Immunohistochemical properties of bone marrow mast cells in systemic mastocytosis: Evidence for expression of CD2, CD117/Kit, and bcl-x(L)

In an attempt to identify novel diagnostic markers for mast fell (MC)-proli ferative disorders, serial bone marrow (bm) sections of 22 patients with ma stocytosis (systemic indolent mastocytosis, n = 19; mast cell leukemia [MCL ], n = 1; isolated bm mastocytosis, n = 2) were analyzed by immunohistochem istry using antibodies against CD2, CD15, CD29, CD30, CD31, CD34, CD45, CD5 1, CD56, CD68R, CD117, HLA-DR, bcl-2, bcl-x(L), myeloperoxidase (MPO), and tryptase. Staining results revealed expression of bd-x,, CD68R, and tryptas e in neoplastic MCs (focal dense infiltrates) in all patients. Mastocytosis infiltrates were also immunoreactive for CD45, CD117 (Kit), and HLA-DR In most cases, the CD2 antibody produced reactivity with bm MCs in mastocytosi s, whereas in control cases (reactive bm, immunocytoma, myelodysplastic syn drome), MCs were consistently CD2 negative. Expression of bcl-2 was detecta ble in a subset of MCs in the patient with MCL, whereas no reactivity was s een in patients with SIM or bm mastocytosis. Mastocytosis infiltrates did n ot react with antibodies against CD15, CD30, CD31, CD34, or MPO. In summary , our data confirm the diagnostic value of staining for tryptase, Kit, and CD68R in mastocytosis. Apart from these, CD2 may be a novel useful marker b ecause MCs in mastocytosis frequently express this antigen, whereas MCs in other pathologic conditions are CD2 negative. Copyright (C) 2001 by W.B. Sa unders Company.