Immune cell profile in infants' lung tissue.

Little is known about the normal immune cell profile in the lungs of infants without pulmonary disease. Normal lung samples obtained at autopsy of 10 infants that died either due to incidental or inflicted causes or non-pulmonary diseases were stained for antibodies against B and T lymphocytes, macrophages, NK cells, cytotoxic cells, dendritic cells and mast cells. Cells were quantified in the airway epithelial layer, inner layer (between the epithelium and the outer smooth muscle border), outer layer (between the outer smooth muscle border and the external limits of the airway) and alveolar septa. Basement membrane or alveolar septa lengths were assessed by image analysis. Results were expressed as cells/mm. The median age of patients was 6.8 months, ranging from 11 to 840 days. The inner layer of the airways was the region with the smallest density of cells. There was a predominance of cells related to the innate immunity such as CD56+, Granzyme B+ and CD68+ cells in the epithelial layer and alveolar parenchyma. The outer layer and the lung parenchyma presented the highest cellular density. There were very few CD4+ T cells or dendritic cells in most of the lung compartments. The numbers of CD3+ T and granzyme B+ cells correlated positively with age. There was a compartmentalization of immune cells along airways and parenchyma, which may be related to the development of innate and acquired lung defense mechanisms.