In response to exogenous as well as endogenous signals, dendritic cells (DC) undergo programmed maturation to become efficient, antigen-presenting cells and mediate innate and adaptive immune responses. Very little is known, however, about the differential maturation responses of canine DC to endogenous and exogenous stimuli, especially the concomitant events related to the specific expression of cytokine genes. Canine monocyte-derived immature DC (iDC) were treated with an exogenous signal, bacterial lipopolysaccharide (LPS), or an endogenous signal, tumor necrosis factor-alpha (TNF-alpha), to generate mature DC (mDC). The mDC generated from either stimuli were characterized by significant increases in the expression of surface molecules, including CD11c, MHC class II, CD80, CD83, and CD86. Using real-time reverse transcriptase polymerase chain reactions, the cytokine expression profiles generated by these two stimuli were studied. Compared with the iDC, the LPS-stimulated mDC exhibited a significantly increased expression of IL-1 beta, IL-10, IL-12p40, IL-13, and TNF-alpha. Using the mixed lymphocyte reaction and cytokine intracellular staining, it was shown that the array of cytokines from LPS-generated mDC contributed to T cell priming and T helper cell type 1 (Th1) polarization. TNF-alpha-generated mDC increased the expression of a distinctly different panel of cytokines, namely IL-2, IL-4, IL-12p40, IL-13, TNF-alpha, TGF-beta, IFN-gamma, and MCP-2, and shifted naïve T cell differentiation to T helper cell type 2 (Th2) polarization. IL-13 expression was dramatically increased in canine TNF-alpha-generated mDC, which does not occur in other mammalian species, including humans. Because IL-13 is functionally similar to IL-4, IL-13 may contribute to the observed Th2 polarization. Thus, canine DC maturing from different stimuli release different cytokine profiles that in turn promote different immune responses and activate innate and adaptive immune responses.