Human myeloid precursor cells do not possess or produce procoagulant activity (PCA)

The procoagulant cellular activity (PCA) of human myeloid precursor cells was evaluated after fractionation of normal bone marrow cells over a discontinuous albumin density gradient. No PCA was documented in any of the six freshly isolated fractions (F1-F6); significant amounts of PCA were instead produced, after a 4-h endotoxin preincubation, in fractions F1 and F2, which, unlike the other fractions, contained up to 5% monocyte-macrophages. After removal of the latter by plastic adherence, PCA was abolished. This study shows that PCA can be produced only by monocyte-macrophages upon endotoxin activation, while myeloid precursor cells, at all stages of differentiation, are incapable of PCA. The PCA demonstrated in some human acute myeloid leukemias, other than that of the monoblastic subgroup, appears therefore to be related to the neoplastic transformation rather than to a maturation arrest or to a toxemic stimulation.