IL-12 responsiveness and expression of IL-12 receptor in human peripheral blood monocyte-derived dendritic cells

We analyzed the expression of IL-12R beta 1 and IL-12R beta 2 and the role of IL-12 in the activation of monocyte-derived dendritic cells (DCs) via IL-12R beta 1-mediated signaling events. Flow cytometric analysis revealed that IL-12R beta 1 was expressed in T cells, Con A blasts, and monocyte-derived DCs, but not in monocytes, while its transcript was detected in all of these cell types. Transcriptional expression of IL-12R beta 2 was observed in T cells, Con A blasts, and monocyte-derived DCs, but not monocytes, The ligation of DCs as web as Con A blasts by IL-12 induced the production of GM-CSF, IL-1 beta, IL-6, TNF-alpha, and IFN-gamma at the transcription levels. Furthermore, stimulation of DCs with IL-12 induced IL-12p40 transcript, but not IL-12p35 transcript, whereas this stimulation caused the expressions of both transcripts in Con A blasts. Stimulation of DCs with IL-12 caused a tyrosine phosphorylation of several intracellular proteins, and the pattern of these events were distinct from those of IL-12-stimulated Con A blasts. IL-12 also induced tyrosine phosphorylation of IL-12R beta 1 as well as recruitment of several tyrosine-phosphorylated proteins to IL-12R beta 1 in DCs and Con A blasts. Receptor engagement of DCs as well as Con A blasts by IL-12 resulted in activation of Janus kinase 2 and Tyk2 kinases and Stat3 and Stat4 transcription factors and the association of these proteins to IL-12R beta 1, Stimulation with IL-12 caused a tyrosine phosphorylation and enzymatic activity of a family of mitogen-activated protein kinases, p38(mapk). These results suggest that IL-12 acts directly on DCs to induce their functional activation via IL-12R beta 1-mediated signaling events.