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 t o CD4+ T cells in the absence of productive infection of the APC. Fluoresce nt latex beads were used to define the endocytic pathways that may contribu te to this non-infectious pathway of virus carriage. Beads between 14 nm an d 2300 nm in diameter were taken up by uncultured blood DC, but uptake of b eads larger than 280 nm was much reduced in the DC compared to monocytes. A fter culture, there was a reduction in bead carriage in DC compared to mono cytes. In the DC, beads were found as small aggregates in class II containi ng compartments or as single beads just below the cell surface. Beads accum ulated in monocytes as aggregates in class II negative compartments. Bead r ecycling occurred in DC, but not in the fresh or cultured monocytes. Electr on microscopy of HIV-l-pulsed DC cultured with CD4+ T cells showed accumula tion of apoptotic debris and virions within endosomes in the DC. The periph eral location and recycling of endocytosed material in DC provides a pathwa y for virion transfer from DC to T cells that does not occur in monocytes.