Mast cells and basophils are distinct immune cells. Mast cells line the tissues exposed to the environment. In comparison, basophils circulate in the blood. Mast cells and basophils arise from a common stem cell precursor in the bone marrow. But basophils are more related to macrophages than mast cells. Mast cells enter the blood as immature cells that mature in the tissues. In comparison, basophils enter the blood as mature cells. So, basophils do not mature into mast cells.