Isolation and culture of human alveolar macrophages AM were isolated from deidentified human donor lungs, which were not suitable for transplantation and donated for medical research. We obtained the donor lungs through the International Institute for the Advancement of Medicine (Edison, NJ) and the National Disease Research Interchange (Philadelphia, PA) [3] . The Committee for the Protection of Human Subjects at National Jewish Health approved this research and has designated this research as non-human project. The isolated AM could be frozen and recovered in 90% FBS and 10% DMSO. There was no apparent difference in response with frozen or freshly isolated macrophages in terms of the level of infection and virus-induced TNF-a secretion (data not shown). AM were plated in DMEM/ 10% FBS with antibiotics, and cultured at 37uC in 10% CO 2 overnight. The cells were then washed and cultured for another day in DMEM and 1% charcoal stripped FBS with antibiotics before viral infection. Their purity was measured by staining for CD68 (Dakocytomation, Carpinteria, CA) [3] .