A novel diagnostic method for pulmonary aspiration in a murine model : Immunocytochemical staining of milk proteins in alveolar macrophages

Aspiration of foreign material into the lungs has been implicated in the etiology of a variety of pulmonary disorders. Although aspiration is a common clinical problem, its diagnosis represents a major challenge due to the lack of sensitive and/or specific tests. In this study, we evaluated the sensitivity and specificity of a novel diagnostic method in a murine model of milk aspiration. Under light anesthesia, BALB/c mice received either single or repeated intranasal instillation of milk. Control animals received sterile physiologic saline or were infected with respiratory pathogens in a similar manner. After isolation and cannulation of the trachea, mouse lungs were lavaged with PBS at various time points after the last aspiration event. Cells were recovered for Oil Red O (ORO) staining as well as immunocytochemistry for milk proteins: alpha-lactalbumin and beta-lactoglobulin. After single aspiration of milk, a large number of alveolar macrophages displayed a strong immunoreactivity for alpha-lactalbumin for 2-96 h. After single and repeated aspiration, the percentage of positive cells for alpha-lactalbumin was significantly higher when compared with ORO staining at 24, 48, and 72 h (p < 0.05). No immunoreactivity for milk proteins was found in alveolar macrophages obtained from our control groups. These findings demonstrate that immunocytochemical staining of milk proteins within alveolar macrophages represents a novel, sensitive, and specific test for the diagnosis of aspiration in a murine model.