PBMCs from disease control donors rarely proliferate when stimulated with peptides from the GPIIIa sequence. Shown here are proliferative responses of PBMCS from representative patients with aplastic anemia C26 (A), C27 (B), C28 (C), and C29 (D) against the panel of 86 peptides spanning the GPIIIa molecule. The dashed horizontal line denotes the level of proliferation taken as representing a significant positive response (SI > 3).