CD40 ligand (CD40L)/CD40 interactions play a central role in T-cell–dependent B-cell activation as previously shown by in vitro studies, the phenotype of CD40L knockout mice and the defective expression of CD40L in patients who have X-linked immunodeficiency with hyper-IgM. The distribution of CD40 in cells other than of myeloid and lymphoid lineages has suggested additional functions for this receptor/ligand couple. Here we show that CD40L stimulates myelopoiesis with a noticeable effect on megakaryocytopoiesis in cocultures of hematopoietic progenitor cells and bone marrow stromal cells. These results suggest a mechanism by which T-cell or platelet-associated or soluble CD40L may regulate myelopoiesis.

No abstract

presence of VASA-positive and DAZL-positive cells, strongly indicates that the cells reached the spermatogonia/spermatocyte cell stage. Cells that were positive for VASA and DAZL without OCT4 expression also suggest that a fraction of cells were able to progress to the advanced meiotic stages of in vitro spermatogenesis.CONCLUSIONS: Our attempt to use the HD method together with the two-step culture system to induce the appearance and eventual maturation of male germ cells has shed light on the mechanisms of spermatogenesis in vitro. Using pluripotent stem cells to generate germ cells may benefit men afflicted by spermatogenic failure.