Concentration of mast‐cell progenitors in bone marrow, spleen, and blood of mice determined by limiting dilution analysis

When hematopoietic cells of congenic +/+ mice were injected into the skin of genetically mast-cell-depleted (WB X C57BL/6)F1-W/Wv mice, mast cells appeared at the injection site. The donor origin of developing mast cells was confirmed by using giant granules of C57BL/6-bgl/bgl mice as a marker. When the number of injected cells was decreased, the proportion of injection sites at which mast cells did not appear increased according to the expected frequency of null response in a Poisson distribution. Therefore, such proportions were used to calculate the concentration of mast-cell precursors in the bone marrow, spleen, and peripheral blood. The relative concentration of mast-cell precursors in these tissues was similar to that of spleen-colony-forming cells. The present method seems useful as a semiquantitative in vivo assay for a population of progenitor cells which are committed to differentiate into mast cells.