Human dendritic cells express the thrombopoietin receptor, c-Mpl

Human thrombopoietin (TPO) is a haemopoietic growth factor that is essentia l for the growth and development of megakaryocytes. However, c-Mpl. the TPO receptor, has been detected in human leukaemic cell lines with a myelomono cytic phenotype, These results raise the possibility that dendritic cells ( DC), a putative myeloid lineage cell, may also express c-Mpl and respond to TPO. In haemopoietic stem cell transplantation, DC could induce graft-vers us-host disease by its strong antigen-presenting capacity In this study we have examined the effect of TPO on differentiation and the antigen-presenti ng capacity of DC. To differentiate DC, cord blood CD34(+) cells were cultu red in the presence of a cytokine cocktail either in serum-free medium or R PMI1640 containing 10% fetal bovine serum. Flow cytometric analysis and imm unocytochemical staining demonstrated that c-Mpl was expressed on DC. Furth ermore, the expression of c-Mpl mRNA was detected in DC by RNase protection assay. However, when TPO was added to the culture system there were no sig nificant changes in the differentiation and mixed leucocyte-stimulating cap acity of DC. These findings suggest that TPO may be administered following cord blood transplantation without significant augmentation of antigen pres entation mediated by DC.