Fig. 1

Mechanisms of HIV-1 cell-to-cell transmission. a Infected and uninfected T cells come in contact to form a virological synapse. HIV-1 gains access to the cytoplasm of the target cell by direct fusion at the plasma membrane or eventually after endocytosis. This structure is dependent on Env/CD4 interaction, adhesion molecules (LFA-1/ICAM-1) interaction, and the cytoskeleton. b Uninfected macrophages or dendritic cells (DC) store HIV-1 particles in intracellular compartments after capture via DC-SIGN or SIGLEC-1. These particles can be released and transferred to CD4⁺ T cells through the infectious synapse. c HIV-1 surfs along nanotubes between uninfected and infected T cells. d Macrophages can be infected after phagocytosis of infected CD4⁺ T cells. e Macrophages can fuse with infected CD4⁺ T cells and with surrounding uninfected macrophages to form multinucleated giant cells. Donor cells are in brown and uninfected cells in blue