Phenotypic Characterization of the Human Mast‐Cell Line HMC‐1

The cell line HMC‐1, derived from a patient with mast cell leukaemia, is the only established cell line exhibiting a phenotype similar to that of human mast cells. This paper reports on a detailed characterization of the expression of a panel of markers for various types of immature and mature haematopoietic cells in the HMC‐1. We also studied the potential of HMC‐1 to differentiate upon treatment with conditioned media from the human T‐cell line Mo, retinoic acid or DMSO. HMC‐1 was found to express several mast cell‐related markers. A high expression of Kit, the receptor for stem‐cell factor, was detected. The majority of the cells were stained with a MoAb against the mast cell‐specific serine protease tryptase. Of particular interest was the finding that β‐tryptase mRNA, but not a‐tryptase mRNA, was expressed in HMC‐1. Using enzyme‐histochemistry we were able to show that the β‐tryptase was enzymatically active, indicating that tryptase can form active homotetramers. Both heparin and chondroitin sulfate were found to be present in approximately equal amounts. HMC‐1 lacked surface expression of the high‐affinity IgE receptor, which was confirmed by the absence of mRNA of the α‐ and β‐chains of the IgE‐receptor complex. However, a strong expression of the 7‐chain of the IgE‐receptor complex was detected. A positive staining of the monocyte/macrophage marker CD68 was obtained, as well as a strong hybridization signal for the eosinophilic/basophilic‐related differentiation marker the Charcot‐Leyden crystal. Treatment of HMC‐1 with conditioned media from the human T‐cell line Mo, retinoic acid or DMSO induced only moderate changes in the surface or intracellular expression of the studied markers. The agents tested neither induced any of the monocyte/ granulocyte markers examined, nor expression of the FceRIα‐chain.