Fig 1.

In vitro and in vivo characterization of M1 triple mutants. The replication kinetics (MOI, 0.002) (A) and temperature-sensitive (ts) phenotype (B) were determined in MDCK cells by plaque assay. A cold-adapted A/WSN/34 mutant (mu-rWSN) was used as a ts control. BALB/c mice were inoculated i.n. with wild-type A/WSN/33 (wt-WSN) or M1 triple mutants at 5 × 10⁴ PFU/50 μl/mouse. (C) Lung virus titers (n = 3 mice/group) were determined by plaque assay on day 3 postinfection (p.i.). (D) wt-WSN-specific serum HA inhibition (HAI) titers were determined at 4 weeks p.i. (n = 8 mice/group). Because all wt-WSN-infected mice died within 2 weeks of infection, no HAI titers were available for this group.