A possible mechanism for island formation by rat ascites hepatoma cells with special reference to the function of aggregation factor at the cell surface.

Two tumor cell-aggregation factors of glycoprotein nature, separated from rat ascites hepatoma AH136B cells (forming cell islands in vivo), had different antigenicity; one was not absorbed by immunoadsorbent chromatography with anti-rat serum antibody and the other was. The unabsorbed factor induced aggregation (as shown in the form of simple apposition) of rat ascites hepatoma AH109A cells (present as a free form in vivo) and cell adhesiveness characterized by well-defined tripartite junctional complexes, including intermediate junctions, desmosomes, and tight junctions. In contrast, the absorbed factor from AH136B cells, AH109A cells or normal rat serum aggregated AH109A cells but failed to develop the junctional complexes; only simple apposition was observed. AH109A cells themselves contained the absorbed factor but not the unabsorbed factor. AH136B cells proliferating in the skin developed the junctional complexes, while AH109A cells proliferating in the skin did not from any junctional complexes.