NEOPLASIA Brief report Molecular mimicry in the chronic myeloproliferative disorders: reciprocity between quantitative JAK2

V617F) is present in the chronic myelopro-liferative disorders (MPDs), polycythemia vera (PV), idiopathic myelofibrosis (IMF), and essential thrombocytosis (ET). JAK2 is also a chaperone for Mpl and respon-sible for its cell-surface expression. We observed a reciprocal relationship be-tween neutrophil JAK2 V617F allele per-centage and platelet Mpl expression in JAK2 V617F–positive PV, IMF, and ET patients. However, severely impaired platelet Mpl expression was present in JAK2 V617F–negative MPD patients. While JAK2 V617F allele status did not necessarily correlate with the clinical MPD phenotype, the degree of impaired plate-let Mpl expression did. We conclude that multiple molecular abnormalities are in-volved in the pathogenesis of the MPDs and that aberrant Mpl expression may be a common denominator of aberrant sig-naling in both the JAK2 V617F–positiv