Inhibitory effects of anti-integrin antibodies, used alone or in combination, on Sc-1 (A) and Ci-1 (B) cell adhesion to intact fibronectin and its cell-binding domains: P1D6, anti-5 (identical results were obtained with the anti-5β1 MoAb JBS5); HP2-1, anti-4; 4B4, anti-β1; and Act-1, anti-4β7. To determine the optimal inhibitory concentration of each antibody, antibodies were individually titrated in independent tests and found to be optimally active at 1 to 3 μg/10⁶ cells. (C) Relative strength of substratum adhesion estimated for Sc-1 cells binding to the 38-kD fragment or 110-kD polypeptide in the presence or absence of either MoAb 4B4 or MoAb Act-1, as determined by exposing bound cells to the centrifugal forces indicated on the abscissa.