Mast-cell precursors in various haematopoietic colonies of mice produced in vivo and in vitro

S ummary . We have examined mast-cell precursors in various in vivo and in vitro haematopoietic colonies of mice. Cells from haematopoietic colonies of (WB x C57BL/6)F₁- +/+ mouse origin were injected into the skin of the congeneic W/W^v mice which are genetically depleted of tissue mast cells. The appearance of mast-cell clusters at the injection site indicated the presence of mast-cell precursors in the injected cell suspension. More than 40% of 12 d exogenous spleen colonies and 14 d in vitro mixed colonies contained mast-cell precursors, but only a small proportion of 7 d exogenous spleen colonies, 9 d in vitro erythroid bursts or 14 d large in vitro neutrophil-macrophage colonies contained mast-cell precursors. Neither transient endogenous erythroid spleen colonies examined at the fifth day nor 7 d in vitro neutrophil-macrophage colonies contained mast-cell precursors. Among 12 d spleen colonies mast-cell precursors were more frequent in the predominantly neutrophil than the predominantly erythroid colonies but 14 d in vitro mixed colonies, in which erythroid cells were predominant, contained mast-cell precursors more frequently than 14 d in vitro neutrophil-macrophage colonies. Therefore, differentiation of mast cells seems to be independent of either the neutrophil-macrophage or erythroid cell lineages.