Monocyte-derived macrophages, but not monocytes nor monocyte-derived DCs, respond to IL-29 because of the restricted IL-28RA expression by monocyte-derived macrophages. (A) Monocytes, monocyte-derived DCs, and monocyte-derived macrophages were pretreated with IL-29 for 5 hours, and then further stimulated with LPS or R848 for 24 hours. TNF production was determined by ELISA. The values depicted show representative data from 11 independent experiments. (B) Monocytes, monocyte-derived DCs, and monocyte-derived macrophages were stained with antibodies against IL-28RA and IL-10R2 to evaluate the expression of the IFNλ receptor by flow cytometry. The specificity of the staining was controlled with the appropriate isotype antibodies. The histograms depicted show representative data from 10 independent experiments. (C) Monocytes, monocyte-derived DCs, and monocyte-derived macrophages were stimulated with IL-29 or IFNα for 20 minutes, and then cells were fixed and permeabilized. The phosphorylation of STAT-1 was measured by flow cytometry (FACSCanto II; BD Biosciences).