PlagueHow plague attacks us – and how we should defend ourselves

Published 22 June 2017

The plague that is believed to have caused the Black Death still occasionally ravages populations, albeit to a much smaller extent than before. Now we know more about how the bacteria attack us. But how does the plague bacterium attack human beings, and how does the body defend against its constantly evolving attacks? New research on the bacterium is yielding new answers.

The plague that is believed to have caused the Black Death still occasionally ravages populations, albeit to a much smaller extent than before. Now we know more about how the bacteria attack us.

But how does the plague bacterium attack human beings, and how does the body defend against its constantly evolving attacks? New research on the bacterium is yielding new answers.

An “arms race”
Evolution seems to work like an “arms race” between bacteria and humans.

Bacteria attack the human body in new ways, but over several generations, human beings become better at fighting them and build resistance to the attacks – at least until the bacteria find new and different means of attacking us.

To put it another way, bacteria find ways to inhibit immune responses, but the body also develops new ways to circumvent the blockade and to recognize the infection. “We can only hope that humans win in the end!” says Egil Lien, an adjunct professor in NTNU’s Department of Cancer Research and Molecular Medicine.

Lien is part of a group at the NTNU-CEMIR research center, which among other things investigates how bacteria attack people. For this project, Lien’s group researched bacterial effector proteins.

Confuses human cells
Effector proteins are signal substances from bacteria that trigger a particular reaction when they enter a host cell. Many bacteria that cause disease typically use specialized secretion systems to introduce their effector proteins into human cells.

These effector proteins can have various functions, but their main purpose is to provide a good growing environment for the invading bacteria.

Bacteria can stop attacks and bacteria-inhibiting activities on themselves by blocking the host cells’ immune responses, which is often the task of the innate immune system.

Put simply, bacteria can use the effector proteins to create chaos inside cells, allowing the infection to spread without being effectively stopped.

Multiple methods
Bacteria can secrete effector proteins in several ways. One of the best-known methods is the type 3 secretion system, which is found in various disease-causing pathogens such as salmonella, E. coli, shigella and Yersinia.

“These secretion systems are sophisticated nanomachines,” says Lien. “They form a ‘needle’ from the bacterium and create a pore in the target cell membrane that the effector proteins are released into.”

Researchers associated with NTNU-CEMIR use Yersinia pestis – that is, the bacterium that causes bubonic plague – as a model system that demonstrates how several types of bacteria work.