A fine structural analysis of surface interactions of agglutinated sarcoma 180 cells

Sarcoma 180, a mouse ascites tumor, was examined ultrastructurally using transmission electron microscopy. Its general fine structure, and the cell surface interactions occurring as a result of agglutination were examined. Three types of agglutinins were used, Concanavalin A (Con A), an ascites "factor", and manganese ion. Ultrastructurally, Sarcoma 180 had the features of many tumors: A large heterochromatic, multilobate nucleus with numerous nucleoli, reduced amounts of endoplasmic reticulum, and numerous microvilli on the cell surface. The mitochondria were somewhat pleomorphic. Large lipid droplets were seen in addition to several other large, darkly stained bodies in the cytoplasm. Cell surface interactions between untreated cells were not commonly seen. Three surface interactions were seen after agglutination: 1) Microvillous associations characterized by the interaction of villi with adjacent cell surfaces; 2) intermediate associations in which adjacent cell membranes were approximately parallel, crosslinked by patches of lightly stained material, and separated by greater than 100A; and 3) close association in which the cells were separated by less than l00A, commonly 20A, and resembled gap junctions. All three types of associations were seen after Con A agglutination. The intermediate association may represent actual crosslinking by Con A aggregates. The close associations, it was argued, resulted from interactions between cell surface components. Microvillous associations were most commonly seen, though their significance was not clear. The ascites "factor" at high concentration induced pinocytosis and vacuolization. Agglutination resulted from large aggregates of flocculent material crosslinking the cells. At lower concentration, intermediate associations were seen, small aggregates of "factor" possibly crosslinked the cells together. Manganese ion produced a very rapid agglutination mediated totally by villous interactions. Points of interaction were very tight, with no obvious gap between membranes. It was thought that ionic bridging, or denaturation of surface components was involved.