Involvement of MSC-derived PGE₂ in the inhibition of DC differentiation: analysis of CD1a and CD14 surface expression. Purified CD14⁺ cells were cultured with GM-CSF and IL-4 to induce differentiation into DCs. Cultures were performed either in the absence (■) or in the presence (▧) of MSCs. In addition, the PGE₂ inhibitor NS-398 (5 μM) was added to monocyte-MSC cocultures () or 1 μM PGE₂ was added to monocytes cultured alone (). After 5 days, phenotypic analysis was performed to check DC differentiation. (A) A representative experiment. Numbers represent percentages of positive cells. (B) Expression of CD14 and CD1a in cells cultured under the described culture conditions. Results are expressed as mean ± SD of the percentages of marker-positive cells obtained from the analysis of 11 independent experiments performed. ***P < .001.