Identification and characterization of human hemopoietic mast cell colonies

Persisting mast cell colonies from human bone marrow and cord blood cells grown in semisolid agar cultures for over 56 days have been positively identified and characterized using morphology and cytochemistry. Mast cells demonstrated the following features: Cytoplasmic granules frequently contained the specific and characteristic papyrus rolls (transmission electron microscopy); mature cells were positive to the mouse monoclonal antibody YB5.B8 specific for human mast cells (raised against acute myeloid leukemia cells) and RPA-M1 specific for human monocytes but negative to the human basophil monoclonal antibody Bsp-1; morphologically the cells were large (diameter 20-25 micron), deeply basophilic, and contained granules that measured up to 2 micron in diameter (May-Grünwald-Giemsa stain); the presence of heparin by the thrombin clotting time and positive staining with toluidine blue and alcian blue; the presence of histamine by a positive fluorescent o-phthalaldehyde stain; the presence of IgE receptor sites with human IgE and a rabbit anti-human IgE second antibody; and a unique zone of lysis around mast cell colonies occurred when cultured on peripheral blood feeder layers in agar plates that was not present around monocytic, neutrophilic, or eosinophilic colonies under the same culture conditions. Our results identify the cells in persisting colonies as mast cells and describe some specific characteristics that distinguish these cells from basophils.