Serum levels of thrombopoietin, IL-11, and IL-6 in pediatric thrombocytopenias

We measured serum levels of thrombopoietin (TPO), interleukin (IL)-11, and IL-6 in 90 different samples from 67 pediatric patients with thrombocytopen ia (TP). The cytokine levels were determined by enzyme-linked immunosorbent assays (ELISA), and the biological activity of TPO was measured using a ce ll line transfected with human c-mpl. In patients with impaired megakaryocy topoiesis, as found in diseases such as aplastic anemia, amegakaryocytic TP , or TP with absent radii, we found TPO levels which were highly elevated c ompared with normal values (mean = 261 AU/ml, n = 52, vs. 22 AU/ml in healt hy controls). In contrast, patients suffering from idiopathic thrombocytope nic purpura (mean = 16 AU/ml, n = 31) or platelet function defects (mean = 23 AU/ml, n = 7) demonstrated normal TPO levels. The biological activity te sted in the bioassay correlated well with the ELISA data. However, sera of some patients with amegakaryocytic TP demonstrated a remarkably higher biol ogical activity of TPO than expected from the ELISA data. Within the differ ent groups there was no correlation between platelet counts and TPO levels. Only 27% of all samples had elevated levels of IL-11 (mean = 450 pg/ml, n = 20). Elevated IL-6 serum levels were detected in only 13% of all samples analyzed (mean = 42 pg/ml, n = 12). We conclude that megakaryocytopoiesis i s regulated mainly by TPO, that it is dependent on the platelet and the meg akaryocytic mass, and that IL-11 plays an additional role in supporting the platelet production. IL-6 does not appear to be up-regulated in children w ith thrombocytopenia.