Exosome-derived miRNAs and cellular miRNAs activate innate immunity.

Circulating exosome-containing small RNAs have been demonstrated in vitro to be taken up by recipient cells and to alter gene expression through RNA interference. Here, we show that exosomes purified from various cancer cell lines as well as gel-purified exosomal and cellular miRNAs can induce pro-inflammatory cytokine expression in human peripheral blood mononuclear cells. Thus, circulating miRNAs may trigger innate immunity via pathogen recognition receptors, a new miRNA-activated pathway that merits some consideration.