Cystolytic events and the possible role of germinal cells in metastasis in chronic alveolar hydatidosis.

Two and six week old alveolar cysts of Echinococcus multilocularis were isolated from C57BL/6J and Balb/cJ mice and used to study the cystolytic events mediated by resident inflammatory cells. Ultramicroscopic degenerative changes in these cysts were compared with the ultrastructure of in vitro grown cysts (free of inflammatory cells). Macrophages, eosinophils and neutrophils were found to bind to the laminated layer of plasma membrane of the germinal layer of cysts. Hydrolytic enzymes and eosinophil granules released extracellularly from inflammatory cells at the cyst surface appear to dissolve the laminated layer and produce gaps in the plasma membrane. Macrophages actively phagocytose the granular ground substance of the disintegrated laminated layer. Cystolysis results in the release of germinal cells which measure 6-17 microns, possess nuclei with prominent nucleoli, sparse endoplasmic reticulum, Golgi complexes and oval mitochondria. Based on histologic evidence we believe that germinal cells may be the progenitors of cysts. The possibility that germinal cells may give rise to distant metastatic foci of alveolar cysts, in immunocompromised hosts, is discussed.