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 he re, a cell population in murine fetal blood that fulfills the criteria of progenitor mastocytes was identified. It is defined by the phenoty pe Thy-1(lo)c-Kit(hi), contains cytoplasmic granules, and expresses RN As encoding mast cell-associated proteases but lacks expression of the high-affinity immunoglobulin E receptor. Thy-1(lo)c-Kit(hi) cells gen erated functionally competent mast cells at high frequencies in vitro but lacked developmental potential for other hematopoietic lineages. W hen transferred intraperitoneally, this population reconstituted the p eritoneal mast cell compartment of genetically mast cell-deficient W/W -v mice to wild-type levels.