Figure 2.

Functional modes of secreted (viral) microRNAs (miRNAs). Host‐ and viral‐encoded miRNAs which are transcribed in the nucleus and processed in the nucleus and cytoplasm can be exported from the cell in extracellular vesicles (EVs). Export pathways involve multivesicular endosomes (MVEs) or budding from the plasma membrane. Viral miRNAs when transferred to recipient cells can promote/inhibit infection by regulating gene transcripts. Examples are shown involving viral miRNA transfer to dendritic cells (DCs) or macrophages (MΦ) that can lead to chronic inflammation through the activation of toll‐like receptors (TLRs). Host miRNAs transmitted from infected to uninfected cells can either enhance or suppress viral infections and/or contribute to chronic inflammation. Antiviral immune responses can be suppressed by host miRNAs that target the interferon (IFN) pathway in epithelial cells (Epi) or through inhibition of macrophage activation. On the other hand, host miRNAs can activate the IFN response by suppressing negative regulators of the retinoic acid‐inducible gene I (RIG‐I). Other mechanisms of host defense include the activation of autophagy