SPP1 and influenza: To rigorously investigate this, future studies will require the use of conditional knockout models such as Areg fl/fl-Foxp3 Cre mice or adoptive transfer approaches employing wild-type or growth factor-deficient (e.g., Spp1 or FGF7 null) Tregs, as previously described in influenza [20, 21] and LPS-induced and left-lung pneumonectomy lung injury models [19].