Loss of miR-142 affects the composition of the myeloid compartment in vivo. (A) Quantitative real-time PCR of splenic CD4⁺ and CD8α⁺ DCs isolated from miR-142^+/+, miR-142^+/−, and miR-142^−/− mice. The detection of miR-142-3p and miR-142-5p was normalized to endogenous U6 levels. All expression levels were calculated to the miR-142-3p level in miR-142^+/+ CD4⁺ DCs. Note the reduced expression of miR-142-3p in WT CD8α⁺ DCs compared with CD4⁺ DCs. (B) β-Galactosidase activity in ex vivo myeloid cell populations isolated from miR-142^+/+ (black filled), heterozygous mutant miR-142 LacZ knock-in mouse (gray filled), or homozygous mutant miR-142 LacZ knock-in mouse (white filled) as determined by the FACS-FDG assay. (C) Quantification of mononuclear phagocyte populations in the BM of miR-142–deficient mice and control animals. Only MPs (0.044% ± 0.009% and 0.031% ± 0.005% of total BM cells in WT and miR-142^−/− mice, respectively) and pDCs (1.2% ± 0.18% and 0.6% ± 0.05% of total BM cells in WT and miR-142^−/− mice, respectively) showed significant reduced cell numbers in miR-142^−/− mice. (D) Splenomegaly in 6-week-old miR-142^−/− mice (65.2 ± 8.5 vs 168 ± 30.2 mg in WT and miR-142^−/− mice, respectively). Thymi showed no obvious weight changes (68.5 ± 8.5 vs 63.3 ± 11.2 mg in WT and miR-142^−/− mice, respectively). (E) Flow cytometric analysis of primary (thymi) and secondary lymphoid organs (skin draining lymph nodes, mesenteric lymph nodes, and spleens) for the infiltration of myeloid cells in miR-142^−/− and miR-142^+/+ mice. Neutrophils were identified as CD115⁻CD11b Gr1⁺; Ly6C⁺ monocytes as CD115⁺CD11b⁺Gr1⁺; and Ly6C⁻ monocytes as CD115⁺CD11b⁺Gr1⁻. Three animals in an age of 6 weeks were used in each group. *P < .05 was considered significant using a Student 2-tailed t test.