TLR2-stimulation results in homo-and cross-tolerance; the mechanisms involved in tolerance depend on the concentration of the TLR agonist used for DC priming and are governed by IL-6 and maturation.