Freeze-etch studies of the granules of human mast cells and eosinophils

Abstract

Human tissue mast cells from the skin biopsy of a patient with systemic mast cell disease, and blood eosinophils from two patients with eosinophilia were studied using freeze-etching. The mast cells contain prominent and densely packed cytoplasmic granules which vary widely in size. Favorable cleavage planes visualize subgranular cylindrical or scroll-like lamellae. These lamellae are composed of parallel lines with a repeating unit at ∼140 A. Likewise, some granules of eosinophils contain crystalline inclusions composed of a lattice work of parallel rows of particles. The rows have a periodicity of ∼78 A. It has been previously suggested that the inclusions seen in the granules of mast cells and eosinophils by thin-sectioning techniques might represent artifacts introduced during processing. We observe similar subgranular inclusions using freeze-etching. The demonstration of these lamellar and crystalline inclusions by two different morphologic techniques suggests that they are functional components of the secretory granule and not processing artifacts.