IL-12p40 gene-deficient BALB/c mice exhibit lower weight loss, reduced lung pathology and decreased sensitization to allergen in response to infection with pneumonia virus of mice

•IL-12 was more up-regulated in response to PVM in BALB/c than in C57BL/6 mice.•IL-12p40-/- and wild-type neonatal and adult BALB/c mice were challenged with PVM.•IL-12p40-/- mice showed less weight loss than wild-type mice after PVM challenge.•The percentage of regulatory T cells was higher in the lungs of IL-12p40-/- mice.•IL-12p40-/- mice showed greatly decreased allergic sensitization after PVM infection.

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and pneumonia in infants and pneumonia virus of mice (PVM) causes similar disease. BALB/c mice are highly susceptible, while C57BL/6 mice are more resistant to PVM. IL-12 was significantly more up-regulated in response to PVM infection in BALB/c than in C57BL/6 mice. IL-12p40-deficient neonatal and adult BALB/c mice showed significantly less weight loss than wild-type mice after PVM challenge. The percentage of regulatory T cells, as well as IFN-β and IL-18 expression, was higher in the lungs of both neonatal and adult IL-12p40-/- mice. Adult IL-12p40-/- mice also showed enhanced TGF-β and IL-10 expression and reduced inflammatory responses. Furthermore, IL-12p40-/- mice showed decreased sensitization to inhaled cockroach antigen after PVM infection when compared to wild-type mice. In conclusion, these data suggest that a depressed regulatory capacity in BALB/c mice to PVM infection results in enhanced immunopathology and sensitization to allergen.