Transmission electron microscopy of αIIbβ3 oligomers observed in the presence of Mn²⁺. (A) Most frequently, dimers were observed with 1-tail or 2-tail touching. (B) There were fewer integrin trimers. (C) Tetramers and larger oligomers were rare. (D) Size distribution of αIIbβ3 oligomers. These data were fit to an exponential function using Microsoft Excel. (A-C) Magnification, × 170 000.