When human T-cells bump into each they form a sticky strand that connects the two cells. These strands dubbed "membrane nanotubes" by the Imperial College scientists who discovered them can connect two T-cells that are several cell lengths apart. By infecting a T-cell with HIV containing GFP labelled proteins the researchers were able to show that HIV proteins travel down the nanotubes from infected to non-infected cells. These nanotubes maybe part of the reason HIV is so effective at spreading rapidly within host bodies.
FIG 1: Time-lapse imaging of GFP tagged proteins moving along a membrane nanotube connecting infected with uninfected T cells. The boxed regions in are enlarged to show that the protein-GFP reaches the initially uninfected T cell.