Pathologic analysis of tissues from Mx1-Cre, Nf1 ^flox/flox mice. (A) Cre⁺ mice demonstrate progressive splenomegaly. Data are presented as the mean ± SEM. (A,C) Asterisks indicate significant differences (P < .05) between the Cre⁺ and Cre^- animals. (B) Spleen (top) sections from Cre⁺ mice demonstrate expansion of the red pulp with myeloid infiltration. Liver sections (bottom) show periportal infiltration. (C) Manual differential counts of the percentage of nonerythroid cells in blood, bone marrow (BM), and spleen from Cre⁺ and Cre^- mice. Note that the bone marrow myeloid cells show a normal pattern of differentiation and that the spleen shows a massive increase in myelopoiesis. The data are shown as the mean ± SD. (D) Cytospins of bone marrow and spleen in a Cre⁺ mouse with MPD show maturing neutrophilic and monocytic elements (original magnification × 200). (E) Representative FACS data from Cre^- (left) and Cre⁺ (right) bone marrows. Cre⁺ mice with MPD demonstrate an increased percentage of Gr1⁺/Mac1⁺ cells (51% versus 22%). There is marked expansion in the Mac-1⁺/Gr-1^lo subset (11.5% in Cre⁺ versus 2.13% in Cre^- mice), which is consistent with an increase in monocytic cells. The numbers shown indicate the percentage of cells within each quadrant.