Epithelial rests of Malassez in vitro. Phagocytosis of collagen and the possible role of their lysosomal enzymes in collagen degradation.

Cells from porcine epithelial rests of Malassez were cultured in vitro with collagen prepared from rat tail tendons. Serial sections of the cultures were prepared for examination in the electron microscope. Some of the material was processed to demonstrate activity of acid phosphatase. Electron microscopy showed that the epithelial cells had phagocytosed collagen in vitro, and study of the serial sections indicated that much of the phagocytosed collagen was contained wholly within the cells. Reaction product indicating sites of acid phosphatase activity was found to be associated with intracellular collagen, and some of the intracellular fibrils exhibited nonsymmetrical loss of material and also localized loss of banding, suggesting intracellular digestion of collagen. A lysosomal fraction was prepared from epithelial cells cultured from the rests of Malassez, and this was shown using biochemical assays to contain activities of thiol-dependent cathepain, cathepsin D, beta-D-glucuronidase, aryl sulfatase, and acid phosphatase. The lysosomal fraction had the capacity in vitro to depolymerize and digest collagen obtained from rat tail tendon. It was concluded from these observations and results that epithelial cells cultured from the rests of Malassez can digest collagen in vitro. The findings suggests a possible mechanism whereby the epithelial cells can destroy the extracellular substance of connective tissue during their well known participation in cyst formation in vivo.