Objective    To detect the bioactivity of human interleukin-12 (hIL-12) extracted from transgenic potatoes.     Methods    ELISA was used to assess hIL-12induced IFN-γ secretion in peripheral blood mononuclear cells (PBMC) and observe the blocking effect of monoclonal antibody to hIL-12 on the bioactivity of hIL-12. Lethal effect of hIL-12-activated PBMC on NK sensitive K562 cell line was detected by MTT assay. Apoptosis of tumor cells was observed under laser confocal microscope with double Annexin V/PI staining.     Results    The expression of hIL-12 and recombinant hIL-12 (rhIL-12) extracted from transgenic potato leaves or tubers at the concentration of 25 pg/ml to 400 pg/ml induced IFN-γ secretion in PBMC. The mount of secreted IFN-γ was （163.34±22.17）pg/ml to (12 107.10±3 996.51)pg/ml after treated with hIL-12 from potato leaves and was (224.20±25.76)pg/ml to (11 196.30±4 067.48)pg/ml after treated with potato tubers

which was significantly higher than that of commercially available hIL-12 (P0.01). The secreted IFN-γ was almost fully blocked by monoclonal hIL-12 antibody. The apoptotic rate of K562 cells treated with 200 pg/ml hIL-12 extracted from transgenic potato leaves or tubers was (28.4±8.7)% and (32.3±6.9)%

respectively

which was much higher than that of commercially available hIL-12 (P0.05). Laser confocal microscopy showed the characteristic apoptosis of K562 cells at early

middle and late phases after treated with the extracted hIL-12.     Conclusion    hIL-12 extracted from transgenic potato induces PBMC producing IFN-γ and excert antitumor effect on K562 leukemia cells. 