Mutant Mice as a Tool for Investigation of Mast Cell Differentiation^*

抄録

Mutant mice are an invaluable tool for investigation of mast cell differentiation. Giant granules of bg^J/bg^J mice are used as a marker to identify the origin of mast cells. Mice of W/W^V, SI/SI^d and mi/mi genotypes lack mast cells, and are useful not only for studying the differentiation processes but also clarifying the regulation mechanisms. Although mast cells had been considered to be derived from undifferentiated mesenchymal cells, we showed that mast cells are a unique class of blood cells. Unlike most blood cells, undifferentiated precursors of mast cells migrate in the bloodstream, invade tissues, proliferate there and then differentiate. Even after differentiation, some mast cells may proliferate. Moreover, after functioning (i.e., degranulation), some mast cells may proliferate and produce granules again. Differentiation of mast cells is promoted by both T cells and fibroblasts and is suppressed by differentiated mast cells. Mast cell deficiency of W/W^v, Sl/Sl ^d and mi/mi mice is attributed to defects of fibroblast-dependent mechanisms, and deficient mast-cell reaction in nude athymic mice to depletion of T cells.