The role of miRNAs in mast cells and other innate immune cells.

MicroRNAs (miRNAs) are a large class of small regulatory molecules able to control translation of target mRNAs and consequently to regulate various biological processes at a posttranscriptional level. Their importance is highlighted by the fact that altered miRNA expression is linked to a variety of human diseases, particularly cancer. Accordingly, miRNA biogenesis itself must be carefully regulated, both transcriptionally and posttranscriptionally. Here, we focus on the role of miRNAs in three lineages of myeloid cells important in both innate and acquired immunity: mast cells, macrophages, and dendritic cells. These three cell types are strategically located throughout the body tissues, where they can respond to foreign material, danger, and inflammatory signals. We discuss the role of miRNAs in these cell types, with a special focus on three of the most extensively studied miRNAs, namely miR-221, miR-146a, and miR-155. We also discuss the role of cell-to-cell transfer of miRNAs in dendritic cells, mast cells, and macrophages, and we speculate about possible future directions in the field.