MicroRNAs: the Key Regulators of PRR Signaling

The innate immune system provides the first line of defence against infection. The main molecules involved in recognizing invading pathogens are the Pattern Recognition Receptors (PRRs). They invoke inflammatory responses to eliminate infection. To avoid excessive inflammation and to prevent tissue damage, signalling of these receptors needs to be under stringent control. MicroRNAs (miRNAs) have recently been proved to regulate the innate immune responses. They are evolutionary conserved, genome-encoded small RNAs (~22 nucleotides) that down-regulate gene expression at the post-transcriptional level by either translational repression or by mRNA degradation through binding to the 3′un-translated region (UTR) of their target mRNAs. In this review, we comprehensively discuss the recent understanding of how miRNAs respond to PRR signalling and their role in the initiation and termination of inflammatory responses. Increasing evidence also suggests that both virus-encoded miRNAs and cellular miRNAs have important functions in viral replication and host innate anti-viral immunity.