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Scientists Explain Declining Immune Response in AIDS Patients

Scientists Explain Declining Immune Response in AIDS Patients

Victor Appay of the Institute of Molecular Medicine at the John Radcliffe Hospital in Oxford, UK, and his colleagues explain in the Journal of Experimental Medicine that certain anti-viral “killer T cells” in people infected with HIV lose their sting over time.

CD8 T lymphocytes, commonly called “killer T cells,” are part of the body’s front-line of defense. They kill virus-infected cells and produce anti-viral proteins that interfere with virus multiplication. In CD8 T cells that recognize HIV antigens and attack HIV-infected cells, HIV hinders the former function.

In patients who have the virus but have yet to develop AIDS, CD8 T lymphocytes produce small amounts of perforin, a protein that leads to the death of an infected cell. The CD8 T lymphocytes continue to release normal amounts of cytokine proteins, which help kill the virus directly.

To fully mature, CD8 T cells need the help of CD4 T cells. However, HIV directly infects and switches off CD4 cells. Their gradual loss brings on the severely immunodeficient state of AIDS. It is theorized that the disappearance of CD4 T cells also strands the HIV-responsive CD8 T cells at an immature stage of development. The stunted CD8 T cells continue to produce anti-viral proteins, however.

For years, scientists have wondered why the immune systems of HIV-infected patients hold the virus in check for years without eradicating it completely. These findings may help explain what happens during this silent period of chronic HIV infection.

-- Paiyarut Kanjanavaikoon