Figure 5.

Beij/89 viruses do not differ in their ability to bind to, infect or replicate in murine respiratory epithelial cells. (A) Ability of viruses to bind to and elute from the epithelial cell surface. Duplicate tubes of formaldehyde-fixed LA-4 epithelial cells were mixed with 100 HAU of L (white columns), S (black columns) or Mo (striped columns) viruses for 1 hr on ice. After virus adsorption, one sample was held at 4°C ('4°C') while the duplicate tube was transferred to 37°C for 30 min ('37°C'). A third tube with no cells received virus alone ('control') and was held on ice throughout. Following centrifugation of samples, virus in each of the supernatants was quantified by hemagglutination assay. Data shown are the mean ± 1 SD HAU from 3 independent experiments. (B) Monolayers of LA-4 cells were infected in chamberslides with increasing doses of L, S and Mo viruses as described in Materials and Methods. At 6-8 hrs post-infection cells were fixed and stained via immunofluorescence for expression of influenza virus NP. Data represents the mean percent infection ± 1 SD from 4-8 independent fields per chamber. (C) Release of infectious virus from influenza virus-infected LA-4 cells. Monolayers of cells were infected with L, S or Mo viruses at a multiplicity of infection of 10 PFU/cell and, after 1 hr, washed to remove any unbound virus. Samples of supernatant were removed at 2 hrs and 24 hrs and levels of infectious virus determined by plaque assay on MDCK cells. The fold increase in infectious virus was calculated by dividing the viral titre obtained at 24 hrs post-infection by that at 2 hrs. Data are the mean ± 1 SD from 3 independent experiments.