Ultrastructural evidence for the common origin of human mast cells and basophils

Although the functional similarity of basophils and mast cells is widely accepted, their distinctive morphological features have been taken to indicate the existence of two different, albeit functionally complementary, cell systems. The recent demonstration that mast cells as well as basophils originate from the bone marrow raises the possibility that these cells derive from the same precursor. This report provides evidence for this theory by describing a distinctive “intermediate” cell possessing the ultrastructural features typical of both basophils and mast cells. These cells were encountered in three patients with myeloproliferative diseases and may thus be more readily found in states of disturbed myelopoiesis. These observations have given impetus for the first comparative description of the ultrastructure of human basophils, human mast cells, and the newly recognized intermediate cell within a single report.