CD40-ligand stimulates myelopoiesis by regulating flt3-ligand and thrombopoietin production in bone marrow stromal cells

CD40 ligand (CD40L)/CD40 interactions play a central role in T-cell-depende nt B-cell activation as previously shown by in vitro studies, the phenotype of CD40L knockout mice and the defective expression of CD40L in patients w ho have X-linked immunodeficiency with hyper-IgM, The distribution of CD40 in cells other than of myeloid and lymphoid lineages has suggested addition al functions for this receptor/ligand couple. Here we show that CD40L stimu lates myelopoiesis with a noticeable effect on megakaryocytopoiesis in cocu ltures of hematopoietic progenitor cells and bone marrow stromal cells. The se results suggest a mechanism by which T-cell or platelet-associated or so luble CD40L may regulate myelopoiesis. (C) 2000 by The American Society of Hematology.