DENDRITIC CELL-DEVELOPMENT IN CULTURE FROM THYMIC PRECURSOR CELLS IN THE ABSENCE OF GRANULOCYTE MACROPHAGE COLONY-STIMULATING FACTOR/

The earliest lymphoid precursor population in the adult mouse thymus h ad previously been shown to produce not only T cells, but also dendrit ic cell (DC) progeny on transfer to irradiated recipients. In this stu dy, culture of these isolated thymic precursors with a mixture of cyto kines induced them to proliferate and to differentiate to DC, but not to T lineage cells. At least 70% of the individual precursors had the capacity to form DC. The resultant DC were as effective as normal thym ic DC in the functional test of T cell stimulation in mixed leukocyte cultures. The cultured DC also expressed high levels of class I and cl ass II major histocompatibility complex, together with CD11c, DEC-205, CD80, and CD86, markers characteristic of mature DC in general. Howev er, they did not express CD8 alpha or BP-1, markers characteristic of normal thymic DC. The optimized mixture of five to seven cytokines req uired for DC development from these thymic precursors did not include, granulocyte/macrophage colony stimulating factor (GM-CSF), usually re quired for DC development in culture. The addition of anti-GM-CSF anti body or the use of precursors from GM-CSF-deficient mice did not preve nt DC development. Addition of GM-CSF was without effect on DC yield w hen interleukin (IL) 3 and IL-7 were present, although some stimulatio n by GM-CSF was noted in their absence. In contrast, DC development wa s enhanced by addition of the Flt3/Flk2 ligand, in line with the effec ts of the administration of this cytokine in vivo. The results indicat e that the development of a particular lineage of DC, probably those o f lymphoid precursor origin, may be independent of the myeloid hormone GM-CSF.