Ultrastructural identification of mast cells obtained from human bronchial lumens.

We have investigated the morphology of mast cells in human bronchial lavage fluid. Under light microscopy, these cells were seen to contain discrete metachromatically positive granules that were indistinguishable from those present in mast cells and basophils from other sources. With electron microscopy, the bronchial mast cells were shown to be mononucleated and to contain granules which primarily consisted of particulate materials. Complex structures such as scrolls and crystalloids were also found in the granules. In order to delineate the relationship between bronchial mast cells and mast cells from other anatomic sites, we studied the ultrastructure of tissue mast cells from bronchial, lung parenchymal, and bone marrow biopsy specimens, and that of basophils from peripheral blood. There were similarities as well as differences in these cells from different sources--in their size, shape, lobes of nuclei, nuclear chromatin distribution, and structure of special, presumably histamine-containing, cytoplasmic granules. Based on the electron microscopic data, we believe the intralumenal cells previously described in human beings can be classified as mast cells. The presence of viable, immunoreactive mast cells in the lumen of bronchi may have a significance in relation to respiratory allergic reactions, especially the immediate-type respiratory response.