Bacterial lipopolysaccharide, TNF-alpha, and calcium ionophore under serum-free conditions promote rapid dendritic cell-like differentiation in CD14(+) monocytes through distinct pathways that activate NF-kappa B

To facilitate the study of signaling pathways involved in myeloid dendritic cell (DC) differentiation, we have developed a serum-free culture system i n which human CD14(+) peripheral blood monocytes differentiate rapidly in r esponse to bacterial LPS, TNF-alpha, or calcium ionophore (CI), Within 48-9 6 h, depending on the inducing agent, the cells acquire many immunophenotyp ical, morphological, functional, and molecular properties of DC. However, t here are significant differences in the signaling pathways used by these ag ents, because 1) LPS-induced, but not CI-induced, DC differentiation requir ed TNF-alpha production; and 2) cyclosporin A inhibited differentiation ind uced by CI, but not that induced by LPS, Nevertheless, all three inducing a gents activated members of the NF-kappa B family of transcription factors, including Rein, suggesting that despite differences in upstream elements, t he signaling pathways all involve NF-kappa B, In this report we also demons trate and offer an explanation for two observed forms of the RelB protein a nd show that RelB can be induced in myeloid cells, either directly or indir ectly, through a calcium-dependent and cyclosporin A-sensitive pathway.