Lipid storage disease: Part II. Ultrastructural pathology of lipid storage cells in sphingolipidoses.

The ultrastructural pathology of the stored materials in lipid storage cells, particularly of macrophagic nature, in various disorders of sphingolipidosis was investigated. Cell morphology of the lipid storage cells was largely divided into two groups; one had peculiar cell morphology, such as Gaucher cells or globoid cells, and the other showed the appearance of foam cells. These cytological characteristics of the lipid storage cells were closely related to the ultrastructural configuration of lipid storage inclusions. By transmission electron microscopy, the fundamental structures of the stored materials were classified into two types; tubular and lamellar. The tubular structures were formed by accumulation of ceramide or monohexosyl ceramide, whereas the lamellar structures were formed by accumulation of larger sphingolipids than monohexosyl ceramide. These tubular structures were proven to consist of multilayers of lamellae, which are considered fundamentally similar to the lamellar structures. Almost all the lipid storage inclusions are considered to be of lysosomal origin, because of their encirclement by a single unit membrane and localization of acid phosphatase activity, and participation of heterophagic or autophagic mechanisms as for the development of the inclusions may be noted. Besides, the occurrence of secondary lipid storage was pointed out in some disorders of sphingolipidosis.