Expression of the c-kit gene product in normal and neoplastic mast cells but not in neoplastic basophil/mast cell precursors from chronic myelogenous leukaemia.

The expression of the c-kit gene product has been examined in normal mast cells, mast cell neoplasms, and basophil/mast cell precursors obtained from patients with chronic myelogenous leukaemia (CML). Formalin-fixed, paraffin-embedded sections or smears fixed with formalin vapour were studied by immunohistochemical methods, using a polyclonal antibody against the c-kit gene product. Normal and neoplastic mast cells showed a positive immunoreaction for c-kit gene product, but neoplastic basophil/mast cell precursors from CML patients lacked c-kit gene product by immunohistochemical and flow cytometric methods, even in cells having mast cell granules, together with or without basophil granules. Mast cell tryptase was, however, expressed in normal and neoplastic mast cells and basophil/mast cell precursors containing mast cell granules. In addition, cells of monocyte/macrophage lineage lacked c-kit gene product. These findings indicate that the c-kit gene product may play an important role in the development and function of mast cell but not of cell of basophil and monocyte/macrophage lineage.