(A) Sc-1 and Ci-1 cell adhesion to 38-kD fragment and 110-kD polypeptide with and without addition of the anti-β1 activating antibody TS2/16. Data are presented as the ratio of cells bound to each of the two proteins when compared with cells adhering to the intact fibronectin molecule, after subtraction of nonspecific binding to BSA (5% to 10%). The extent of cell attachment was analyzed at various concentrations of the fragment/polypeptide and is expressed as molar equivalents of intact fibronectin. (B) Relative avidity of Sc-1 and Ci-1 cell binding to the 38-kD fragment and 110-kD polypeptide assessed by applying increasing centrifugal forces to detach the adherent cells.