Identification of a Committed Precursor for the Mast Cell Lineage

Mast cells originate from hematopoietic stem cells, but the mast cell-committed precursor has not been identified. In the study presented here, a cell population in murine fetal blood that fulfills the criteria of progenitor mastocytes was identified. It is defined by the phenotype Thy-1 lo c-Kit hi , contains cytoplasmic granules, and expresses RNAs encoding mast cell-associated proteases but lacks expression of the high-affinity immunoglobulin E receptor. Thy-1 lo c-Kit hi cells generated functionally competent mast cells at high frequencies in vitro but lacked developmental potential for other hematopoietic lineages. When transferred intraperitoneally, this population reconstituted the peritoneal mast cell compartment of genetically mast cell-deficient W / W v mice to wild-type levels.