Effects of interleukin 6 on megakaryocytes and on canine platelet function.

The multifunctional cytokine interleukin 6 (IL-6) is a potent promoter of megakaryocytic maturation in vitro. In vivo, IL-6 has similar effects on the maturation of megakaryocytes, as shown by enhancing size, ploidy and platelet production. IL-6 is capable of augmenting the platelet count in both normal animals and those with reduced megakaryocyte mass; ongoing clinical trials suggest a similar thrombocytopoietic effect in man. Moreover, IL-6 alters platelet function, rendering them more sensitive to activation by thrombin and platelet activating factor. Finally, IL-6 promotes increases in plasma fibrinogen and von Willebrand factor, and a decrease in free protein S concentration. These modifications of the platelet and coagulant phases of the clotting mechanism may result in an overall prohemostatic tendency, which may prove beneficial for the amelioration of bleeding propensity following chemotherapy. However, additional investigation will be required to determine if IL-6-mediated alterations of hemostasis may lead to pathologic thrombosis.