Two novel mast cell phenotypic markers, monoclonal antibodies Ki-MC1 and Ki-M1P, identify distinct mast cell subtypes

Summary In order to identify more specific or selective mast cell markers, the reactivity of two monoclonal antibodies, Ki-MC1 and Ki-M1P, was studied by immunohistochemistry in two human cell lines (mast cell line HMC-1, basophilic cell line KU812), in mast cells cultured from blood precursors, in adherent mononuclear cells from peripheral blood, and in mast cells of tissue sections from 1 3 urticaria pigmentosa lesions, live mastocytomas and live normal skin specimens. Toluidine blue staining, fluorescence staining with FITC-conjugated avidin, and immunohistochemical staining (APAAP) with other mast cell reactive monoclonal antibodies, was performed for comparison. Double staining with the APAAP method, using the Ki-antibodies and toluidine blue, was also carried out. Both Ki-antibodies showed reactivity for skin mast cells, but with a different staining pattern. In addition, the Ki-MC1 antibody did not react with the cell lines, and reacted only with a few peripheral blood mononuclear cells and cultured mast cells. In contrast, the Ki-M1P antibody reacted with almost all cultured mast cells and blood mononuclear cells, but stained only about one-half of lesional and one-fifth of normal skin mast cells. Ki-M1P also reacted with many toluidine blue-negative dermal cells, particularly in urticaria pigmentosa. Ki-MC1 antibody can thus be considered as a useful additional marker for normal skin mast cells. In contrast, the Ki-M1 P antibody primarily identifies immature mast cells and monocytes/macrophages, suggesting that these cell types probably originate from the same bone marrow precursor.