Modulation of agglutinability by alteration of the surface topography in mouse ascites tumor cells

Factors involved in controlling agglutinability of cells with plant lectins include number, distribution, availability and mobility of cell surface lectin receptor sites. We have examined the concanavalin A (ConA)-mediated agglutination of mouse sarcoma 180 ascites tumor cells in the presence or absence of cytochalasin B (CB) using a quantitative electronic particle counter assay. These cells become substantially more agglutinable after brief treatment with low concentrations of CB. Scanning and transmission electron microscopy indicate that CB causes formation of large, broad, cell surface ruffles and loss of narrow projections that appear to be microvilli. Studies using fluorescent ConA suggest that lectin receptor sites concentrate on these ruffles and that the ruffles seem to directly mediate increased agglutinability in this system. Electron spin resonance studies suggest that CB does not alter lipid “fluidity” in these cells. The results indicate that the gross cell surface topography favoring high agglutinability is one displaying broad ruffles, not numerous narrow projections.