Dendritic cells and the replication of HIV-1

Dendritic cells (DCs) are a distinct lineage of white cells that arise from CD34+ progenitors in the bone marrow. DCs exhibit many specializations that lead to efficient antigen capture and presentation to T cells, both CD4+ helpers and CD8+ killers. In several human tissues, DCs express the CD4 receptor for HIV-1. Some early reports described the explosive infection of blood-derived DCs by HIV-1 and a severe compromise of their presenting function. In contrast, other studies described active HIV-1 replication when DCs were interacting with CD4+ T cells. This productive infection could begin with a low viral burden in DCs but required that the DCs retain their normal binding and stimulatory function for T cells. In this review we first summarize those features of the DC system that seem pertinent to HIV-1 infection. Then we consider the current literature on the interaction of HIV-1 with DCs, from several different tissues, in HIV-1-infected patients or following challenge with HIV-1 in vitro. The literature leads to the hypothesis that HIV-1 infection is a battleground in which DCs could be leading both of the armies, the aggressor that promotes HIV-1 replication from relatively small numbers of infected cells and the defender that mediates T cell-dependent resistance.