Cell Biology International Reports, Vol. 4, No. 11, November 1980 1031 VISUALIZATION OF CELL-SUBSTRATUM ADHESION PLAQUES BY ANTIBODY EXCLUSION Frederick Grinnell Department of Cell Biology University of Texas Health Science Center Dallas, Texas 75235 ABSTRACT. We report on an antibody exclusion method for detecting cell adhesion plaques. Substrata coated by plasma fibronectin (pFN) appeared uniformly fluorescent when analyzed by indirect immunofluorescence using a specific anti-pFN antibody. When cells that had spread on the substrata were permeabilized and analyzed by indirect immunofluorescence, areas of non-fluorescence were apparent beneath the cells and in focal streaks along the cell margins. The nonfluorescent focal streaks were coincident with adhesion plaques visualized by interference reflection microscopy. INTRODUCTION. Adhesion plaques are believed to be specialized regions of cells involved in cell-substratum attachment. They were first identified with fibroblasts by electron microscopy (Abercrombie et al., 1971; Brunk et al., 1971) and later studied -- -- by interference reflection microcopy (Izzard and Lochner, 1976). In general, they are characterized as sites of close (10 nm) approach of the plasma membrane to the substratum. There is a fuzzy coat on the cytoplasmic surface of the plasma membrane into which microfilament bundles usually insert (Heath and Dunn, 1978). Research in this laboratory has been concerned with cell-substratum adhesion, and in particular, with the role of plasma fibronectin (pFN, cold insoluble globulin) in adhesion (Grinnell, 1978). In the presence of plasma fibronectin, material surfaces (e.g. plastic, glass) become coated with a monomolecular layer of adsorbed fibronectin molecules within seconds after exposure (Grinnell, 1978; Hughes et al., 1979). Binding of pFN to the surfaces is very difficult to reverse with detergents or a variety of other chemical reagents (Grinnell and Minter, 1979). When analyzed by indirect immunofluorescence with a specific anti-pFN antibody, the adsorbed pFN appears as a continuous, uniformly bright fluorescent field (Grinnell and Feld, 1980). While carrying out studies on the distribution of the fibronectin antigen during fibroblast adhesion, observations were made indicating that adhesion plaques might be detectable by an 0309-1651/80/111031-06/$02.00/0 0 1980 Academic Press Inc. (London) Ltd