Tissue dendritic cells as portals for HIV entry

Dendritic cells (DCs) are found at the portals of pathogen entry such as the mucosal surfaces of the respiratory, gastrointestinal and genital tracts where they represent the first line of contact between the immune system and the foreign invaders. They are found throughout the body in multiple subsets where they express unique combinations of C-type lectin receptors to best aid them in detection of pathogens associated with their anatomical location. DCs are important in the establishment in HIV infection for two reasons. Firstly, they are one of the first cells to encounter the virus, and the specific interaction that occurs between these cells and HIV is critical to HIV establishing a foothold infection. Secondly and most importantly, HIV is able to efficiently transfer the virus to its primary target cell, the CD4(+) T lymphocyte, in which it replicates explosively. Infection of CD4(+) T lymphocytes via DCs is far more efficient than direct infection. This review surveys the various DCs subsets found within the human sexual mucosa and their interactions with HIV. Mechanisms of HIV uptake are discussed as well as how the virus then traffics through the DC and is transferred to T cells. Until recently, most research has focussed on vaginal transmission despite the increased transmission rate associated with anal intercourse. Here, we also discuss recent advances in our understanding of HIV transmission in the colon.