Ultrastructural detection of histamine in human mast cells developing from cord blood cells cultured with human or murine recombinant c-kit ligands.

Immature human mast cells, arising from cord blood mononuclear cells cultured in the presence of the c-kit ligand of human or murine origin, contain mixtures of morphologically immature and mature secretory granules. Use of a new cytochemical technique to localize histamine in ultrastructural samples (based on the affinity of the enzyme, histaminase, for its substrate, histamine) localized this amine to mature mast cell granules of all substructural patterns present, as well as to condensation foci appearing in immature cytoplasmic granules. This cytochemical evidence of histamine bound to condensation foci during granule building in developing mast cells is analogous to evidence obtained during granule recovery of degranulated human basophils and mast cells.