Expression of CD41 and c-mpl does not indicate commitment to the megakaryocyte lineage during haemopoietic development

Haemopoietic progenitors with the phenotype expected of early megakaryocyte precursors (CD34(+)CD41(+)) were isolated from normal human bone marrow or induced in culture from CD34(+)CD41(-) bone marrow cells by treatment with thrombopoietin (TPO) or IL-3, We found that although this population inclu ded the majority of cells that can form CFU-MK in culture, it also containe d both erythroid and myeloid progenitors. The clonogenic potential of the C D34(+)CD41(+)-induced cells was greater than that of isolated CD34(+)CD41() cells in that the isolated cells only formed CFU-MK and BFU-e, whereas th e induced cells formed myeloid colonies as well. Glycophorin was found on i solated CD34(+)CD41(+) cells, not on induced cells. Its presence distinguis hed between MK and erythroid progenitors. Separation of a CD34(+)CD41(+) gl ycophorin A(+) population resulted in the isolation of a highly purified po pulation of BFU-e. A major portion of the cells that expressed CD34(+)CD41( +), in either cohort, were of the erythroid lineage. True MK progenitors we re present in the CD34(+) population in greater proportion than in whole ma rrow and were further enriched amongst CD34(+) populations that expressed C D41. The presence of the thrombopoietin (TPO) receptor, c-mpl, did not corr elate with inducibility of the gpIIbIIIa complex since essentially all CD34 (+) progenitors, including the earliest identifiable human haemopoietic pro genitors (CD34(+)CD38(-) cells), expressed c-mpl mRNA detectable by PCR reg ardless of their ultimate fate, Thus neither the expression of CD41 nor the expression of c-mpl was predictive of commitment to the MK lineage.