miR-155 promotes FLT3-ITD–mediated myeloid expansion in the spleen and blood. (A) Breeding strategy to create FLT3-ITD 155^−/− mice. (B) PCR confirming the presence of FLT3-ITD and loss of miR-155. (C) Representative spleens for the different mouse groups. (D) Spleen size quantified by both weight and overall cellularity. (E) Hematoxylin and eosin staining of spleens from different mouse groups. Representative images are shown. White arrows denote areas of myeloproliferation. Full-sized images, original magnification ×100; inset, original magnification ×1000. Scale bar, 100 µm. (F) Total numbers of CD11b⁺ Gr1⁺ cells, CD11b⁺ Gr1^– cells, B220⁺ cells, and Ter119⁺ cells in the spleen determined by flow cytometry. (G) Complete blood counts for various blood cells in different mouse groups. Data are representative of at least 3 independent experiments. Each point represents a sample from 1 mouse. Data represented as mean ± SEM. *P ≤ .05; **P ≤ .01; ***P ≤ .001; ****P ≤ .0001; ns, P > .05. KO, knockout.