miR-155-SOCS1 as a Functional Axis: Satisfying the Burden of Proof

The importance of individual target genes for miRNA activity has been difficult to establish. In this issue of Immunity , Lu et al. (2015) disrupt the miR-155 binding site in the SOCS1 3′ UTR in the mouse germline and show that this axis is important for T and NK cell function.