HUMAN BONE-MARROW MAST-CELLS FROM INDOLENT SYSTEMIC MAST-CELL DISEASECONSTITUTIVELY EXPRESS INCREASED AMOUNTS OF THE CD63 PROTEIN ON THEIRSURFACE

The quantitative measurement of the expression of both cytoplasmic and surface CD63 antigen by human mast cells from both normal and patholo gical bone marrow samples was studied by use of flow cytometry. Our ma jor goal was to analyze whether in vivo CD63 expression by human hone marrow mast cells could be useful to discriminate bone marrow mast cel ls from patients with mastocytosis from other conditions. For that pur pose, a total of 65 subjects corresponding to 12 healthy volunteers, 2 5 B-cell chronic lymphoproliferative disorders, 5 reactive bone marrow samples, 4 myelodysplastic syndromes, and 19 mastocytosis were analyz ed. The expression of both surface and cytoplasmic CD63 by human bone marrow mast cells is clearly demonstrated. Our results show that high amounts of CD63 are present in human bone marrow mast cells most of it corresponding to an intracellular localization. No significant differ ences in CD63 expression were observed as regards both total and cytop lasmic CD63, except for higher CD63 levels in adult patients with mast ocytosis (P = 0.05). By contrast, the mean level of surface CD63 signi ficantly varied between the different groups of individuals. According ly, patients with monoclonal gammopathies displayed a slight decrease (P = 0.1) in surface CD63 expression, whereas bone marrow mast cells f rom adults with indolent systemic mast cell disease showed significant ly (P = 0.0005) higher levels of surface CD63 as compared to healthy c ontrols. (C) 1998 Wiley-Liss, Inc.