Given the essential role of NK cell

Given the essential role of NK cells in HBV clearance, NK cell activation after HBV plasmid injection needs further investigation. In our study, NK cells from both the liver and spleen produced more IFN-γ at day 5 after hydrodynamic HBV plasmid injection than after control pAAV plasmid injection (Fig. 3A). This phenomenon coincided with the observation that NK cell depletion reduced the levels of IFN-γ secreted by splenocytes (Fig. 3B). As expected, IFN-γ–deficient GKO mice could not eliminate HBV until 7 wk after HBV plasmid injection (Fig. 3C); moreover, recombinant murine IFN-γ treatment in NK-depleted mice restored their ability to inhibit HBV replication (Fig. 3D). Using a previously reported method in which mice were depleted of NK cells by anti-AsGM1 and then transferred with donor NK cells (2), we found that adoptive transfer of normal WT NK cells, but not NK cells from IFN-γ–deficient GKO mice, might restore the ability of NK-depleted mice to eliminate HBV (Fig. 3E). Taken together, these findings suggest the existence of helper NK cells that are required to promote anti-HBV cellular immunity via IFN-γ production in this mouse model.