How TB Tricks the Body

The bacterium uses the body’s immune defences to obtain shelter and then multiply

Tuberculosis remains one of the world’s leading health threats, despite a century of effort directed at combating the disease. Estimates suggest that a third of the world’s population is infected by TB, and even today over two million people die of the disease every year. One of the reasons the bacteria causing TB—Mycobacterium tuberculosis (Mtb)—is such a threat is that it seems to be able to render the body’s immune defences useless. Now a recent paper published in Proceedings of the National Academy of Sciences provides an answer to how Mtb is able to manage this feat.

Under normal circumstances, specialised human immune cells called macrophages identify and destroy invading micro-organisms. They usually surround these invading organisms, seclude them, and then release adid enzymes in the secluded area to destroy them.Researchers at University of British Columbia have found that Mtb manages to use this very process to replicate. According to a university press release ‘once the bacteria become engulfed by macrophages, they secrete a protein named PtpA that disables the two separate mechanisms required for making the acidic environment that normally targets them. The end result is that Mtb lives comfortably in the immune cells, like a Trojan horse, hidden from the rest of the immune system. The bacteria then multiply inside the macrophage, and when released, they attack the body.’

“TB has been able to completely mislead our immune systems, convincing our body it isn’t there, which is why it is such an effective killer,” says Dr Yossef Av-Gay, lead researcher. “We discovered that the cells in charge of targeting and destroying invading bacteria are being fooled by a special protein that blocks the immune cells ability to recognise and destroy it. We have been engaged in studying the interaction between the TB bacterium and the human macrophage over the past decade,” says Av-Gay. “We are delighted with this discovery. Through learning about the tricks it uses, we now have new targets, so that we can develop better drugs against this devastating disease.”

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Hartosh Singh Bal