Researchers from Massachusetts General Hospital (MGH) claimed that HIV which infects and destroys CD4-positive helper T cells also uses those cells to travel through the body and infect other CD4 T cells.
CD4 T cells direct and support the infection-fighting activities of other immune cells.
"We have found that HIV disseminates in the body of an infected individual by 'hitching a ride' on the T cells it infects," Thorsten Mempel from MGH Center for Immunology and Inflammatory Diseases who led the study, said.
"Infected T cells continue doing what they usually do, migrating within and between tissues such as lymph nodes, and in doing so they carry HIV to remote locations that free virus could not reach as easily," Mempel said in a statement.
When HIV is introduced into blood or tissues, the virus binds to CD4 molecules on the surface of helper T cells, injecting its contents into cells and setting off a process that leads to the assembly and release of new virus particles.
It has long been assumed that these free virus travel by diffusion through tissue fluids to encounter new cells that can be infected.
Recent studies have suggested that HIV can also pass directly from cell to cell when structures called virological synapses form during long-lasting interactions between T cells.
Since CD4 T cells usually migrate quickly and form only transient contacts with other cells, the current study was designed to examine whether HIV alters the migration of infected T cells, allowing the kind of persistent contact that facilitates the spread of infection.
The team used a humanised mouse model, which has what is essentially a human immune system and is the only non-primate that can be infected with HIV.
To test the role of T cell migration in HIV infection, the researchers injected a group of humanised mice with HIV and at the same time treated them with an agent that prevents T cells from leaving lymph nodes.
Two months later, levels of HIV in the bloodstream and in lymph nodes distant from the site of injection were much lower in the treated group than in untreated HIV-infected animals, supporting the importance of T cell migration to carry virus throughout the body.
