Ribosomes and secretory granules in human mast cells: close associations demonstrated by staining with a chelating agent

The distribution of ribosomes was investigated in mature human mast cells with a chelation‐based staining protocol known to bleach DNA‐rich structures, leaving RNA‐rich structures unbleached. With this method, electron‐dense ribosomes were adjacent to, attached to, and within secretory granules, which were also bleached with the chelation method that we used. The finding of these ribosome–secretory granule relationships suggests that secretory granules in mature human mast cells may participate in RNA metabolism. This work was supported by a grant (AI 33372) from the National Institutes of Health. We thank Peter K. Gardner for editorial assistance in the preparation of the manuscript and Patricia Fox for printing the electron micrographs.