Haematologica 2004;89: supplement no. 8 - Supplements ...

22Oral CommunicationsCO-006EXPRESSION OF PAR1 ON HUMAN CD133 + CORD BLOOD CELLSAND DURING MEGACARYOCYTE DIFFERENTIATIONDe Candia E,* Rutella S,° Bonanno G, #De Cristofaro R,* Leone G,° Landolfi R,* Scambia G #*Istituto di Medicina Interna e Geriatria,° Istituto diEmatologia, # Istituto di Ginecologia e Ostetricia,Università Cattolica del Sacro Cuore, RomeThe G protein-coupled receptor PAR1 is expressedon platelets, megakaryocytes (MK) and endothelialcells. Whether PAR1 is an early or late marker of theMK maturation is not known. We measured theexpression of PAR1 during in vitro MK maturationand compared it to that of the MK-restricted proteinsGpIIb and GpIb. Human cord blood CD133 +progenitor cells were purified by an immunomagneticseparation system (MACS: Myltenyi Biotec) andcultured under serum-free conditions in the presenceof 10-50-100 ng/mL thrombopoietin (TPO) orSCF 10 ng/mL + TPO 10 ng/mL. Expression of PAR1,GpIIb and GpIb on cultured cells was evaluated atday 0, 5, 7 by using, respectively, PE- PERCP- or FITCconjugatedanti-PAR1 SPAN12, anti-CD 41 and anti-CD 42b MoAbs and flow cytometry analysis. At day0, 70% of freshly purified CD133 + cells showed lowexpression of PAR1, whereas the other antigenscould not be detected. At day 5 of culture PAR1expression was markedly downregulated, beingdetectable in only 15% of total cells, 20% of totalcells expressed the GpIIb whereas the GpIb wasalmost undetectable (Figure 1). At day 7 the expressionof these markers was 35% of total cells forPAR1, 53% of total cells for GpIIb and 20% of totalcells for GpIb. The kinetics of protein expression wassimilar in all culture conditions; interstingly, cell culturedin the presence of TPO + SCF downregulatedthe expression of all the differentiation markers.These results demonstrate that PAR1 is present onthe surface of very early hematopietic progenitorsand that during MK differentiation it is first downregulatedto become later a specific marker of MKmaturation.CO-007POLYMORPHONUCLEAR LEUKOCYTE-PLATELET INTERACTIONIN PATIENTS WITH ESSENTIAL THROMBOCYTHEMIA ANDPOLYCYTHEMIA VERAFalanga A, Marchetti M, Vignoli A, Balducci D,Barbui TDept. Hematology, Ospedali Riuniti, Bergamo, ItalyThe pathogenesis of high thrombotic risk in ET andPV patients is not completely clarified. In vivo PMNactivation (i.e. increased PMN surface CD11b expressionand protease release) occurs in these patientsand is associated with a hypercoagulable state. SinceCD11b plays an important role in PMN/platelet interaction,as a ligand for GPIb-bound fibrinogen onplatelet surface, in this study we explored whetherthe CD11b increment on PMN may be associatedwith changes in PMN/platelet interaction and inplatelet cell adhesion molecules. Forty-three patientswith ET, 30 with PV and 50 control subjects werestudied. PMN and platelet activation was evaluatedby surface CD11b and CD62P expression, respectively.PMN-platelet aggregates were defined as the percentageof CD11b-positive PMN co-expressing aplatelet-specific marker (i.e. CD42b or CD62P). Theseparameters were studied by whole blood flowcytometryin both basal condition and after in vitroPMN stimulation by f-MLP. Significantly higherCD11b levels on PMN from ET and PV patients vscontrols were found. PMN/platelets aggregates werealso increased (p