DETECTION OF PLASMINOGEN-ACTIVATOR INHIBITOR-1 (PAI-1) MESSENGER-RNA IN HUMAN MEGAKARYOCYTES BY IN-SITU HYBRIDIZATION

platelets have been described to contain a large proportion of the cir culating plasminogen activator inhibitor type 1 (PAI-1) which is relea sed on platelet activation. This protein could be taken up by platelet s from the plasma or synthesized by megakaryocytes (MKs). Recently, PA I-1 mRNA has been detected in a human megakaryoblastic leukemia cell l ine (MEG-01) by the polymerase chain reaction (PCR). However, a direct demonstration of its presence in normal human MKs is lacking. In orde r to prove directly the megakaryocytic origin of platelet PAI-1, the M EG-01 cell line, human bone marrow enriched in MKs, and bone marrow sm ears from allogeneic bone marrow transplantation donors were investiga ted for the presence of PAI-1 mRNA using in situ hybridization (ISH). Specimens of bone marrow were first stained with May-Grunwald Giemsa ( MGG) for cell identification according to their morphology. Subsequent ly, the same slides were used for ISH, PAI-1 mRNA was clearly demonstr ated in the MEG-01 cell line and in MKs, and its presence correlated w ith the detection of PAI-1 antigen by immunocytochemistry. PAI-1 mRNA was also detected in morphologically characterized mature granulocytes of marrow samples.