During an immune response, antigen-bearing dendritic cells (DCs) migrate to the local draining lymph node and present antigen to CD4+helper T cells. Antigen-activated CD4+T cells then up-regulate TNF superfamily members including CD40 ligand and lymphotoxin (LT)αβ. Although it is well-accepted that CD40 stimulation on DCs is required for DC licensing and cross-priming of CD8+T-cell responses, it is likely that other signals are integrated into a comprehensive DC activation program. Here we show that a cognate interaction between LTαβ on CD4+helper T cells and LTβ receptor on DCs results in unique signals that are necessary for optimal CD8+T-cell expansion via a type I IFN-dependent mechanism. In contrast, CD40 signaling appears to be more critical for CD8+T-cell IFNγ production. Therefore, different TNF family members provide integrative signals that shape the licensing potential of antigen-presenting DCs.