Increased myelomonocytic cell population in enlarged spleens of p15Ink4b^fl/fl-LysMcre mice. (A) Composite spleen weights from age-matched mice of indicated genotypes demonstrate splenomegaly in p15Ink4b^fl/fl-LysMcre mice. Data are mean ± SD. P value was calculated using the Student t test and shown (p15Ink4b^wt/wt-LysMcre n = 10; p15Ink4b^fl/fl-LysMcre, n = 10). (B) Hematoxylin and eosin and immunohistochemistry staining of paraffin-embedded spleen sections from wild-type (wt/wt) and floxed (fl/fl) mice. Scale bars represent 20 μm. (C) Gr-1 and Mac-1 FACS analysis of representative single-cell spleen suspensions confirmed expansion of mature myeloid (Gr-1⁺/Mac-1⁺) and monocytic (Gr-1^−/lo/Mac-1⁺) cell populations. (D) The frequency of B220 and F4/80⁺ cells in the spleen of p15Ink4b^wt/wt- (n = 4) and p15Ink4b^fl/fl-LysMcre (n = 4) mice presented as a percentage of the total nucleated cells.