Cytoplasmic crystalloids in irradiated rat parotid glands

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Abstract
Cytoplasmic crystalloids were found in parotid acinar cells of rats given a large (6400 R) single exposure of X-rays to the head and neck. The crystalloids were first observed 1 day after irradiation and became numerous at 3-4 days. They were associated with autophagic vacuoles, which were seen in acinar cells as early as 3-6 h. Crystalloids sometimes appeared to be forming within autophagic vacuoles, which also contained membranous residues and apparently degenerating secretory material. They were bounded by a single, smooth membrane and had a substructure consisting of dense, parallel longitudinal striations. The crystalloids were also seen in macrophages associated with the basal surfaces of acinar cells. At 3-4 days macrophages were numerous and many contained crystalloids, degenerated secretory droplets and other cellular debris, which they apparently had phagocytosed. By 6-8 days crystalloids and macrophages were seen infrequently. Regarding mode of formation, removal by macrophages and ultrastructure, the crystalloids resembled those described by others after ethionine intoxication. Ethionine-induced crystalloids have cytochemical characteristics consistent with a lysosomal identity. The crystalloids in irradiated parotid glands probably reflect a variant type of lysosome, which is a nonspecific manifestation of severe cellular injury and can be elicited by a variety of injurious agents.