The direct transfer of HIV between immune cells, rather than free-floating copies of the virus, is apparently largely responsible for immune cell death and the progression to AIDS. Publishing their findings in Cell Reports, researchers built on previous findings about how a fiery form of cell suicide is likely the mechanism that leads to overall immune decline. In their new research, they studied HIV-infected lymphoid tissue to compare the cell death rates based on whether cells were infected by direct transfer from an infected immune cell or a by free-floating virus.

They found that there was significantly more death among CD4 immune cells when they were infected through cell-to-cell transfer than by free-floating HIV.

"Although free-floating viruses establish the initial infection, it is the subsequent cell-to-cell spread of HIV that causes massive CD4 cell death,” the study’s co-first author Nicole Galloway, PhD, a post-doctoral fellow at the Gladstone Institute of Virology and Immunology in San Francisco, said in a press release. “Cell-to-cell transmission of HIV is absolutely required for activation of the pathogenic HIV cell-death pathway.”

The researchers also found that if they disrupted cell-to-cell contact, they effectively stopped CD4s from dying.

They speculate that the increased efficiency of HIV’s transmission between cells, compared with infections from free-floating virus, accounts for the difference in cell death rates.

To read a press release about the study, click here.

To read the study abstract, click here.