Expression of multilectin receptors and comparative FITC-dextran uptake byhuman dendritic cells

Dendritic cells (DC) are potent antigen-presenting cells and understanding their mechanisms of antigen uptake is important for loading DC with antigen for immunotherapy. The multilectin receptors, DEC-205 and macrophage manno se receptor (MMR), are potential antigen-uptake receptors; therefore, we ex amined their expression and FITC-dextran uptake by various human DC prepara tions. The RT-PCR analysis detected low levels of DEC-205 mRNA in immature blood DC, Langerhans cells (LC) and immature monocyte-derived DC (Mo-DC), I ts mRNA expression increased markedly upon activation, indicating that DEC- 205 is an activation-associated molecule. In Mo-DC, the expression of cell- surface DEC-205 increased markedly during maturation. In blood DC, however, the cell-surface expression of DEC-205 did not change during activation, s uggesting the presence of a large intracellular pool of DEC-205 or post-tra nscriptional regulation. Immature Mo-DC expressed abundant MMR, but its exp ression diminished upon maturation. Blood DC and LC did not express detecta ble levels of the MMR, FITC-dextran uptake by both immature and activated b lood DC was 30- to 70-fold less than that of LC, immature Mo-DC and macroph ages. In contrast to immature Mo-DC, the FITC-dextran uptake by LC was not inhibited effectively by mannose, an inhibitor for MMR-mediated FITC-dextra n uptake. Thus, unlike Mo-DC, blood DC and LC do not use the MMR for carboh ydrate-conjugated antigen uptake and alternative receptors may yet be defin ed on these DC. Therefore, DEC-205 may have a different specificity as an a ntigen uptake receptor or contribute to an alternative DC function.