COMPARISON OF THE FUNCTIONAL PROPERTIES OF MURINE DENDRITIC CELLS GENERATED IN VIVO WITH FLT3 LIGAND, GM-CSF AND FLT3 LIGAND PLUS GM-CSF

Flt3 ligand (FL) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are important growth factors for dendritic cells (DC). Substantial numbers of DC can be generated in vivo following the administration of either factor. We sought to extend our knowledge of the functional properties of these cells including their ability to prime naı̈ve CD8+ T cells. In addition, we compared the nature of the DC generated in vivo with the single cytokines to those generated with the combination of FL+polyethylene glycol-modified GM-CSF (pGM-CSF). Treatment with FL+pGM-CSF yielded greater numbers of both CD11blow and CD11bhigh DC than with either cytokine alone, and these DC were more efficient at antigen (Ag) capture. The FL+pGM-CSF-generated CD11blow DC lacked expression of CD8α. Following treatment with LPS in vivo, all DC subsets upregulated CD40, CD80, CD86, and MHC class II expression, but surprisingly Ag capture was not downregulated and some DC subsets retained expression of intracellular MHC class II vesicles. Thus, even after activation in vivo with LPS, DC retained Ag capture properties of immature DC, and Ag presentation/costimulation properties of mature DC. Though all DC subsets stimulated CD4+ T cell proliferation equivalently, FL-generated DC were more efficient at priming Ag-specific CD8+ cytolytic T cells than DC generated with either pGM-CSF alone or FL+pGM-CSF, and CD11bhigh DC were more efficient at priming CD8+ T cells than CD11blow DC.