Interleukin-11 (IL-11) is a pleiotropic cytokine that was originally detected in the conditioned medium of an IL-1a-stimulated primate bone marrow stromal cell line (PU-34) as a mitogen for the IL-6-responsive mouse plasmacytoma cell line T11. IL-11 contains no cysteine residues or potential glycosylation sites. IL-11 has multiple effects on both hematopoietic and nonhematopoietic cells. Many of the biological effects described for IL-11 overlap those for IL-6. In vitro, IL-11 can synergize with IL-3, IL-4 and SCF to shorten the G0 period of early hematopoietic progenitors. IL-11 also enhances the IL-3-dependent megakaryocyte colony formation. IL-11 has been found to stimulate the T cell dependent development of specific immunoglobulin-secreting B cell.