Extracellular RNAs: A secret arm of immune system regulation

The immune system has evolved to protect multicellular organisms from the attack of a variety of pathogens. To exert this function efficiently, thesystemhas developed the capacity to coordinate the function of different cell types and the ability to down-modulate the response when the foreign attack is over. For decades, immunologists believed that these two characteristics were primarily related to cytokine/chemokine-based communication and cell-to-cell direct contact. More recently, it has been shown that immune cells also communicate by transferring regulatory RNAs, microRNAsin particular, from one cell to the other. Several studies have suggested a functional role of extracellular regulatory RNAs in cell-to-cellcommunicationin different cellular contexts. This minireview focuses on the potential role of extracellularRNAtransfer in the regulation of adaptive immune response, also contextualizing it in a broader field of what is known of cell-free RNAs in communication among different organisms in the evolutionary scale.