Figure 1. Schedule for the animal experiments.

We conducted three types of experiments to determine the prophylactic effects of b240 administration on pathogenesis and host responses in mice. In all experiments, mice were orally mock-administered with saline or administered with heat-killed Lactobacillus pentosus b240 at a dose of 10 mg/mouse daily for 21 days prior to infection and for 14 days after infection or mock infection. (a) To define the prophylactic effect of b240 administration on mouse survival, mice were infected with 0.3 or 10 MLD₅₀ of mouse-adapted CA04 virus on day 21 post-b240 administration and mortality and morbidity were observed for 14 days post-infection. (b) To define the effects of b240 administration on virus replication, histopathology, cytokine expression, and gene expression, mice were infected with 10 MLD₅₀ of CA04 virus on day 21 post-b240 administration and euthanized on days 1, 3, and 6 post-infection. Their lungs were subjected to virus titration, histopathological examination, cytokine measurement, and microarray analysis. (c) To investigate the immune responses induced by b240 administration in the lungs of mice, mice were mock-infected with PBS on day 21 post-b240 administration and euthanized on days −7, 0, 1, 3, and 6 post-infection (14, 21, 22, 24, and 27 post-b240 administration). Their lungs were subjected to cytokine measurement and microarray analysis.