Scientists discover ethnic differences in immune response to TB bacterium

The immune response to the bacterium that causes tuberculosis (TB) varies between patients of different ethnic origin, raising important implications for the development of tests to diagnose and monitor treatment for the disease, according to new research published today in the journal PLOS Pathogens.

The study, led by researchers at Queen Mary, University of London, in collaboration with the Medical Research Council's National Institute for Medical Research (NIMR),analysed the immune response of 128 newly-diagnosed TB patients in London who were divided by ethnicity into those of African (45), European (27), Asian (55) or mixed European/Asian (1) ancestry.

TB is an infection caused by the TB bacterium Mycobacterium tuberculosis. It commonly affects the lungs. While it grew rare in the UK due to BCG vaccination, improvements in living standards and the introduction of effective antibiotic treatment, it has been on the increase since the late 1980s. TB also remains a major global health problem, responsible for nearly nine million new cases and 1.4million deaths in 2011.

By analysing the levels of various inflammatory markers in blood samples taken before treatment, the scientists showed that immune responses of Asians and Europeans were similar to each other, but different from those of Africans. This difference was caused by ethnic variation in the patients' genetic make-up and was not related to the strain of TB bacterium that the patients were infected with.

Dr Adrian Martineau, Reader in Respiratory Infection and Immunity at the Blizard Institute, part of Queen Mary, who led the research, said: "The TB bacterium has co-evolved with humans following migration to Europe and Asia some 70,000 years ago, and different strains of the TB bacterium disproportionately infect particular ethnic groups. Experiments with white blood cells cultured in the lab have shown that different strains of the TB bacterium elicit different amounts of inflammation. One might therefore expect that TB patients' immune responses would differ according to the strain of TB bacterium that they are infected with.

"However our study has shown, for the first time, that it is actually ethnic differences in the patient's genetic make-up that cause most of this variation in immune responses – with little effect of the TB strain they are infected with."

Tuberculosis facts

Tuberculosis (TB) is an infection, primarily in the lungs (a pneumonia), caused by bacteria called Mycobacterium tuberculosis. It is spread usually from person to person by breathing infected air during close contact.
TB can remain in an inactive (dormant) state for years without causing symptoms or spreading to other people.
When the immune system of a patient with dormant TB is weakened, the TB can become active (reactivate) and cause infection in the lungs or other parts of the body.