Brefeldin a

Antibodies for flow cytometry analysis were purchased from BioLegend. For the flow cytometry analysis of surface markers, the cells were stained on ice with fluorescence-conjugated antibodies for 30 min according to the manufacturer’s instructions. For the staining of intracellular markers, such as granzyme B, the cells were treated with brefeldin A (InvivoGen, Cat: inh-bfa) at 37 °C for 6 h. Cells were stained with antibodies against surface markers and then fixed and permeabilized using an intracellular staining kit (BD Biosciences, Cat: 559,302, 559,311) at 4 °C for 30 min and then stained with target intracellular antibody at 4 °C for 30 min. Stained cells were finally evaluated by flow cytometry and analyzed using FlowJo Software. The antibodies used for flow cytometry are presented in Supplementary Table 3.

For blocking antibodies, mice were injected i.p. with 250µg of α−CD4 (GK1.5, BioXcell) or 200µg of α-IFNAR (MAR1.5A3, BioXCell) one day before receiving 100 PFU of BrightFlu followed by a second dose at day 4 post infection. For depleting antibodies, mice were injected i.p. with 250µg of α-Ly-6G (1A8, Biolegend) daily for 5 days starting from 1 day prior to BrightFlu. Poly(I:C) was injected intratumorally with 10µg of Poly(I:C)-Rhodamine in 10µl PBS. For intracellular IL-12 staining, mice were injected i.v. with 250µg of Brefeldin A (Invivogen) and tissues harvested 6hr post injection.