(a) C57Bl/6 mice were seeded with B16 tumors subcutaneously (SC). After 10 days, (when tumors were typically 0.5–0.6cm in the longest diameter), the mice were injected intraperitoneally with rhIL-2 at 75,000U/injection three times a day for 3 days. On the fourth day, a single further injection of IL-2 was given. (b) Forty-eight hours after the final injection of phosphate-buffered saline (PBS) or IL-2 (in a), vascular leakage into the lungs was measured34 (n = 4; representative of two separate experiments). (c) C57Bl/6 mice treated with intraperitoneal injections of either IL-2 or PBS (as described in a; three/group) were killed 48 hours after the last injection. Immune cells positive for the markers shown are plotted as a percentage of CD45+ gated cells. NK cells, natural killer cells; NKT cells, NK T cells; rhIL-2, recombinant human IL-2.