TF and cystic fibrosis: Next, to assess if increased iron availability during coculture with CF AECs impacts S. aureus biofilms, we performed biofilm assays on CF AECs in the absence of virus infection and added exogenous free iron (FeCl3), non-iron-bound transferrin (apotransferrin [apo-TF]), and iron-bound transferrin (holotransferrin [holo-TF]) (Fig. 6B).