Importance of cell-to-cell contact and transfer in white cell activity

Formation of cell junctions and the occurrence of cell-to-cell transfer through these was examined in mixed cultures of PK 15 pig kidney and mouse peritoneal cells. Under standardized conditions of experiment, a close contact developed between peritoneal and target cells within 90 min. Light and scanning electron microscopic examinations of the area of close contact indicated extension of cytoplasmic processes from peritoneal cells towards the nucleoli of target cells. The size and localization of the nucleolus and the incorporation of a considerable amount of label by the nucleolar associated chromatin also indicated the decisive role of the nucleolus in the events following upon the establishment of close contact. Autoradiographic examinations showed that part of the 6-3H-thymidine labelled material migrated from the nucleus of target cells into the cytoplasm of peritoneal cells within 30 min. A greater cytoplasmic accumulation of label took place in peritoneal cells exclusively in the presence of actinomycin-D, indicating a rapid breakdown of transferred material under normal conditions. The development of cell-to-cell contact and transfer was found to depend greatly on the composition of the nutrient medium.