How has tuberculosis reshaped our immune systems?

Overview

COVID-19 is just the latest infectious disease to have had an enormous impact on human life. A recent study using ancient human DNA reveals how TB has affected European populations since the last 2,000 years, particularly the impact that this disease has had on the human immune system and genome. 

What is tuberculosis?

Tuberculosis is a potentially dangerous infectious bacterial disease that largely affects the lungs but can also attack your brain and spine. The bacteria that cause tuberculosis are transmitted when an infected person coughs, sneezes, talks, laughs and sings. Most people affected by the bacteria that cause tuberculosis do not actually exhibit symptoms. When symptoms do occur, they generally include a cough (sometimes blood-tinged), fever, night sweats and weight loss. Treatment of TB is not always required for people without symptoms, but patients with active symptoms will need a long course of treatment involving various antibiotics.

The research

A recent study using ancient human DNA reveals how TB has affected European populations since the last 2,000 years, particularly the impact that this disease has had on the genome. This work has indications for studying not only evolutionary genetics but even genetics that can influence your immune system.

This research centred on a variant of the gene TYK2 known as P1104A, which first author Gaspard Kerner had beforehand found to be linked with an enhanced risk of getting ill after infection with Mycobacterium tuberculosis when this variant is homozygous.

Further analysis showed that the incidence of the variant drastically sank about 2,000 years ago, around the point that present-day forms of infectious Mycobacterium tuberculosis variants became prevailing. The variant is not linked with other infectious viruses or bacteria.

In case you carry two copies of this gene variant in your genome, and you get infected with Mycobacterium tuberculosis, you are very prone to become sick and have a weak immune system. During the Bronze Age, this gene variant was much more prevalent, but we observed that it began to be negatively selected at a time that correlated with the beginning of the tuberculosis epidemic in Europe.

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