Cytotoxicity of treated or non-treated NK cells towards K562 cell at ratio of effector NK cell to target K562 cell at 2:1 and 10:1 evaluated by LDH microcytotoxicity assay. G1 is untreated NK cells; G2 is Human rIL-2 treated NK cells; G3 is direct R. korthalsii extract treated NK cells; G4 is indirect R. korthalsii extract treated NK cells. Each value represents the means ± S.E.M. for 3 independent experiments with 3 technical replicates each. The differences between the control group and treated group were determined by one-way ANOVA (*P < 0.05).