Scientists have discovered that AIDS isn't the result of HIV's effects on the immune cells, but rather the way in which cells interact with each other once they have become infected. HIV takes its toll in one of two ways: one is that it becomes a free-floating virus that infects immune cells; the other is cell-to-cell transmission which is up to 1000 times more efficient than the former.

A new study, published in Cell Reports, states that only the second method ends in "newly infected cells committing suicide", according to a press release. "The fundamental 'killing units' of CD4 T cells in lymphoid tissues are other infected cells, not the free virus," says co-first author Gilad Doitsh, a staff research investigator at the Gladstone Institute of Virology and Immunology in California. "And cell-to-cell transmission of HIV is required for activation of the main HIV death pathway."

A previous investigation from the researchers at Gladstone Institute revealed that 95% of cell death of those infected with HIV came as a result of "self-defence" suicide. Nonetheless, fragments of viral DNA are picked up by other cells which creates a domino effect. The latest study revealed that this death pathway is only a result of cell-to-cell transmission, not through the virus free-floating.

Co-first author Nicole Galloway, PhD, a post-doctoral fellow at the Gladstone Institute of Virology and Immunology, said: "Although free-floating viruses establish the initial infection, it is the subsequent cell-to-cell spread of HIV that causes massive CD4 T cell death. Cell-to-cell transmission of HIV is absolutely required for activation of the pathogenic HIV cell-death pathway."

Senior author Warner C Greene, MD, PhD, director of the Gladstone Institute of Virology and Immunology, added: "This study fundamentally changes our mindset about how HIV causes massive cell death, and puts the spotlight squarely on the infected cells in lymphoid tissues rather than the free virus. By preventing cell-to-cell transmission, we may able to block the death pathway and stop the progression from HIV infection to AIDS."