S100A9 and infection: This conclusion was based on the observation that - a) treatment of macrophages (and mice) with S100A9 blocking antibody diminished inflammatory response, while virus replication/infection was unchanged (Figure S5A, S5B and S12A), b) virus replication in S100A9 KO macrophages is reduced compared to WT cells (Figure S7A), and c) addition of S100A9 protein (to mimic extracellular S100A9 protein) to IAV infected S100A9 deficient (KO) cells led to a pro-inflammatory response even in the absence of intracellular S100A9 (i.e. in S100A9 KO BMDMs) (Fig. 4D).