hMRP8-NPMc⁺ transgenic mice develop a nonreactive myeloproliferation with expansion of mature granulocytes/monocytes. (A) Table showing the total number of mice analyzed from different transgenic lines, their age range, and myeloproliferation (MP) penetrance involving either BM or spleen. (B) Composite data from age-matched littermates of indicated genotypes demonstrating splenomegaly in NPMc⁺ transgenic mice (mean ± SEM; NT, n = 5; NPMc⁺ 28, n = 5). **P < .01. Spleen masses are 160 ± 60.8 mg for NT (n = 5) versus 567 ± 284 mg for NPMc⁺ 28 (n = 5; P = .014). (C) Histopathologic sections of BM and spleen from representative NT and NPMc⁺ transgenic mice. (i) NT BM (hematoxylin and eosin, original magnification, ×1000). (ii) NT BM cytospin (original magnification, ×1000). represents an erythroblast; , granulocytes. (iii) NPMc⁺ BM (hematoxylin and eosin, original magnification, ×1000). (iv) NPMc⁺ BM cytospin (original magnification, ×1000). represent granulocytes. (v) NT spleen (hematoxylin and eosin, original magnification, ×40). (vi) NT spleen (hematoxylin and eosin, original magnification, ×400). (vii) NPMc⁺ spleen (hematoxylin and eosin, original magnification, ×40). represents areas of expanded red pulp with extramedullary hematopoiesis. (viii) NPMc⁺ spleen (hematoxylin and eosin, original magnification, ×400). represents extramedullary hematopoiesis. (D) Flow cytometric analysis of single-cell suspensions of BM and spleen from representative NT and NPMc⁺ transgenic mice demonstrates an increase in granulocytic/monocytic (Mac-1⁺;Gr-1⁺) and mature myeloid (Mac-1⁺;cKit⁻) cells with a corresponding decrease in the amount of B (B220⁺) and T (CD3⁺) lymphoid cell populations. (E) Quantification of granulocytic/monocytic (Mac-1⁺;Gr-1⁺), mature myeloid (Mac-1⁺/cKit⁺), B cells (B2200⁺), and T cells (CD3⁺) in BM and spleen of age-matched NT and NPMc⁺ transgenic mice analyzed as in panel D (mean ± SEM; NT, n = 6; NPMc⁺ 28, n = 6). *P < .05. **P < .01. ***P < .001. n.s. indicates not statistically significant.