...to these alterations in CTMCs, MMC numbers were comparable between Mcpt5Cre/Dicerfl/fl mice and Dicerfl/fl control animals, as indicated by unchanged serum levels of mMCP-1 (Fig 1, H) and comparable expression of Mcpt1 and Mcpt2 mRNA in the small intestine in both groups (Fig 1, I and J). Because MCs are major effector cells of anaphylaxis, we next sought to investigate the response of Mcpt5Cre/Dicerfl/fl mice in IgE-mediated passive systemic anaphylaxis (Fig 1, K). In line with our findings, Dicer ablation in vivo has been shown to also affect maturation of granulocyte/macrophage progenitors toward neutrophils, macrophages, and dendritic cells, as well as T-cell differentiation, B-cell development, and germinal center formation.2,8 Expression of Mcpt5Cre has previously been demonstrated to be highly specific for CTMCs,4 with the exception of TH2 cell-mediated expansion of MMCs.9 To further assess the specificity of Mcpt5Cre-mediated deletion of Dicer, we next analyzed the number of different myeloid and lymphoid cells in peripheral blood, the spleen, and the peritoneal cavity (Fig 2).