New York, Aug 28 (IANS): Instead of directly causing AIDS, the human immunodeficiency virus (HIV) turns host immune cells into suicide machines, using them to spread the virus and cause the progression from HIV to AIDS, new research has revealed.

HIV can either be spread through free-floating virus that directly infect the host immune cells or an infected cell can pass the virus to an uninfected cell.

The second method, cell to cell transmission, is 100 to 1000 times more efficient, and the new study shows that it is only this method that sets off a cellular chain reaction that ends in the newly infected cells committing suicide.

"The fundamental 'killing units' of CD4 T cells in lymphoid tissues are other infected cells, not the free virus," said co-first author Gilad Doitsh from Gladstone Institute of Virology and Immunology, University of California, San Francisco in the US.

HIV mostly targets CD4 T lymphocytes, a type of T cell involved in initiating an immune response.

"And cell-to-cell transmission of HIV is required for activation of the main HIV death pathway," Doitsh noted.

"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," senior author Warner Greene, director of the Gladstone Institute of Virology and Immunology pointed out.

"By preventing cell-to-cell transmission, we may able to block the death pathway and stop the progression from HIV infection to AIDS," Greene noted.

The study was published in the journal Cell Reports.