While searching for lactic acid bacteria that can restore aging-impaired immune responses, we isolated the Toll-like receptor (TLR) 2/NF-${kappa}B$-activating strain Lactobacillus plantarum HY7712 from kimchi and investigated its immunomodulating effect in whole-body ${gamma}$-irradiated mice. Exposure to HY7712 strongly activated NF-${kappa}B$ signaling in RAW264.7 cells, but inhibited lipopolysaccharide-stimulated NF-${kappa}B$ activation. Moreover, HY7712 protected against the downregulation of interferon (IFN)-${gamma}$ and upregulation of interleukin (IL)-13 caused by ${gamma}$-irradiation in mice. In mice, ${gamma}$-irradiation impaired NK-cell activity against YAC-1 tumor cells, but following HY7712 exposure, the activity of NK cells was restored to 91.5% of the level measured in control mice (p < 0.05). These findings suggest that HY7712 activates the TLR2/NF-${kappa}B$ signaling pathway and protects against the impairment of NK-cell activity caused by ${gamma}$-irradiation or aging.