SIMULTANEOUS MEASUREMENTS OF MEGAKARYOCYTE-ASSOCIATED IGG (MAIGG) ANDPLATELET-ASSOCIATED IGG (PAIGG) IN CHRONIC IDIOPATHIC THROMBOCYTOPENIC PURPURA

We have simultaneously measured platelet-associated IgG (PAIgG) and me gakaryocyte-associated IgG (MAIgG) in 30 untreated patients with chron ic idiopathic thrombocytopenic purpura (CITP). Megakaryocytes were pur ified from bone marrow by 35% Percoll gradient centrifugation, followe d by negative immunopanning using magnetic immunobeads. The normal ran ge of MAIgG in 30 healthy donors was 15.5 +/- 10.0 ng/10(5) megakaryoc ytes, whereas MAIgC in the 30 CITP patients was 140 +/- 59.3 ng/10(5) megakaryocytes, although the values were widely distributed. From the PaIgG and MAIgG data, CITP patients were classified into three types; type I (PAIgG < 200 ng/10(7) platelets and MAIgG < 150 ng/10(5) megaka ryocytes), type II (PAIgG > 200 ng and MAIgG > 150 ng), and type III ( PAIgC < 200 ng and MAlgG > 150 ng). Patients with types I and III had good clinical courses, but, in contrast, patients with type II respond ed poorly to steroid therapy followed by splenectomy or became refract ory to treatment. In splenectomized patients. MAIgG of responder was p romptly decreased to normal range and, in contrast, that of non-respon der was persistently elevated. These results indicate that anti-platel et autoantibodies are able to bind with megakaryocytes in the bone mar row as well as with platelets in the peripheral blood, and the results also suggest that megakaryopoiesis in CITP is heterogeneous. Simultan eous measurement of PAIgG and MAIgG may predict the clinical outcome o f CIPT.