Fig. 1

The melittin-MIL-2 induced proliferation and stronger cytolytic activity of activated lymphocytes. a The IL-2 activity of melittin-MIL-2 fusion protein was tested by its ability to stimulate proliferation of CTLL-2 cells. Various concentrations (8.0, 2.0, 0.5, 0.125 µM) of the fusion protein were incubated for 48 h with 2 × 10⁴ CTLL-2 cells that had been starved of IL-2. One μ Ci of [³H] thymidine was added to the medium for the last 18 h, and cell proliferation was determined by [³H] thymidine incorporation. The same dilutions of rhIL-2 were used as standard. PBS was used as negative control (*p < 0.05). b–e The melittin-MIL-2 induced stronger cytolytic activity of PBMCs, specifically NK cells. b–d Representative standard 4-h ⁵¹Cr-release data were shown against the hepatocellular carcinoma cell line SMMC-7721. When the melittin-MIL-2 (2.0 µM) was used, the cytolytic activity was significantly greater compared with rIL-2 and melittin alone (*p < 0.01) at a 30:1 effector-to-target ratio (E:T). e Enriched T cells (CD4⁺, CD8⁺) and NK cells were cultured for 3 days and tested for cytolytic activity. Increase in cytolytic activity was most notable in NK cells. When the fusion protein (2.0 µM) was used, cytolytic activity of NK cells increased sixfold compared with those cultured with rIL-2 or melittin alone