Cytokines, endothelium, and adhesive molecules in pathologic thrombopoiesis

Clonal thrombocytosis (CT) associated with myeloproliferative disorders (MPD) is believed to be secondary to autonomous unregulated platelet production. Secondary or reactive thrombocytosis (RT) can be observed in a number of clinical circumstances and may be related to persistent production of some thrombopoietic factors acting on megakaryocytes (MK). The goal of this study is to assess the serum concentrations of these cytokines in control subjects and patients with MPD associated with thrombocythemia, RT, and autoimmune thrombocytopenic purpura (ATP). Eleven patients with MPD, five with chronic myeloid leukemia (CML), three with polycythemia vera (PCV), two with essential thrombocythemia (ET), one with myelofibrosis, 15 with RT, eight with ATP, and 12 healthy volunteers were enrolled in the study. Serum interleukin (IL)-1β, IL-6, tumor necrosis factor-alpha (TNF), fibronectin, intracellular adhesion molecule-1 (ICAM-1), and thrombomodulin (TM) were measured in these groups. Interleukin-1β, IL-6, and TNF levels were high in patients with RT and ATP, suggesting that these cytokines act on early uncommitted progenitors, promoting commitment along the MK lineage and leading to thrombocytosis or compensation for thrombocytopenia. TM was significantly increased in patients with MPD compared to all other groups, probably indicating the presence of subclinical endothelial damage. Fibronectin levels were high in MPD and RT patients. This finding can be secondary to high platelet turnover in these patients. We found that ICAM-1 levels were high in patients with clonal thrombocytosis. ICAM-1 can be one of the factors initiating the events ultimately leading to clonal thrombocytosis. Thrombocythemia associated with MPD is an autonomous phenomenon not regulated by cytokines.