IL-15 complexes (IL-15c) were generated on the day of use by incubating 1.5 mg recombinant mIL-15 with 7 mg IL-15Ra Fcchimera (R&D Systems, Minneapolis, MN) at 37uC for 20 minutes followed by 4uC for at least 10 minutes. For Ra only controls, 7 mg IL-15Ra Fc-chimera (R&D Systems, Minneapolis, MN) was incubated similarly to complexes without addition of the cytokine. Complexes or Ra alone were administered via passive inhalation into both nostrils using a micropipette delivering 36.25 mL (for daily treatments) or 72.5 mL (for one time treatments) of complexes in sterile PBS. For assessment of cell proliferation, animals received 2 mg of BrdU (Sigma-Aldrich, St. Louis, MO) administered i.p. in a 200 mL volume of PBS. Cells were isolated from these animals 12 hours after treatment and stained with 20 mL aminoactinomycin D (7-AAD; BD Pharmingen, San Jose, CA) for 20 minutes at 4uC. Cells were surface stained as previously described and stained intracellularly with FITC-labeled anti-Ki-67 and APC-labeled anti-BrdU monoclonal antibodies (BD Pharmingen, San Jose, CA) according to manufacturer's instructions.