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), analyzed 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 1.4 million deaths in 2011.
By analyzing 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 of the Blizard Institute, part of Queen Mary, who led the research, says, "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."
By analyzing blood samples taken from 85 of the original cohort after an eight-week period of intensive treatment, the researchers found that ethnic variation in immune responses became even more marked. A number of immunological biomarkers, which correlated with either fast or slow clearance of the TB bacteria, were identified and found to differ between Africans and Europeans/Asians.
Dr. Anna Coussens, who measured immune responses in patient samples at NIMR, says, "These findings have important implications, both for the development of new diagnostic tests, which increasingly rely on analysing the immune response, and also for work to identify candidate biomarkers to measure response to anti-TB treatment. In the future, diagnostic tests and biomarkers will need to be validated in different ethnic populations."
A key factor in determining the ethnic variation identified in the study appears to be the patients' genetic type of vitamin D binding protein a molecule which binds vitamin D in the circulation.
Martineau notes, "There are different genetic types of this protein which vary in frequency between ethnic groups, adding to the growing evidence that vitamin D and the way it is carried in the blood is crucial in determining how a patient's immune system will respond to TB."
Further studies in other populations are now needed to validate the ethnic difference identified.
This work was funded by the British Lung Foundation and the Medical Research Council (MRC).