MicroMicrobe

Bacteria wear viral disguise to avoid immune system

Our immune system does an awesome job of protecting us every day from bacteria and viruses that enter our bodies. To overcome this brilliant barrier, bacteria have developed some clever strategies to avoid clearance from our immune system. This includes mimicking our own cells (molecular mimicry), killing or hiding in white blood cells and suppression of our immune response by secretion of toxins. Now a recent study has found bacteria can avoid the immune system by activating a response only effective against viruses.

Interferons are proteins secreted by our cells upon invasion of a pathogen, which activate our immune system to attack. They act differently depending on whether a virus or bacterium has breached our barriers; type I response is used against viruses and a type II response is used against bacteria. Researchers at the University of California studied interferon responses induced by Mycobacterium leprae, with some unexpected results. They found the bacterium acted as a wolf in sheep’s clothing, stimulating a type I response in patients with severe disease, which is ineffective against bacteria. Interestingly, those with milder disease had type II responses. When the type I response is activated, this inhibits the type II response, therefore working in M. leprae’s favour. This protection may explain why bacterial infections occur in patients with viral disease. 

This study has shown that bacteria not only mimic our own cells to avoid our immune system, but can also mimic a virus, inducing the wrong immune response. With further exploration on how bacteria stimulate a viral interferon response, therapeutics could be developed to shift interferon responses back to a type II response to stimulate milder symptoms in not only leprosy cases, but also tuberculosis and other diseases.