Differentiation of DCs derived from CD34⁺ cells is inhibited by IL-6.

CD34⁺ progenitor cells were incubated with GM-CSF, TNF-α, SCF, and FLT3-L (G+T+S+F) with or without IL-6. Medium with cytokines was replaced at day +7 with IL-4 used in place of the early-acting growth factors SCF and FLT3-L to stimulate terminal differentiation of DCs. At day +14, the cells were labeled with CD14-PE/CD1a-FITC, HLA-DR-PE/CD40-FITC, or CD86-PE/CD80-FITC and were analyzed on a FACScan (A). (B) Antibodies to anti–IL-6 were used to neutralize the inhibitory effect of the cytokine. Results are from one representative experiment of 5 different samples analyzed. IL-6 up-regulated CD14 and down-regulated CD1a, HLA-DR, CD40, and CD80 antigens (A). The effects of IL-6 on CD14/CD1a phenotype were reversed by anti–IL-6 neutralizing antibodies (B).