FIG. 6.

att viruses provide heterologous protection against influenza A/California/04/09 (H1N1) virus in DBA/2-vaccinated mice. (A) Body weight in DBA/2-vaccinated mice. Mice were vaccinated with Sw-att, WF-att, or mock vaccinated and challenged with 20 MLD₅₀ of Ca04. Body weight was monitored daily. (B) Lung viral titers in vaccinated/challenged DBA/2 mice. After challenge with Ca04, two mice in each group were sacrificed at days 3 and 6 postchallenge. Lungs were homogenized in 1 ml of PBS, and viral titers were determined by TCID₅₀. (C) Body weight in mice challenged with 100 MLD₅₀ of Sw30 or 20 MLD₅₀ of Ca04 after passive transfer of antibodies from Sw-att-vaccinated animals into naïve animals. Body weight was monitored daily. (D) Lung viral titers in Sw30- and Ca04-challenged DBA/2 mice after passive transfer of Sw-att antibodies. After challenge with Ca04, two mice in each group were sacrificed at day 3 postchallenge. Lungs were homogenized in 1 ml of PBS, and viral titers were determined by plaque assay (Sw30) or TCID₅₀ (Ca04).