Figure 1
Immunohistochemical expression of BDCA-2 in normal lymphoid tissues and hematopoietic neoplasms. BDCA-2 immunostaining of a reactive lymph node (A) identifies aggregates and dispersed PDCs; in contrast, note that anti-CD123 applied on a serial section labels not only PDCs but also histiocytes and high endothelial venule endothelium (B). BDCA-2 is selectively expressed on PDCs and not on T-cells, B-cells, and macrophages/myeloid dendritic cells, as shown by double immunostainings, respectively, for BDCA-2 and CD3 (C), PAX-5 (D), and CD11c (E). In the thymus, BDCA-2 highlights scattered PDCs located in the medulla (F), where they frequently surround Hassall’s corpuscles (insert). In the spleen, BDCA-2-positive PDCs are particularly located at the periphery of the white pulp (G). Neoplastic PDCs show strong positivity for BDCA-2, as illustrated in representative cases of BPDCN with cutaneous (H) and bone marrow involvement (I-J). BDCA-2 can be very helpful in detecting minimal tumor cell infiltrate in the bone marrow (J).It must be noted, however, that BDCA-2 reactivity in this tissue can be variable, likely due to antigen degradation consequently from decalcification. BDCA-2 is totally negative on tumor cells in 2 representative samples of AML (K) and ALL (L), in which rare reactive PDCs are also detected. In the AML case (M2 in FAB classification) myeloid blasts are highlighted by anti-CD34. Single immunostaining for BDCA-2 was performed after heat-based antigen retrival in ethylenediaminetetraacetic acid buffer, pH 8.0; reactivity was revealed using the NovoLink Polymer kit (Leica Microsystems, Newcastle upon Tyne, United Kingdom) followed by diaminobenzidine as brown chromogen. For double immunostainings (C-E and K), the blue reaction visualizing the second antibody was obtained using the Mach 4-AP kit followed by Ferangi Blue as chromogen (Biocare Medical, Concord, CA). Images were obtained with the BX60 microscope, DP-70 digital camera, and image processing software (Olympus, Hamburg, Germany). Original magnifications, ×40 (F), ×100 (G-I), ×200 (A, B, K), and ×400 (C-E, inset in F, and J and L).

Immunohistochemical expression of BDCA-2 in normal lymphoid tissues and hematopoietic neoplasms. BDCA-2 immunostaining of a reactive lymph node (A) identifies aggregates and dispersed PDCs; in contrast, note that anti-CD123 applied on a serial section labels not only PDCs but also histiocytes and high endothelial venule endothelium (B). BDCA-2 is selectively expressed on PDCs and not on T-cells, B-cells, and macrophages/myeloid dendritic cells, as shown by double immunostainings, respectively, for BDCA-2 and CD3 (C), PAX-5 (D), and CD11c (E). In the thymus, BDCA-2 highlights scattered PDCs located in the medulla (F), where they frequently surround Hassall’s corpuscles (insert). In the spleen, BDCA-2-positive PDCs are particularly located at the periphery of the white pulp (G). Neoplastic PDCs show strong positivity for BDCA-2, as illustrated in representative cases of BPDCN with cutaneous (H) and bone marrow involvement (I-J). BDCA-2 can be very helpful in detecting minimal tumor cell infiltrate in the bone marrow (J).It must be noted, however, that BDCA-2 reactivity in this tissue can be variable, likely due to antigen degradation consequently from decalcification. BDCA-2 is totally negative on tumor cells in 2 representative samples of AML (K) and ALL (L), in which rare reactive PDCs are also detected. In the AML case (M2 in FAB classification) myeloid blasts are highlighted by anti-CD34. Single immunostaining for BDCA-2 was performed after heat-based antigen retrival in ethylenediaminetetraacetic acid buffer, pH 8.0; reactivity was revealed using the NovoLink Polymer kit (Leica Microsystems, Newcastle upon Tyne, United Kingdom) followed by diaminobenzidine as brown chromogen. For double immunostainings (C-E and K), the blue reaction visualizing the second antibody was obtained using the Mach 4-AP kit followed by Ferangi Blue as chromogen (Biocare Medical, Concord, CA). Images were obtained with the BX60 microscope, DP-70 digital camera, and image processing software (Olympus, Hamburg, Germany). Original magnifications, ×40 (F), ×100 (G-I), ×200 (A, B, K), and ×400 (C-E, inset in F, and J and L).

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