THE INTRACELLULAR-DISTRIBUTION OF CELL ORGANELLES IN NATURAL-KILLER-CELLS DURING THE CYTOLYSIS OF BOUND TUMOR-CELLS, WITH SPECIAL REFERENCE TO THE ROD-CORED VESICLES

The secretory function of the natural killer (NK) cells has been considered to be essential for cytolytic activity against their target cells. In this study, the distribution and spatial relationship of various cell organelles which participate in the secretory process, i.e., Golgi apparatus, vesicles, granules and microtubules, were examined ultrastructurally in nontreated and OK-432-activated rat NK cells bound to the tumor cells, with special reference to the rod-cored vesicles which are the most characteristic structure of the NK cells. Rod-cored vesicles and their closely related structures, "empty" vesicles, were derived from the end portion of the Golgi trans cisternae and became accumulated in the central area which was surrounded by the Golgi apparatus, nucleus and contact surface. Some of the vesicles appeared to be further transported to the contact area along the microtubules extending from the centrioles toward the bound targets. The access of the vesicles to the contact surface occurred at that portion where subplasmalemmal actin lattice was thin. The distribution of the dense granules and multivesicular bodies was similar to that of the vesicles, but the area of their occurrence was a little wider. At the outer aspect of the Golgi apparatus was situated the endoplasmic reticulum from which transitional vesicles came to the inner or cis cisternae of the apparatus. The present observations indicate that the cell organelles of the conjugated NK cells are purposefully arranged in the cytoplasm in such order that the generated rod-cored vesicles and "empty" ones are efficiently directed toward the bound tumor cells.