The pleiotropic cytokine, IL-11, has been shown to have proliferative and differentiation effects on lymphopoietic, myeloid and erythroid cells. IL-11 also has the inhibiting effect of repressing adipogenesis in vitro. The IL-11alpha receptor, IL-11Ralpha, is a member of the class 1 subgroup of the cytokine receptor family and exhibits structural similarity to the alpha subunits of the human ciliary neurotrophic factor (CNTF) and the mouse IL-6 receptor. It is speculated that the IL-11Ralpha regulates the proliferation and/or differentiation of skeletogenic progenitor and mesenchymal cells. Coexpression of gp130 and IL-11alpha is necessary for high-affinity binding of IL-11 to IL-11Ralpha. It has also been found that coexpression of IL-11Ralpha and gp130 is required for proper stimulation of Ba/F3 cells to differentiate into macrophage in response to IL-11.