An improved method for quantifying emphysema and establishing a mouse model of emphysema using cigarette smoke exposure and H1N1 influenza virus infection

Rationale: Cigarette smoking (CS) is a major inducer of chronic obstructive pulmonary disease (COPD) in humans. Due to its relevance in human disease, the present study was designed to establish a mouse model of COPD using H1N1 virus. Further, because quantification of emphysema is labor intensive, we developed a semi-automated rapid model to quantify emphysema.

Methods: C57BL/6 mice at 8-10 weeks were exposed to 150 mg/m3 CS particulate matter for 6 days/week, 2 hours/day, over 4 weeks. Following exposure to CS or room air (RA), mice were infected by intranasal instillation with the influenza A/California/07/2009 H1N1 strain (H1N1) at 500, 200, and 100 plaque forming units (PFU). Experimental groups exposed to RA+PBS, CS+PBS, RA+H1N1, and CS+H1N1 at 14 days post-infection were compared. Inflammation was evaluated in the right lungs after bronchoalveolar lavage, and emphysema was quantified from systematically taken random images of the hematoxylin- and eosin-stained tissue sections of the left lungs.

Results: Infection of mice with 500 pfu H1N1 caused extensive tissue inflammation and emphysema in both RA+H1N1 and CS+H1N1 groups. To minimize H1N1-induced tissue damage, we reduced the titer to 200 pfu and found significantly higher total leukocytes and macrophages in the CS+200H1N1 group. MLI was also increased in the RA+200H1N1 group compared with the RA+PBS, RA+H1N1, or CS+PBS groups. Further reduction of the H1N1 titers to 100 pfu resulted in CS+100H1N1 group still showing significantly more emphysema compared with the other three groups.

Conclusions: We describe an improved semi-automated MLI method that drastically reduced the time required to process and measure air space enlargement. Further, we have established a mouse model of COPD that uses a human-relevant virus to cause emphysema. These results suggest that CS sensitizes the lungs to influenza-induced injury at much lower virus titers.
Funding source: RO1HL068111 and R01HL140839