Figure 6

Intranasal treatment with SM prevents the development of non-lethal IVA infection in mice. (A) Scheme of the experiment. BALB/c mice were infected with IVA (0.5 LD) at 0 h, marked by an arrow. Infected mice were intranasally treated with vehicle (10% Tween-80) or 5 mg/kg of SM at the indicated time points (∆). On day 5 after infection, mice were weighed and euthanized and lung tissues were collected. (B) Virus titers in the lungs of mice that received intranasal treatment with SM on day 5 after IVA infection. Mean virus titers are shown by the horizontal bars. Dotted line represents the limit of sensitivity of the assay. The difference between SM-treated and Tween treated groups is statistically significant (**p < 0.01). (C) The effect of SM on the lung tissue of IVA-infected mice. Representative histological images of lung tissue of uninfected animals (I-III), IVA-infected animals (IV–VI), IVA-infected animals intranasally treated with 10% Tween-80 only (VII-IX) or with SM in 10% Tween-80 (5 mg/kg) (X–XII). Histopathological analysis revealed that untreated infected mice had severe diffuse pneumonia and severe bronchiolitis/peribronchiolitis, characterized by neutrophil-dominant inflammatory cellular infiltration (VI and IX, arrow). The intranasal administration of SM led to the disappearance of severe inflammatory changes in the lung tissue of infected mice (XII, arrow). Hematoxylin and eosin staining. Original magnification: I, IV, VII, X 100×; II, V, VIII, XI 200×; III, VI, IX, XII 400×. Black boxes show areas that were examined further at a higher magnification.