Injection of influenza virus into NOD/SCID mice reconstituted with human DCs triggers activation and migration of CD11c⁺ mDCs. (A-B) Bone marrows of mice no. 9, no. 6, and no. 13 in Figure 5 were depleted of murine cells as described in “Material and methods,” and their cell surface phenotype was analyzed by flow cytometry. Surface expression of the DC activation/maturation markers CD54 (ICAM-1), costimulatory molecules such as CD86, CD80, and CD40, as well as CD83 were determined (boxes indicate frequency of CD11c⁺ cells expressing indicated marker in the total fraction of human cells enriched from the bone marrow, < 1% of expression in mice that did not receive virus). (C-D) Spleen section of mice engrafted with human cells that received either vehicle control (C, left panels) or flu virus (D, right panels). Red illustrates structure of the tissue by nuclei labeling with 7AAD. Human cells are labeled with anti–human HLA-DR-FITC. Spleens of mice infected with influenza virus display aggregation and infiltration of human cells (areas are representative of the whole section). (E-F) Human cellular aggregates in the spleen of NOD/SCID mice infected with virus are composed predominantly of HLA-DR⁺CD11c⁺ mDCs, and only rare double staining of CD11c⁺ with IgD can be seen. (E) Double staining with anti-human HLA-DR-FITC (green), anti–human CD11c-PE (red), and overlay at × 63 magnification (no. 13 from Figure 6). (F) Triple staining with anti–human IgD-FITC (green), anti–human CD11c-PE (red), anti–human HLA-DR-Cy5 (blue), and overlay at × 63 magnification (no. 6 from Figure 6). Note comparatively high levels of expression on DCs (purple) as opposed to IgD⁺ B cells and strong staining with IgD. Original magnification, × 40.