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Tuberculosis vaccines under development might be powerless in developing countries, researchers have warned.

They say this is because research is not taking into account the different immune systems of people in the South.

The standard BCG vaccine is used worldwide against tuberculosis. It works by stimulating the production of 'TH1' immune cells. New vaccines in development mimic this mechanism.

Yet, while boosting TH1 cells has been effective in industrialised countries, it is failing in developing countries — where the disease kills the most people.

Writing in Nature Review Immunology, the researchers say the BCG vaccine does not work in people in developing countries because their immune system has a separate response that counteracts with the protective 'TH1' response.

In poor countries, people often come into contact with bacteria related to Mycobacterium tuberculosis — the microbe that causes tuberculosis. This means that their immune system is already primed to produce TH1 cells against the bacterium.

However, they are also exposed to parasitic worms that provoke a response from a second type of immune cell, known as TH2.

As a result, their bodies continually produce a baseline level of TH2 cells. These cells are able to oppose the TH1 response.

The BCG vaccine boosts the TH1 response, but does not dampen the TH2 one. As a result, the vaccine does not prevent people in developing countries from getting the disease.

Designing a vaccine that targets this harmful mechanism would be more likely to work, say the researchers.

So far, however, their theory has only been tested in animals, and is awaiting tests in people.

Reference: Nature Reviews Immunology 5, 661 (2005)

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