DDAbs recognized human/rat GPIIIa chimeras containing human amino acid residues at positions 49 to 98.

DDAb 1 reacted with recombinant human (H), chimera H1-98, R99-762, and platelet (PL) GPIIIa but not with chimeras H1-48, R49-762 or H1-48, R49-98, H99-762 in the presence, but not in the absence, of quinine, showing that human sequence at positions 49 to 98 is required for binding. The same pattern of reactions was obtained with monoclonal AP3. Essentially, the same results were obtained with DDAbs 2 and 3 (not shown). No reactions were obtained with the DDAbs in the absence of drug. Human and rat sequences are depicted by closed and open boxes, respectively.