Signaling through toll-like receptors (TLRs) is essential for dendritic cell (DC) maturation induced by bacteria and other pathogens. The mechanism for virus-induced DC maturation is not known. By use of pairs of live viruses with different abilities to induce the interferon (IFN) pathway, a strong correlation between DC maturation and the ability of the virus to induce type I IFN synthesis was demonstrated. The secreted IFN was not necessary, nor was it sufficient to induce full DC maturation. Intracellular viral replication is necessary for this process, and the transcription factor nuclear factor-κB was crucial for cytokine induction. The double-stranded RNA-dependent protein kinase was not essential for DC maturation. Similar to TLR-induced DC maturation, after virus infection, separate pathways for the induction of cytokine secretion and the upregulation of major histocompatibility complex and costimulatory molecules were activated. It was demonstrated that these pathways have different sensitivities to the presence of viral stimulus.