The transcription factor NF-κB regulates the expression of a broad number of genes central to immune and inflammatory responses. We identified a new molecular network that comprises specifically the NF-κB family member NF-κB1 (p50) and miR-146a, and we show that in mast cells it contributes to the regulation of cell homeostasis and survival, while in T lymphocytes it modulates T cell memory formation. Increased mast cell survival was due to unbalanced expression of pro- and antiapoptotic factors and particularly to the complete inability of p50-deleted mast cells to induce expression of miR-146a, which in the context of mast cell survival acted as a proapoptotic factor. Interestingly, in a different cellular context, namely, human and mouse primary T lymphocytes, miR-146a and NF-κB p50 did not influence cell survival or cytokine production but rather T cell expansion and activation in response to T cell receptor (TCR) engagement. Our data identify a new molecular network important in modulating adaptive and innate immune responses and show how the same activation-induced microRNA (miRNA) can be similarly regulated in different cell types even in response to different stimuli but can still determine very different outcomes, likely depending on the specific transcriptome.