Single-chain antibody MAN-1–derived peptides and circular MAS-1– and MAS-2–derived peptides specifically inhibit adhesion, which is mediated by the activated Mac-1 integrin. (A) MAN-1 inhibits adhesion of PMA-activated monocytes but not nonactivated monocytes to immobilized fibrinogen under flow conditions. An activation-nonspecific CD11b antibody (clone 2LPM19c) inhibits both activated and nonactivated monocytes. (B) Inhibition of adhesion of Mac-1–expressing CHO cells on immobilized fibrinogen by circular MAS-1– and MAS-2–derived peptides under flow conditions. For all flow experiments, means and standard deviations of adhering cells based on the counting of 5 visual fields are given. Representative examples of at least 6 experiments are demonstrated.