Analysis of mast cell activation using diamine oxidase-gold enzyme-affinity ultrastructural cytochemistry

We review a new technique--diamine oxidase (DAO)-gold ultrastructural enzyme-affinity labeling--which we developed to localize histamine in subcellular sites of mast cells. The DAO-gold method showed that isolated human lung mast cells contained abundant histamine in their cytoplasmic granules, a conclusion which was verified by a large number of specificity controls. We also studied mast-cell-rich eyelid lesions which developed in interleukin-4 transgenic mice. The DAO-gold method demonstrated histamine in the electron-dense granules of mast cells in these lesions, but little or no histamine was detected in the swollen, empty granules of mast cells undergoing piecemeal degranulation. This new enzyme-affinity-gold method has permitted the first ultrastructural localization of histamine in subcellular sites of routinely prepared electron microscopy samples. The method has also permitted the first morphological studies of histamine secretion in vivo and has demonstrated that such secretion can be associated with the ultrastructural changes of piecemeal degranulation.