Immunohistochemical and immunocytochemical detection of HDC in CML cells. (A-B) Immunohistochemical analysis of bone marrow (BM) cells for expression of histidine decarboxylase (HDC) in a patient with accelerated-phase CML. Adjacent BM sections were stained with the basophil-specific antibody 2D7 (A) and an antibody against HDC (B). Original magnification, ×100. (C-D) Immunocytochemistry of primary CML cells obtained from the same patient. Slides were stained with the basophil-specific antibody 2D7 (C) and an antibody against HDC (D). Original magnification, ×40. (E-G) Measurement of histamine in cell-free supernatants of leukemic cells obtained from patients with chronic-phase CML (n = 4) (E), from patients with accelerated-phase CML (n = 3) (F), and in normal BMMCs (n = 3) (G). Isolated CML cells were cultured in RPMI 1640 medium and 10% FCS for various time periods as indicated. Concentrations of histamine in cell-free supernatants were determined by radioimmunoassay (RIA). Results represent the mean ± SD of 3 or 4 independent experiments.