Screening for TB should take ethnicity into account (Image: Rex Features)

Your ethnic background could influence the way in which your body fights tuberculosis. Over the thousands of years that humans have been infected with TB, people of different ethnicities have evolved different immune mechanisms for handling the bacteria, a finding that could affect the outcome of planned trials for new TB drugs.

The body’s earliest immune reaction to bacterial infections such as TB is a set of intruder-fighting processes collectively called inflammation. This can include changes in levels of interferons – immune-signalling chemicals – as well as mobilisation of antibacterial white blood cells and platelets.

Adrian Martineau and colleagues at Queen Mary University of London measured 57 of these inflammation “markers” in 128 Londoners who were newly infected with TB, comparing them with the levels seen in healthy people. For the purposes of the study, the participants were grouped into two ethnic categories, namely African and Eurasian.


The team found that only four markers moved in the same direction, relative to the “typical” level, in both groups. The direction all the other markers moved in could be split according to which ethnic group the participants fell into. For example, in people of African descent who were slow to respond to anti-TB drugs, levels of anti-bacterial blood cells called neutrophils were unchanged, while a signalling chemical called interleukin-4 rose. In similar group of Eurasian people, neutrophils and interleukin-6 rose.

Protein variant

Normally such variations in immune response result from differences in the strain of the bacterium causing the infection, says Martineau. But the contrasting changes in markers in the two groups did not relate to the strain of TB involved. They did, however, correlate closely with an individual’s genetic variant of a protein that carries vitamin D in the blood, and that is also involved in several immune reactions. This protein varies between ethnic groups. What’s more, the differences in immune reactions between Africans and Eurasians in Martineau’s study became even more pronounced when they started taking medication for their TB.

“This starts to show us the mechanism for why TB differs between ethnic groups,” says Ajit Lalvani, head of TB at the National Heart and Lung Institute in London, who last year found that differences in the way TB affects the body are also linked to ethnicity. For example, he found that most infections in Europeans are in the lungs, for example, while Asians and Africans get most TB infections in other organs.

Tests to diagnose TB and to monitor the effects of treatment – including upcoming trials of new TB drugs – are based on tracking people’s immune reactions, as the bacteria themselves can be hard to detect.

That means the tests to measure the effectiveness of new TB drugs will have to be designed to take ethnic background into account. “We will have to be sure any given test works in our target population,” agrees Lalvani, who invented the first such test for TB a decade ago.

One option, says Martineau, may be to focus on the four immune markers that changed in the same direction in both groups.

Journal reference: PLoS Pathogens, DOI: 10.1371/journal.ppat.1003468

Additional reporting by Debora MacKenzie