These results suggest that perlecan, which is abundantly produced and accumulated in the cyst wall of immature granulation tissue, traps Ox-LDL locally, and that Ox-LDL is phagocytosed by macrophages. Thus, LDL-laden foamy macrophages are aggregated in the granulation tissue, and free cholesterol from ruptured macrophages may be concentrated locally to be crystallized, which may induce foreign body granulomas in the cyst wall.

In order to determine the role of the basement membrane-type heparan sulfate proteoglycan (HSPG), known as perlecan, in the formation of the characteristic cribriform 'structures of salivary adenoid cystic carcinomas, the mode of expression of mRNA for the core protein of HSPG was investigated by using in situ hybridization (ISH) both in surgical specimens and in a cell system (ACC3) of adenoid cystic carcinomas. In the surgical specimens, the mRNA for the HSPG core was more intensely expressed in solid tumor cell nests, especially in smaller ones. Within the nests, the signals were detected almost exclusively in cuboidal cells forming small pseudocysts. In contrast, signals were absent in flat cells forming large pseudocysts or in carcinoma cell nests attaching to the peripheral nerves or blood vessels. In normal salivary gland tissues, myoepithelial cells expressed the mRNA at a high level, but acinar and duct epithelial cells did not. In the time-course experiment of ACC3 cells, signals for HSPG core increased with time and reached the maximum on day 4, decreasing thereafter in a culture condition in which cells reached confluence in a week. The results indicate that HSPG is biosynthesized by adenoid cystic carcinoma cells which are in the proliferation phase, and that tumor cells producing HSPG tend to form initial structures of stromal pseudocysts.

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