HVEM signaling mediates LIGHT-induced NK-cell activation. (A) HVEM is expressed on the surface of NK cells. NK cells from Rag1^-/- or Hvem^-/- mice were enriched by NK purification kits and then stained with anti–NK1.1-conjugated PE and biotin-labeled anti-HVEM followed by streptavidin-APC. Data are representative of at least 3 independent experiments. (B) Anti-HVEM mAb blocks LIGHT-mediated NK-cell IFN-γ production and proliferation (data not shown). Different doses of anti-HVEM antibody were added to rLIGHT-treated NK-cell culture for 3 days. ³H-TdR incorporation and IFN-γ assays were described previously. Anti-HVEM antibody can significantly inhibit rLIGHT-mediated stimulation (P < .001). (C) Hvem-deficient mice impair LIGHT-mediated IFN-γ production by NK cells. NK cells from Rag1^-/- or Hvem^-/- mice were stimulated with different amounts of rLIGHT with assessment as above. Hvem^-/- mice showed reduced response to rLIGHT (P < .001). The results are representative of 6 independent experiments. Data analysis was performed by using the Student t test. Averaged results are expressed as mean plus or minus SD.