IL-11 is secreted by bone marrow stromal cells (fibroblasts) and is produced also by a number of mesenchymal cells. The IL-11 receptor (alpha chain) utilizes gp130 as its signal transducer, which is also a component of other cytokine receptors. The alpha chain of the IL-11 receptor has been identified independently as Etl2. IL-11 promotes primary and secondary immune responses in vitro and in vivo and modulates antigen-specific antibody reactions. IL-11 promotes the proliferation of IL-6 dependent plasmacytoma cell lines in the presence of neutralizing IL6 antibodies. IL-11 also stimulates the T cell dependent development of IgG-secreting B cells in spleen cell cultures. IL-11 inhibits the differentiation of pre-adipocytes. It induces the synthesis of some acute phase proteins by hepatocytes.