Uptake of HIV and latex particles by fresh and cultured dendritic cells and monocytes

Blood dendritic cells (DC) efficiently carry HIV-1 and transmit infection to CD4+ T cells in the absence of productive infection of the APC. Fluorescent latex beads were used to define the endocytic pathways that may contribute to this non-infectious pathway of virus carriage. Beads between 14 nm and 2300 nm in diameter were taken up by uncultured blood DC, but uptake of beads larger than 280 nm was much reduced in the DC compared to monocytes. After culture, there was a reduction in bead carriage in DC compared to monocytes. In the DC, beads were found as small aggregates in class II containing compartments or as single beads just below the cell surface. Beads accumulated in monocytes as aggregates in class II negative compartments. Bead recycling occurred in DC, but not in the fresh or cultured monocytes. Electron microscopy of HIV-1-pulsed DC cultured with CD4+ T cells showed accumulation of apoptotic debris and virions within endosomes in the DC. The peripheral location and recycling of endocytosed material in DC provides a pathway for virion transfer from DC to T cells that does not occur in monocytes.