Immunocytochemistry of normal bone marrow.

(A) shows normal bone marrow stained with anti–Notch-1 antibody. Positive staining is brown-black and the counterstain is a light-blue hematoxylin. Positive staining is seen in the cytoplasm and appears to be on the cell membrane in both erythroid precursors (seen in a patch on the left as a narrow cytoplasmic rim in round cells with round nuclei) and in myeloid precursors (seen in a patch on the right as cytoplasmic staining of polygonal cells). Background staining with an isotype-matched antibody of irrelevant specificity was minimal (B). (C) shows a double stain for Notch-1 and glycophorin, with the latter seen as red. A portion of the glycophorin-staining cells also contained Notch-1. This portion contained mainly the larger more immature glycophorin-staining cells, which the more mature, smaller erythroid precursors did not stain for Notch 1. A few cells in this field contain both. It appears that Notch-1 is lost as the cells mature and gain glycophorin. (D) shows double-staining for Notch-1 and myeloperoxidase, with the myeloperoxidase staining red. The majority of cells in this field are of the granulocytic lineage, staining with myeloperoxidase and sometimes showing polylobulated nuclei characteristic of mature neutrophils. The Notch-1 stained cells appear not to be myeloperoxidase positive, even when lightly stained. Some of the Notch-1 stained cells are clearly small, round erythroid precursors, others have a more polygonal cytoplasmic shape and sometimes a clefted nucleus consistent with a monocytic cell. All photomicrographs were taken at magnification × 60.