Pulmonary Inflammation in Brown Norway Rats: Possible Association of Environmental Particles in the Animal Room Environment

Abstract

Brown Norway (BN) rats have been found to develop granulomatous pneumonia with high spontaneous incidence under normal husbandry conditions. In our laboratory, ambient particles from the animal housing environment were suspected to be involved in the pathogenesis of these pulmonary lesions. In the present study, we correlated the histopathology of spontaneous granulomatous pneumonia with the cytology of bronchoalveolar lavage fluid (BALF) analysis and animal room particle counts. The results show that the sum of the macroscopic lesion score in the lung correlated with the number of eosinophils in the BALF. Microscopically, the severity of granulomatous lesions was significantly correlated with both pulmonary eosinophils and the number of eosinophils in the BALF, but not with those of neutrophils or lymphocytes. In addition, the histological features of the lesions were not influenced by housing conditions or sensitization with ovalbumin. Ambient particles (0.3-1.0 μm in diameter) in the animal room environment were measured and compared with the number of eosinophils in BALF. Interestingly, there was a significant correlation between them, suggesting a possible relationship between environmental particles and the pathogenesis of granulomatous pneumonia in BN rats. However, further study is needed to clarify the pathogenic mechanism.