Antidepressant drugs may help the immune system fight serious illness, research suggests. They enhance the activity of natural killer cells, key elements of the immune system, and could help the body combat infections such as HIV, and even cancer

Natural killer (NK) cells are white blood cells which home in on infected or cancerous cells, releasing agents that induce apoptosis, or "cell suicide". NK cells are especially active against viruses.

The research emerged from findings that stress and depression impair NK cell function and can accelerate the progress of HIV/ Aids. Scientists recruited depressed and non-depressed HIV-positive women and treated them with three drugs to treat stress and depression. Two, Citalopram and the "substance P antagonist" CP-96345 increased NK cell activity, while RU486 had no effect.

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The study leader, Dr Dwight Evans of the University of Pennsylvania in Philadelphia, said: "The findings show that natural killer cell function in HIV infection may be enhanced by selective serotonin re-uptake inhibition and substance P antagonism." The results are published inBiological Psychiatry.