The effective maturation of dendritic cells (DC) is complex and highly regulated and requires the presence of a variety of signals. Tumor necrosis factor (TNF) and its receptors or innate pattern recognition receptors such as the toll-like receptors have been shown to contribute to this process. DC derived from bone marrow cells in the presence of granulocyte/macrophage colony-stimulating factor can be used as a model to ascertain the contribution of different signals to DC maturation. Analysis of DC activated by addition of the mycobacterial vaccine strain Bacillus Calmette-Gue rin showed that of the effector molecules studied only interleukin-10 expression was significantly reduced in TNF-negative (B6.TNF-/-) DC. Another effector molecule produced by DC, inducible nitric oxide synthase, was largely unchanged.