Infection of human type II pneumocytes with human influenza viruses. (A) Purified alveolar epithelial cells were fixed and analyzed by immunofluorescent staining specific for influenza virus nucleoprotein (×150). (B) The influenza M-gene mRNA profiles were assayed after infection. The concentrations of M-gene mRNA were normalized to those of β-actin mRNA in the corresponding sample. Means of duplicate assays are shown. (C) Alveolar epithelial cells were infected with human influenza viruses and the infectious virus yield (log10TCID50/ml) was determined in aliquots of supernatant collected at various times. Data are the means and the standard errors of independent experiments from three separate donors.