Pulmonary macrophage counts in deceased infants: baseline data for further study of infant mortality

Infant lung samples were obtained prospectively at autopsy by medical examiner pathologists in five areas of the United States and regardless of the cause of death. Four sections were examined for each case and were taken from the anterior and posterior aspects of the right and left upper lung lobes. Lung sections were stained with HAM-56 immunostain, which is specific for macrophages. Sixty-one cases were evaluated for the study. Three pathologists independently counted the number of macrophages per 40x field (10x ocular) in 10 contiguous fields near the center of each lung section examined. There was good agreement between pathologists on the average number of macrophages observed in each case. The mean macrophage count for all fields counted was 16.5 per 40x field (range 0-136), and the mean for individual cases was 16 (range 6.6-39.4). There was no observed difference between right, left, anterior, and posterior lung sections. There was a tendency for cases certified as sudden infant death syndrome to show lower macrophage counts than those with other causes of death, but the difference was of only marginal statistical significance. Seven of 10 cases in which infants died after a survival period in the hospital had a mean macrophage count greater than the overall mean of 16 per 40x field. These data suggest that mean pulmonary macrophage counts > 16 per 40x field may be a marker for causes of death other than sudden infant death syndrome or that there was a survival interval. These data may be useful as baseline data for further studies of infant mortality possibly involving pathologic changes in the lungs.