Wild-type FVB/N mice are unusually susceptible to Mycoplasma pulmonis respiratory tract infection

Mice of the FVB/N strain are increasingly used for producing transgenic and knockout mice. Mycoplasma pulmonis infection produces chronic inflammation resulting in extensive tissue remodeling of the respiratory tract of rats and mice. This process to characterized by an influx of inflammatory cells (lymphocytes, neutrophils, macrophages, dendritic cells), angiogenesis and remodeling of airway blood vessels, thickening of the mucosa, mucus production and partial obstruction of the airway lumen, and fibrosis of the airway wall. Different mouse strains differ remarkably in their susceptibility to M. pulmonis infection, as exempified by C3H (relatively susceptible) and C57BL/6 (relatively resistant) strains, taut there are no data on the response of FVB/N mice. The goals of this study were to determine the susceptibility of FVB/N mice to M. pulmonis infection and to document the histotogical changes in the respiratory tract. 8-week old male wild-type FVB/N mice were inoculated intranasally with 1 × 10² to 3 × 10⁴ M. pulmonis organisms (UAB CT strain) and maintained in barrier facilities for up to 4 weeks. We found that FVB/N mice were very susceptible to infection. Only about 45% survived 2 weeks after infection at the highest dose, compared to approximately 80% and 100% survival of C3H and C57BL/6 mouse strains. Loss of body weight (up to 50%) was a good indicator of the severity of airway infection. Infected FVB/N mice showed typical chronic inflammatory changes in the respiratory tract. In addition, by 3 weeks, lung weight had doubled and bronchial lymph node weight had increased 10-fold (P < 0.05). We conclude that FVB/N mice are very susceptible to Mycoplasma pulmonis infection and are a useful model for studying the angiogenesis and mucosal remodeling that occurs in chronic ahway inflammation.