Monocyte Activation Studies in Patients with Essential Thrombocythemia.

Essential thrombocythemia (ET), polycythemia vera and mielofibrosis with mieloid metaplasia (MMM) are myeloproliferative diseases that differ in their potential for developing bone marrow fibrosis. In addition to the role of megakaryocytes, the participation of monocytes in collagen deposits and fibroblast proliferation in the pathophysiology of MMM has already been described. We studied here monocyte activation in ET patients by measuring IL-2 receptor expression (CD25) in ex vivo monocytes and after its adhesion to polyestirene. Besides, we evaluated IL-1-b released by mononuclear cells after 24 hs culture. We evaluated 14 untreated ET patients. Blood samples were obtained under sterility conditions and mononuclear cells were separated by Ficoll-Hypaque gradient. CD25 positivity was evaluated by flow cytometry identifying monocytes as the CD14 + population before and after 18 hs cell culture in IMDM and 2% albumin. IL-1b was measured by ELISA technique in the supernatant of cells cultured in IMDM supplemented with 10% FCS during 18 hs. There were no statistical differences in CD25 expression in ET patients (n=8) neither before (3.1%, 1–11.4%) (median and range) nor after (15.2%, 4.7–39.3%) cell culture of CD14 population compared to normal controls (n=12, 2.0%, 0.2–10.3% and 20.3%, 1.4–34.3%, respectively). Levels of IL-1b were found decreased in patients with ET (n=10), 481 pg/ml, 53–1290 pg/ml, compared to normal controls (n=11), 779 pg/ml, 68.7–2166 pg/ml, although not reaching statistical difference (p=0.057). In conclusion, we did not find monocyte activation in ET patients as demonstrated by CD25 expression and IL-1b release. These results suggest that there is not a constitutive or induced activation of monocytes in ET but a trend towards a decreased capacity of activation. We believe this different monocyte behaviour from ET patients compared to that described in MMM patients could account for the dissimilar natural course of these diseases.