[Regulatory mechanisms of mast cell differentiation]

Mast cells are a progeny of the multipotential hematopoietic stem cell. Most of progenies of the stem cell complete their differentiation within the bone marrow, but precursors of mast cells leave the bone marrow, migrate in blood, and invade into tissues. After the invasion, precursors proliferate and differentiate into mast cells. An appreciable proportion of mast cells retain proliferative potential after differentiation, and even after degranulation, some mast cells can proliferate and recover the original morphology. Proliferation of mast cells are regulated by both T cell-derived factors (i.e., IL-3 and IL-4) and fibroblast-derived factor(s). Mice of either W/Wv or Sl/Sld genotype lack mast cells, but mast cells do develop when bone marrow cells of W/Wv or Sl/Sld mice were cultured in the presence of T cell-derived factors. Mast cells derived from W/Wv mice cannot respond fibroblast-derived factor(s) and fibroblasts derived from Sl/Sld mice cannot support mast cells of normal mouse origin. Phenotypes of mast cells are determined by the environment in which the mast cells differentiated. However, when mast cells are transplanted into a new environment which is different from the original one, the mast cells acquire the phenotype which are dependent on the second environment.