Phenotypic and functional defects exhibited by miR155^−/− DCs. (A) Unstimulated and LPS-treated BM-DCs prepared from WT and miR155^−/− mice were stained with antibodies against CD11c, and the frequencies of cells exhibiting a characteristic dendritic morphology were determined. Representative images are shown at the left; dendritic protrusions are indicated with arrows. The bar graph represents the means and SDs derived from 3 independent BM-DC preparations; ns, not significant; **P < .01. The numbers of cells examined are indicated for each bar. (B) Cell-surface CD86, CD40, CD80, and I-A^b expression was analyzed by flow cytometry for unstimulated and LPS-treated BM-DCs from WT and miR155^−/− mice. Histograms are representative of 3 experiments. (C) The mean fluorescence intensity (MFI) for cell-surface CD86 and CD40 expression was determined by flow cytometry for unstimulated and LPS-treated BM-DCs from WT and miR155^−/− mice. The means and SDs derived from 3 independent experiments are shown; *P < .05; **P < .01. (D) LPS-treated BM-DCs from WT and miR155^−/− mice were loaded with OVA peptide (left panels) or OVA protein (right panels) and cocultured with OVA-specific CD4⁺ T cells purified from TCR-transgenic OTII mice. BM-DCs that had not been loaded with antigen (−OVA) were used as negative controls. T-cell activation was determined by the analysis of cell-surface CD69 expression (top panels, relative frequencies of CD69⁺ cells) or secretion of IL2 into the supernatants (bottom panels, relative IL2 secretion). The means and SDs derived from 3 independent experiments are shown; *P < .05; **P < .01.