Generation of stat6 −/− and ifnar1 −/− iBMDMs

Tibias and femurs were obtained from ifnar1 ^−/− and stat6 ^−/− mice (C57BL/6 background) and the bone marrow extracted under sterile conditions flushing bones with complete medium (DMEM, GlutaMAX, supplemented with 10% heat‐inactivated foetal calf serum (FCS) and 1% penicillin–streptomycin). Red blood cells were lysed via incubation with ammonium‐chloride‐potassium (ACK) lysis buffer (A1049201; Gibco) for 5 min at room temperature. Cells were then washed in 10 ml of complete medium and passed through a 70‐mm cell strainer (2236348; Fisherbrand) prior to centrifugation. Cell pellet was dislodged before plating on 20‐cm petri dishes (Sarstedt) in complete medium supplemented with 20% syringe‐filtered L929 supernatant, as source of macrophage colony‐stimulating factor, and maintained at 37°C in a humidified atmosphere of 5% CO2. Medium was replaced with fresh medium supplemented with L929 after 1 day of culture. After 5 days, BMDMs were immortalised by exposing them to the J2 CRE virus (carrying v‐myc and v‐Raf/v‐Mil oncogenes, kindly donated by Avinash R. Shenoy, Imperial College London) for 24 h. This step was repeated 2 days later (day 7), followed by continuous culture in DMEM supplemented with 20% (vol/vol) filtered L929 cell supernatant for 4 to 6 weeks. The presence of a homogeneous population of macrophages was assessed by flow cytometry using antibodies for CD11b (1:200, clone M1/70; catalogue number 17‐0112‐82; eBioscience) and CD11c (1:200, clone N418; catalogue number 48‐0114‐82; eBioscience).