Development of mast cells and basophils: processes and regulation mechanisms.

Mast cells and basophils are offspring of the multipotential hematopoietic stem cell. Although mast cells sometimes are misunderstood as basophils that have invaded connective or mucosal tissue, these two kinds of basophilic cells are distinguishable by morphology and surface antigenicity. Developmental processes of mast cells and basophils are different. Basophils complete their differentiation within the bone marrow, but precursors of mast cells leave the bone marrow, invade connective or mucosal tissue, proliferate, and differentiate into mast cells. The mechanisms regulating development are different between mast cells and basophils. Both T cell-dependent and fibroblast-dependent mechanisms are involved in the development of rodent mast cells, but only the fibroblast-dependent mechanism is known for development of human mast cells and only the T cell-dependent mechanism for the development of basophils of both rodents and humans. The most important cytokine for the T cell-dependent mechanism appears to be interleukin-3, whereas for the fibroblast-dependent mechanism it appears to be the ligand for the c-kit receptor (ie, stem cell factor).