Interleukin-11 is a pleiotropic cytokine that was originally detected in the conditioned medium ofan IL-1α-stimulated primate bone marrow stromal cell line (PU-34) as a mitogen for the IL-6-responsive mouse plasmacytoma cell line T11. IL-11 has multiple effects on both hematopoietic and non-hematopoietic cells. Many of the biological effects described for IL-11 overlap with 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 alsoenhances the IL-3-dependent megakaryocyte colony formation. IL-11 has been found to stimulate the T cell-dependent development of specific immunoglobulin-secreting B cells.