ABSTRACT
The cytoplasmic granules can be isolated by conventional cell fractionation procedures in relatively homogenous forms. Perforin 1 is the pore-forming protein of cytolytic granules. Electron miscroscopical analysis of membranes lysed by isolated granules or by intact killer cells showed the presence of a second pore-forming complex named poly P2. Evidence that cytolytic granules mediate DNA degradation in target cells is still preliminary at the present time. Secretory granules in many cells have been shown to contain proteoglycans. The function of proteoglycans is believed to allow the condensation and packaging of various granule- associated proteins in the granule compartment at high concentrations. Cytolytic granules contain numerous proteins whose known properties are consistent with an important function of granules in cell-mediated cytolysis. Granule factors such as esterases and/or lymphotoxin- like factors may enter the target cell through the pore shown in the upper right panel or, perhaps more likely, through endocytotic mechanisms.
