Comparison of lung histopathology and bronchoalveolar lavage cytology in mice and cotton rats infected with respiratory syncytial virus.

Lung histology as well as cell number and size distribution in bronchoalveolar lavage (BAL) were compared in Balb/c mice and in cotton rats, of various immune status regarding the respiratory syncytial virus (RSV), when subjected to challenge with RSV. In mock-immunized animals, RSV infection typically caused microscopic inflammatory lesions of the lungs and the presence of inflammatory cells in the BAL. Immunization with a formalin inactivated vaccine prior to challenge increased the severity of the lung lesions and the number of cells recovered in the BAL. We observed that cotton rats are more convenient to study primary RSV infections, inasmuch naive subjects show more pronounced lesions than do naive mice. Conversely, the changes in lung histopathology and in BAL cytology associated with exposure to formalin inactivated vaccine prior to challenge were more apparent in mice, making them a more suitable model for potentiation studies. Moreover, mice showed less individual fluctuations than cotton rats. The reading of the lung sections could be made less tedious by use of computer image analysis, which results paralleled those of conventional examination. In mice, cytological analysis of the BAL could be used in place of lung histology for some potentiation studies since the number of cells recovered in BAL reflected the intensity of the lung lesions and size distribution profiles typical of potentiation were recognized.