Detection of anti-GPIIbIIIa and anti-GPIbIX autoantibodies in BM and PB compartments. Cell-bound and free anti-GPIIbIIIa and anti-GPIbIX autoantibodies were detected in BM aspirate (A) and PB samples (B) from ITP patients (n = 18), patients with nonimmune thrombocytopenia (n = 3) and healthy controls (n = 6). The cutoff is indicated by the dotted line at an optical density of 0.21.