Alterations in lung macrophage immune receptor(s) activity associated with viral pneumonia

To evaluate immune-receptor characteristics in populations of pulmonary mononuclear phagocytes during viral pneumonia, free lung cells were obtained from uninfected mice and mice infected 3, 7, 17 and 31 days previously with parainfluenza 1 (Sendai) virus. The percentage of the phagocytes with demonstrable immune-complex Fc receptors remained fairly constant. The phagocytes with cytophilic Fc and complement receptors increased in relation to the development of viral infection and declined following convalescence. The viral pneumonia was associated with a suppression in Fc receptor-mediated ingestion of erythrocytes, with maximum suppression of activity (a decrease of 51% of control values) occurring 7 days after initiation of the infection. In contrast, complement receptor-mediated ingestion was increased on days 7 and 17 of the infection, indicative of the presence of cells with enhanced phagocytic potential. The dynamics of the lung 'phagocyte defense potential' during viral pneumonia parallels the development of increased susceptibility of the lungs to secondary bacterial infection and the subsequent resolution of disease.