Heterogeneity of bronchial lumen mast cells which are homogeneous by electron microscopy.

Bronchial lumen mast cells were obtained by bronchial lavage from rhesus monkeys and fractionated on a discontinuous metrizamide gradient. Those cells identified as pleomorphic by standard microscopy sedimented in the higher concentrations of metrizamide, while the round cells were dispersed through all gradient fractions. Electron microscopic studies of the pleomorphic and round cells demonstrated that these were morphologically identifiable as mast cells. Although all the cells appear to be mast cells, they are heterogenous in that mast cells in the higher concentrations of metrizamide had higher concentrations of histamine. By contrast, the mast cells in the lower concentrations of metrizamide had greater biologic activity as indicated by greater release of histamine following an immunologic stimulus. The heterogeneity of bronchial lumen mast cells shown by light microscopy, histamine content, and histamine releasibility may be due to the presence of subpopulations of mast cells or changes in a single cell line reflecting differential maturation.