Interleukin 11 (IL-11), a member of the IL-6 family of cytokines, exerts pleiotropic activities by stimulating hemopoiesis and thrombopoiesis, regulating macrophage differentiation, and conferring mucosal protection in the intestine. These effects are mediated by a multimeric complex comprising the ligand-binding IL-11R± and the ubiquitously expressed gp130R-subunit, which together, trigger intracellular signaling and engagement of Stat3. Mature human IL-11 shares 88%, 88%, and 96% aa sequence identity with mouse, rat and canine IL-11, respectively. IL-11 is a pleotropic cytokine produced by lung stromal cells in response to respiratory viruses, cytokines, and histamine. The functions of IL-11 are that it directly stimulates the proliferation of hematopoietic stem cells and megakaryocyte progenitor cells, and induces megakaryocyte maturation resulting in increased platelet production.