Epidermal and mucosal dendritic cells and HIV1 infection.

The major modes of HIV1 transmission involve circumstances and behavior that promote exchange of blood or body fluids containing HIV virus and/or HIV infected cells. In the second group, semen, vaginal secretions, exudates and occasionally saliva have been documented as sources of transmission. If the skin, protected by the horny layer, does not seem easily infected, the mucous membrane and especially the vaginal, rectal or oral mucosa are the main sites of HIV entry in absence of lesions. In mucosa, a well identified population of dendritic cells may be considered as the first target of HIV1: the Langerhans cells. Originated from the bone marrow, the Langerhans cells migrate into the peripheral epithelia (skin, mucous membranes) and play a key role in the immune surveillance system against foreign antigens. They act as antigenpresenting cells through a specific cooperation with CD4+ lymphocytes after migration to the proximal lymph nodes. As HIV1-susceptible cells, Langerhans cells in genital or rectal mucosa may be the first infected cell type and may be the vectors of infection for CD4 positive T cells. It is clearly demonstrated that LC may be infected in HIV1 seropositive patients. Recently in vitro, experimental infection of Langerhans cells was reproduced using a co-culture assay with HIV1 infected cells. Recent data obtained with transgenic mice containing HIV1 gene underline the key role of Langerhans cells in the pathogenesis process of HIV infection.