Summary
Platelets have been described to contain a large proportion of the circulating plasminogen
activator inhibitor type 1 (PAI-1) which is released on platelet activation. This
protein could be taken up by platelets from the plasma or synthesized by megakaryocytes
(MKs). Recently, PAI-1 mRNA has been detected in a human megakaryoblastic leukemia
cell line (MEG-01) by the polymerase chain reaction (PCR). However, a direct demonstration
of its presence in normal human MKs is lacking.
In order to prove directly the megakaryocytic origin of platelet PAI-1, the MEG-01
cell line, human bone marrow enriched in MKs, and bone marrow smears from allogeneic
bone marrow transplantation donors were investigated 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. Subsequently,
the same slides were used for ISH. PAI-1 mRNA was clearly demonstrated in the MEG-01
cell line and in MKs, and its presence correlated with the detection of PAI-1 antigen
by immunocytochemistry. PAI-1 mRNA was also detected in morphologically characterized
mature granulocytes of marrow samples.
