Use of a photodensitometric technique to quantify microscopic lung lesions in mice: Antiviral activity against swine influenza virus.

During studies of swine influenza virus (A/NJ/76) infection, a technique was devised to quantify the pulmonary lesions in infected mice treated at different time intervals with antiviral chemotherapeutic agents. The technique is based on the premise that as the severity of microscopic change increases, the optical density of lung sections also increases because of edema and increased cell numbers in infected lungs. Seven days after intranasal instillation of the virus, mice were killed and the lungs were perfused with 2% glutaraldehyde at constant pressure. Lungs were processed in a routine manner, sectioned at standard levels, and stained with hematoxylin and eosin. By using standard photomicrography equipment, multiple optical density measurements were made of lung sections in a carefully controlled systematic manner, and a mean optical density was determined for each lung. The optical density of lungs of mice treated before and after infection with amantadine, rimantadine, or ribavirin was significantly reduced compared with that of the lungs of infected, untreated controls. If treatment was delayed until 15 h after infection, amantadine and ribavirin were effective in reducing pulmonary optical density, but rimantadine was without effect. These findings correlated well with mean lung weight of each group; however, the sensitivity of the optical density technique was greater. Subjective scoring of microscopic lesions revealed differences only between infected and uninfected controls. The densitometric method offers promise as a reliable means of objectively quantifying the pulmonary response to a variety of infectious, toxic, and therapeutic agents.