CLONED DENDRITIC CELLS CAN PRESENT EXOGENOUS ANTIGENS ON BOTH MHC CLASS-I AND CLASS-II MOLECULES

Pathways for presenting proteins from the extracellular fluids on MHC class I molecules have been described in macrophages. However, it is u ncertain whether similar mechanisms exist in dendritic cells, because conventional preparations of these cells can be contaminated with macr ophages. We addressed this issue by transducing granulocyte-macrophage CSF into bone marrow cultures followed by supertransfection with myc and raf oncogenes. These immortalized clones displayed dendritic morph ology, and many expressed the dendritic cell-specific markers DEC-205 and 33D1 as well as high levels of MHC molecules and costimulatory mol ecules. Using these cloned dendritic cells, we found that exogenous OV A could be presented on both their MHC class I and class II molecules. This presentation was markedly enhanced when the Ag was particulate a nd internalized by phagocytosis. Presentation of particulate OVA on MH C class I molecules was insensitive to the weak base chloroquine, but was blocked by peptide aldehyde inhibitors of the proteasome, indicati ng that the class I-presented peptides were generated in the cytosol. Brefeldin A, which inhibits the exocytosis of newly synthesized protei ns from the endoplasmic reticulum, also inhibited Ag presentation. The se results establish that dendritic cells can present exogenous Ags on MHC class I molecules and appear to use a similar phagosome to cytoso l pathway as macrophages. Therefore, dendritic cells are likely to pla y an important role in generating immune responses to tissue transplan ts and tumors in vivo. Furthermore, these findings provide an approach for targeting vaccine Ags into these cells to prime immune responses in vivo.