Low serum levels of interleukin-6 in children with post-infective acute thrombocytopenic purpura.

Interleukin-6 plays an important role in host defense mechanisms and it appears to be a major mediator of the acute-phase response. IL-6 is also an important thrombocytopoietic factor. High serum levels of IL-6 are present in reactive thrombocytosis. The number and function of circulating platelets are the major factors that affect megakaryocytopoiesis by thrombopoietin. High levels of thrombopoietin have been observed in patients with thrombocytopenic purpura. To evaluate a possible thrombopoietin-like function of IL-6, we measured IL-6 levels in the serum of patients affected by post-infective acute thrombocytopenic purpura using a sensitive ELISSA assay. As controls, we studied normal subjects and patients with reactive thrombocytosis. No significant difference was observed between thrombocytopenic patients and normal controls. High IL-6 levels were present in patients with reactive thrombocytosis. In conclusion, we had not observed high levels of IL-6 in acute thrombocytopenic purpura and, very probably, IL-6 is not involved in the regulation of platelet mass for the hemostatic function. The thrombocytopoietic activity of IL-6 is another acute-phase response and it is consistent with the other functions of this cytokine. This suggests an active participation of platelets in host defense mechanisms.